Category: Study Materials
-
Wavenumber: Definition, Properties, and Examples
Continue ReadingWavenumber
Wavenumber, also called wave number, a unit of frequency, often used in atomic, molecular, and nuclear spectroscopy, equal to the true frequency divided by the speed of the wave and thus equal to the number of waves in a unit distance.
Physicists and pharmacists often use two different types of wavenumber;
The Spatial Wavenumber or also called as spatial frequency is referred to as the number of wavelengths per unit distance. Angular wavenumber is generally used in physics and geophysics. Fundamentally, the equations for both angular and spatial wavenumber are the same except the fact that the angular wavenumber uses 2π in its numerator as this is the number of radians in a complete circle (that is 180 x 2 = 360°).
The Angular Wavenumber is also termed as circular wavenumber gives us the number of radians (a measure of angle) per unit distance. Spatial wavenumber is generally used in chemistry.
Waves can define sound, light, or the wavefunction of given particles, but each wave has a wavenumber.
Theoretically, the wavenumber is also termed as propagation number or angular wavenumber is referred to as the number of the complete cycle of a wave over its wavelength. It is denoted as a scalar quantity and is represented by the symbol k and the mathematical depiction is as follows:
k=1/λ
Where,
• k represents the wavenumber
• λ represents the wavelength
Wavenumber Formula
Using the equation mentioned above to calculate the spatial wavenumber (ν)
ν = 1 / 𝜆
= f / v
Where,
𝜆 represents wavelength
f represents frequency
v represents the speed of the wave.
k = 2π / 𝜆
where
𝜆 = v/f
Thus
k = 2πf / v
This equation is used to calculate angular wavenumber (k).
Wavenumber Formula in Spectroscopy
Wavenumber is a term that is used in spectroscopy to describe a frequency that has been separated by the speed of light in a vacuum. The formula of Wave number in spectroscopy and chemistry fields is given as follows;
¯v¯ = 1/ λ = ω/ 2πc = v/ c
Where,
¯v¯represents the spectroscopy wavenumber.
Λ represents the wavelength often called as spectroscopic wavenumber
Thus,
ω= 2 πv is the angular frequency
Spectroscopic wavenumber can also be converted into energy per photon by using Planck’s relation as given below;
E = hcv¯
Where
E represents the energy per photon
h represents the reduced Planck’s constant = 6.62607004 × 10-34 m2 kg / s
c represents the speed of light
v¯ represents the Spectroscopic Wavenumber
Spectroscopic wavenumber can also be converted to the wavelength of light as mentioned below;
λ (1n/v¯)
Where,
λ represents the wavelength
n represents the refractive index of the medium
v¯represents the Spectroscopic Wavenumber
The SI unit of measurement of Spectroscopic Wavenumber is often expressed as the reciprocal of meter that is written as m-1.
• The CGS unit of measurement of Spectroscopic Wavenumber is often expressed as the reciprocal of a centimeter that is written as cm-1.
Wavenumber Formula for Wave Equations
The formula for wave number in theoretical physics is given by
k = 2π/λ = ω/vp
Where;
k represents the angular wavenumber
λ represents the wavelength
ω = 2πv represents the angular frequency
When an electromagnetic wave propagate at the speed of light or c in a vacuum, then the wave equation k is represented as follows;
k =E/hc
Where,
k represents the angular wave number
E represents the energy of the wave
h represents the Planck’s constant which is equal to 6.62607004 × 10-34 m2 kg / s
c represents the speed of light
Applications of Wavenumber
• A wavenumber helps to calculate the spatial frequency.
• Apart from spatial frequency, wavenumber is also used to explain other quantities for example optics and wave scatterings in physics.
• Wavenumbers and wave vectors are often used to explain in X-ray diffraction and neutron diffraction, electron diffraction, and also in elementary particles in physics.
• Group velocity can also be explained with the help of a wavenumber.
Wavenumber Examples
Example 1: Calculate the Angular Wavenumber if the W wvelength of the Light wave is given as 500 Nanometers.
The formula for angular wavenumber is as follows;
k = 2π/λ
Where,
λ represents the wavelength of the light wave and is given as 500 nanometers which is further equal to 500 × 10-9 m.
[we know that 1nm =10−9m]
Now substituting the values in the formula to get the angular wavenumber as follows:
k = 2π/500×10−9
Thus,
k = 12.56 x 106 m-1
Example 2: Calculate the wavelength, frequency, and wavenumber of a light wave whose time period is given as 5.0×10−10 s.
The frequency or represented by symbol v of the light wave is given by;
1/ period = 1 / 5.0×10−10 seconds = 2×109 hertz or Hz
The wavelength of the light wave is given by;
c/v = 3×108 m / 2×109/s = 15×10−2 m. ( c is the speed of light)
The wavenumber of the light wave is given by;
νˉ= 1/λ= 1/ 15.0×10−2 =6.6 /m
Example 3: Calculate the frequency and wavenumber of radiation with wavelength 380 nm.
Given that; wavelength or
λ = 380nm = 380×10−9m [ we know that 1nm=10−9m]
Speed of light or c = 3×108 m/sec
Thus the Frequency (v) is given as,
v = c/ λ = 3×108 ms-1 / 380×10−9m
= 7.89 × 1014 hertz or Hz.
Wavenumber Citations
- Linear-in-wavenumber actively-mode-locked wavelength-swept laser. Opt Lett . 2020 Oct 1;45(19):5327-5330.
- Frequency-wavenumber domain analysis of guided wavefields. Ultrasonics . 2011 May;51(4):452-66.
- Wavenumber selection method to determine the concentration of cocaine and adulterants in cocaine samples. J Pharm Biomed Anal . 2018 Apr 15;152:120-127.
Share
Similar Post:
-
Absorption Spectra: Definition, Properties, and Examples
Continue ReadingAbsorption Spectra Definition
Atomic spectra is referred to as the study of atoms (and their atomic ions) through their interaction with electromagnetic radiation. When a beam of light travels from one medium to another, it either bends in the direction of the normal or away from the normal. The speed of light is thus dependent on the nature of the medium through which it passes.
Absorption Spectra Characteristics
• It was observed that when a ray of white light falls on a prism it usually experience refraction twice. First, when it travels from the rarer medium (that is air) to a denser medium (that is glass) and secondly when it passes from the denser medium (that is glass) to a rarer medium (that is air).
• Lastly, a band of colours is observed, commonly termed as a spectrum, which is formed out of a ray of white light. On observing this spectrum more thoroughly, it was seen that the colour having a smaller wavelength deviates the most and vice versa.
• Therefore, a spectrum of colours is seen which ranges from the colour red to violet, where the red colour having the longest wavelength deviates the least. This kind of spectrum is often termed a continuous spectrum.
• The spectrum of the electromagnetic radiation released or absorbed by an electron during its transitions between different energy levels in an atom is termed as atomic spectra.
Types of Atomic Spectra
There are three types of atomic spectra as given below;
Emission Spectra
Absorption Spectra
Continuous Spectra
Spectra and Spectroscopy
Spectrum is broadly used in the field of optics and in many other fields. Spectrum displays a varied range of wavelengths having different frequency radiations. A rainbow is referred to as a spectrum that contains different wavelengths of light. The spectrum of light formed from the rainbow is generally referred to as VIBGYOR.
A spectroscope or Spectrograph is the device that is used to separate the radiations of different wavelengths. A spectrometer is a scientific instrument that helps to separate and measure spectral components of this physical phenomenon. Spectroscopy is the branch of science that generally deals with the study of the spectrum.
Classification of Spectra
Spectra is categorized into two types as mentioned below:
• Emission spectra
• Absorption spectra
i. Emission Spectra
The emission spectrum is commonly formed by the radiation emitted or produced by an electron in the excited molecules or atoms and this is termed as the emission spectrum. When an atom or molecule absorbs energy, then the electrons are excited to a higher energy level and when the electron falls back to its lower energy level, light is emitted or produced, which generally has the energy equivalent, to the difference between higher and the lower states energy.
Due to the availability of numerous states of energy, an electron thus can undergo many transitions, each transition gives rise to a unique wavelength that encompasses the emission spectrum. The emission spectrum is thus formed by the frequencies obtained from these emitted light.
Based on the source, the emission spectrum is further categorized into;
a) Continuous Spectrum: When the spectrum has no breaks or openings between their wavelength range then this type of spectrum is termed as a continuous spectrum. For instance; A rainbow.
b) Line Spectrum: When the spectrum has a discrete or distinct line that is atoms emit light only at specific wavelengths with dark spaces between them, then this type of spectrum is termed as a line spectrum. For instance; Hydrogen line spectrum.
Absorption Spectra
This kind of spectrum is created by the frequencies of light that is transmitted with dark bands when energy is absorbed by the electrons generally in the ground state to reach higher energy level states. This is the kind of spectrum that is produced when atoms absorb energy.
When light from any source is passed through the chemical solution, then a pattern comprising of dark lines is observed. This pattern is further analysed with the help of a spectroscope.
The dark line pattern is seen precisely in the same place where coloured lines in the emission spectrum were observed. The spectrum hence attained is termed as the absorption spectrum.
Emission spectra, unlike absorption spectrum, emit all the colours in an electromagnetic spectrum, whereas few colours in the absorption spectrum may be absent due to the redirection of absorbed photons.
Absorption Spectroscopy
Absorption spectroscopy is referred to as a spectroscopic technique that is used for measuring the absorption of radiation when it interacts with the sample.
Absorption spectroscopy is linked to the absorption spectrum because the sample thus used interacts with photons produced from the radiating field.
Applications Absorption Spectroscopy
a) Chemical Analysis: The numerical nature of absorption spectroscopy makes it a perfect choice for chemical analysis. The absorption spectrum of the different compounds can be differentiated from one another using absorption spectroscopy. This is only possible because of the specificity nature of the absorption spectrum.
b) An application of absorption spectroscopy is an infrared gas analyser that is often used for detecting the pollutants present in the air or atmosphere. It also helps to distinguish between pollutants from nitrogen, oxygen etc.
c) Remote Sensing: Absorption spectroscopy is also used for analytical purposes such as for measuring the presence of dangerous elements.
Emission Spectra vs Absorption Spectra
The key difference between emission and absorption spectra is that an emission spectrum consists of different coloured lines, however, an absorption spectrum consists of dark-coloured lines in their spectrum. Other differences between absorption and emission spectrum are mentioned below;
Emission Spectra Absorption Spectra The emission spectrum is formed when atoms release energy Absorption Spectra is formed when atoms absorb energy Generally comprises of coloured lines in the spectrum Generally comprises of dark lines or gaps in its spectrum The type of photons emitted from the emission spectrum is used in estimating the different kind of elements from which a substance is made as each element emits different amount of energy and generally has a unique emission level. The wavelengths of light absorbed is used in calculating the number of substances that is present in the sample Absorption Spectra Citations
- Basic aspects of absorption and fluorescence spectroscopy and resonance energy transfer methods. Methods Cell Biol . 2008;84:213-42.
- UV-VIS absorption spectroscopy: Lambert-Beer reloaded. Spectrochim Acta A Mol Biomol Spectrosc . 2017 Feb 15;173:965-968.
- Absorption spectroscopy. Methods Enzymol . 2011;500:59-75.
Share
Similar Post:
-
Balmer Series: Definition, Equation, and Examples
Continue ReadingBalmer Series
Balmer spectral series was initially noticed by Johann Balmer during the years 1885, Therefore the series is named after him that is the balmer series. Balmer series is exhibited when an electron shift takes place from higher energy states (that is ni =3,4,5,6,7,…) to lower energy states that are nf = 2 energy states.
The wavelength of the Balmer series generally falls in the visible part of the electromagnetic spectrum( having wavelength 400nm to 740nm) or is abbreviated as EM spectrum. In astronomy, the existence of Hydrogen is noticed by using the H-Alpha line of the Balmer series.
Balmer Series Formula
In the year 1885, based on experimental observations on the hydrogen atom, Balmer advised the formula for linking the wavenumber of the spectral lines emitted to the energy shells involved in an electron shift. This formula is given as:
λ = C(m2/m2-n2)
Here, λ represents the observed wavelength
C represents a constant (364.50682 nm)
n represents the lower energy level = 2, and m represents the higher energy level, which commonly has a value greater than 3.
The above observation was further refined by Johannes Rydberg, where R represents the Rydberg constant.
1/λ = R ((1/nf2) – (1/ni2))
According to the Balmer series, nf is always equal to 2. This equation was hence combined with the Bohr model to analyze the energy that is needed to shift an electron between its initial energy level and final energy levels.
ΔE = Rhc ((1/nf2) – (1/ni2))
Paschen Series (nf = 3): The series was initially noticed during the years 1908, by a German physicist named Friedrich Paschen. The Paschen series is exhibited when electron transition takes place from higher energy states (that is ni =4,5,6,7,8,…) to lower energy states that is nf =3 energy state. The wavelength of the Paschen series generally falls in the Infrared region of the electromagnetic spectrum.
Brackett Series (nf = 4): The series was initially noticed during the years 1922, by a famous American physicist Friedrich Sumner Brackett. Brackett series is exhibited when electron shift takes place from higher energy states (that is ni =5,6,7,8,9…) to lower energy state that is nf =4 energy state. The wavelength of the Brackett series generally falls in the Infrared region of the electromagnetic spectrum.
Pfund Series (nf = 5): The series was initially noticed during the years 1924, by a famous scientist named August Harman Pfund. Pfund series is exhibited when an electron shift takes place from higher energy states(that is ni = 6,7,8,9,10,…) to nf=5 energy state. The wavelength of the Pfund series usually falls in the Infrared region of the electromagnetic spectrum.
The Bohr Model
In 1913, Niels Bohr a famous scientist and chemist proposed a model for the hydrogen atom having the atomic number 1. He stated that the electrons present in an atom revolve around the nucleus in discrete paths called orbit or an energy shell. The electron while in its stationary or its rest state cannot produce energy, but can only absorb energy when it moves from one orbit to another orbit.
The quantum number, abbreviated as n is used to designate the different energy states. The lowest energy state is termed as the ground state, in which n is always equal to one. The excited states are further equal to 2, 3, 4, and so on. When the electron present at the ground state absorbs energy which is equivalent to the difference between the ground state of the electron and the second state the electron by absorbing a photon. The electron thus turns out to be more excited and displays transitions from the ground state to the n= 2 excited states.
According to Bohr, the potential energy (P.E) of an electron present in the nth level is measured by using the following equation mentioned below:
En = -(Rhc/n2)
where En represents the potential energy,
R represents the Rydberg constant which is equal to 1.0974 × 107 m-1
h represents Planck’s constant which is equal to 6.62607004 × 10-34 m2·kg/s),
c represents the speed of light (~ 3 × 108 m/s).
The electrons can also spontaneously return to the ground state or any other lower excited state. When this happens, then some amount of energy is produced can be depicted in the form of the emitted photon. The energy of the photon is thus always equal to the energy difference between the higher and lower energy states. Subsequently, different types of atoms have different energy levels and the light emitted from each transition varies for every atom.
Hydrogen Spectrum
As it is now known that electrons in an atom or a molecule absorb energy and become excited, and then they transfer themselves from a lower energy level to a higher energy level, and radiation or energy is released when they come back to their original ground states. This great phenomenon is also the same for the emission spectrum through hydrogen atom as well , and therefore it is termed as the hydrogen emission spectrum.
The Hydrogen Atom
The hydrogen atom is referred to as the simplest atomic system that is found in nature, therefore it produces the simplest of these series. When the beam of light or radiation is allowed to enter the device via a slit, then each distinct component of the light or radiation can be depicted in the form of images of the source. These images are pictured when resolved under the spectroscope. The images received will be in the form of parallel lines that are organized next to each other with consistent spacing. The lines seen will be apart in the higher wavelength side and then they come closer progressively when shifted from higher to lower wavelength side. The shortest wavelength will thus hold the least spaced spectral lines.
Rydberg Formula
The wavelengths of the spectral series are commonly calculated by using the Rydberg formula.
Scientifically, it can be expressed as-
1/λ = R ((1/n2f – (1/n2f))
Where,
• 𝜆 represents the wavelength
• R represents the Rydberg constant has the value 1.09737✕107 m-1
• Z represents the atomic number of an atom
• ni represents the lower energy level
• nf represents the higher energy level
Note: This equation mentioned above is valid only for Hydrogen and Hydrogen like elements.
Lyman series (nf =1)
This spectral series was projected during the years 1906-1914, by the famous scientist Theodore Lyman. According to Bohr’s model, the Lyman series is exhibited when electron shift takes place from higher energy states (that is ni = 2,3,4,5,6,…) to nf =1 energy state. The wavelength of the Lyman series generally falls in the Ultraviolet band.
Balmer Series Citations
- Measurements of aluminum and hydrogen microplasma. Appl Opt . 2007 Jul 1;46(19):4026-31.
- Measurement of the deuterium Balmer series line emission on EAST. Rev Sci Instrum . 2016 Nov;87(11):11D616.
- Balmer series Hbeta measurements in a laser-induced hydrogen plasma. Appl Opt . 2003 Oct 20;42(30):5992-6000.
Share
Similar Post:
-
Electromagnetic Radiation: Definition, Properties, and Examples
Continue ReadingElectromagnetic Radiation
Electromagnetic radiation is a spectrum that consists of radio waves, microwaves, infrared waves, visible light, ultraviolet radiation, X-rays, and gamma rays.
Electromagnetic radiation has a particle as well as a wave nature therefore this makes it interesting to study its nature in quantum theory.
Electromagnetic Radiation Properties
• The oscillating charged particles creates an oscillating electric and magnetic fields which are perpendicular or right angles to each other and both are perpendicular to the direction of propagation of the wave as well.
• Electromagnetic waves generally do not require a medium which means that they can travel in a vacuum.
• There are numerous types of electromagnetic radiation, that differ from one another in terms of their wavelength or frequency.
• Electromagnetic radiation is commonly categorized based on several properties such as frequency, wavelength, amplitude etc.
Electromagnetic Radiation Formula
Frequency is referred to as the number of waves that passes through a given point in one second. A general equation that is related to the speed of light, frequency, and wavelength of electromagnetic radiation is as follows:
c = ν 𝝀
Where,
• c represents the speed of light
• ν represents the frequency of the electromagnetic wave
• 𝝀 or lambda represents the wavelength of the electromagnetic wave.
Apart from the above-mentioned parameters frequency and wavelength, some other factors are also used to classify electromagnetic radiation. One of these factors is the wavenumber. Scientifically, the wavenumber is equal to the reciprocal of the wavelength. It is represented in the SI unit as m.
ν = 1/Wavelength
Dual Behaviour of Electromagnetic Radiation
Electromagnetic Radiation was assumed to have a wave nature only thus with the help of wave nature we can clearly explain a phenomenon like interference and diffraction. But Wave nature of Electromagnetic Radiation was unable to describe few things such as Black body radiation & the photoelectric effect.
In 1900, Planck stated the quantum theory and was successful in explaining blackbody radiation. According to this theory, atoms or molecules release or absorb energy only in discrete amounts termed as quantum. Quantum is referred to as the smallest amount of energy that is absorbed or released in the form of electromagnetic radiation.
Further, Einstein explained the Photoelectric effect by using Planck Quantum theory. He proposed that when a photon falls on the surface of a metal, then the complete photon’s energy is transferred to the electron.
Now based on the above observations of both Planck Quantum theory & Einstein Theory of Photoelectric effect, it was found that Electromagnetic Radiation behaves like particles or photons as well. Now the particle nature was not much reliable with the known wave nature of light. Consequently, this caused striking confusion among the scientists. The only solution to this problem was to accept the dual nature of Electromagnetic Radiation.
Thus, electromagnetic radiation posses dual nature;
Wave Nature
Particle Nature
Particle Nature of Electromagnetic Radiation
i. Photoelectric Effect
The photoelectric effect is referred to the emission of electrons when electromagnetic radiation, such as light, hits a substance. Electrons emitted in this effect are termed as photoelectrons. Though, this phenomenon of photoelectric effect can be explained only by the particle nature of light, in which light can be pictured as a stream of particles of electromagnetic energy. These particles of light are termed as photons.
Photons are explained below;
• Photons are elementary particles. It is referred to as a quantum of light.
• The energy of a photon is , E = hf Where h represents Planck’s constant F represents wave frequency E represents photon energy
• A photon generally remains unaffected by electric and magnetic fields. Photon is electrically neutral in nature.
• A photon is massless that is it has zero mass.
• Photons, unlike atoms can be formed or destroyed when radiation is produced or absorbed.
ii. Black Body Radiation
When the black body is heated, it becomes red-hot. In simple words, it releases red coloured light. When the temperature is increased further, then the colour of the radiation emitted changes as follows, first from red to yellow then to white and lastly to purple as the temperature increases. This states that the wavelength of radiation produced by the black body decreases with a rise in temperature.
Wave Nature of Electromagnetic Radiation
Wave theory of radiation was unable to explain the phenomena of the photoelectric effect and also the black body radiation.
Major points of electromagnetic wave theory include;
The energy that is emitted from a source is in the form of radiation and is also termed as radiant energy. These radiations comprise of electric and magnetic fields which oscillate perpendicular (or at right angles ) to each other and also is perpendicular to the direction of propagation of radiation.
These radiations or electromagnetic radiations (or electromagnetic waves) travel with the velocity of light and also possesses wave character.
Characteristics of a wave:
• Wavelength: The wavelength of a wave is referred to as the distance between two consecutive crest or trough It is represented by a symbol lambda ( 𝝀 ) and is generally expressed in cm or m.
• Frequency: The frequency of a wave is referred to as a number of waves that passes through a point in one second It is represented by a symbol v (nu) and is generally expressed in its SI unit that is hertz or abbreviated as Hz.
• Velocity: The velocity of a wave is referred to as the linear distance which is travelled by a wave in one second It is represented by a symbol v and is commonly expressed in centimetre per second or metre per second (cm/sec or m/sec).
• Amplitude: The amplitude of a wave is referred to as the height of the crest as well as the depth of trough true It is generally represented by symbol a and is expressed in the metre , centimetre or the units of length.
• Wavenumber: Wavenumber is referred to as the number of waves that is present in 1 cm length.
Electromagnetic Radiation Citations
Share
Similar Post:
-
Atomic Model: Definition, Properties, Types, and Examples
Continue ReadingAtomic Model
Atomic structure is defined as the structure of an atom containing a nucleus present in the center in which the protons or positively charged particles and neutrons (neutral) are present. The negatively charged particles are termed as electrons and they revolve around the nucleus.
In the 1880s, the first scientific theory of atomic structure was explained by John Dalton. A variety of different models have been evolved over the past decades to understand the functions of an atom. As a result, there are five basic atomic models which helped us to describe and comprehend the structure of the atom. Each of these models mentioned below had its own advantages and drawbacks.
The five atomic models that shaped the modern atomic theory are:
• John Dalton’s atomic model
• J.J. Thomson’s atomic model
• Ernest Rutherford’s atomic model
• Niels Bohr’s atomic model
• Quantum Numbers/model
I. Dalton Atomic Model
The English chemist and scientist named John Dalton stated that all matter is made up of atoms, which are undividable. He also proposed that all the atoms present in an element are the same, but the atoms of different elements generally differ in their size and mass. The following are the postulates of Dalton’s theory;
• All matter is made up of particles called atoms.
• Atoms are indivisible particles.
• Specific elements generally have only one type of atom present in them.
• Each atom has a constant mass respectively that differs from element to element.
• Atoms can neither be formed nor can be destroyed but can be transformed from one form to another.
Drawbacks of Dalton Atomic Model:
• The theory was not able to describe the existence of isotopes.
• Dalton’s atomic theory does not explain the existence of subatomic particles. Dalton’s atomic theory projected that the atoms were indivisible. However, the discovery of subatomic particles (for example, protons, electrons, and neutrons) disproved this postulate.
• Dalton’s atomic theory failed to explain isobars( two different elements having the same mass number. For Instance: 40Ar and 40Ca)
II. Thomson Atomic Model
The English chemist and scientist Sir Joseph John Thomson described the structure of the atom in the early 1900s.
He was awarded the Nobel prize later for the finding of “electrons”. His work is chiefly based on an experiment titled a cathode ray experiment. The working of this experiment is as follows:
Cathode Ray Experiment: It has a tube made of glass which further has two openings, one opening is for the vacuum pump and the other one is for the inlet through which a gas is pumped.
A high voltage electric current is passed through a discharge tube that contains gas at a very low pressure, a green glow is thus seen at the other end of the discharge tube. This green glow or fluorescence observed is the result of the rays which are released from the cathode towards the anode. These rays are termed as cathode rays.
Conclusions: Based on this observation from his cathode ray experiment, Thomson defined the atomic structure as a positively charged sphere that contains negatively charged particles called electrons.
It is usually stated as the “plum pudding model” because it can be pictured as a plum pudding dish where the pudding represents the positively charged atom and the plum pieces in it represent the electrons.
Drawbacks of Thomson’s Atomic Model: The theory did not mention anything about the nucleus present in the center of an atom.
III. Rutherford Atomic Model
Rutherford, a famous scientist revised the structure of an atom with the discovery of another subatomic particle named as a Nucleus. His atomic model is built on the Alpha ray scattering experiment.
Alpha Ray Scattering Experiment Structure:
• Rutherford took a gold foil as he wanted a fragile layer.
• In this experiment, fast-moving alpha particles were bombarded on a thin gold foil.
• Alpha particles are referred to the helium ions with a +2 charge and thus have a significant amount of energy.
• Rutherford predicted that the alpha particles would pass through the gold foil but some of the particles deflected and striked the fluorescent screen.
Conclusions:
• Since most of the rays passed straight through the gold foil, Rutherford thus observed that most of the space inside the atom is vacant or empty.
• Few rays which got reflected is because of the repulsion with some other positive charge present inside the atom.
• 1/1000th of rays got forcefully deflected because of the presence of a very strong positive charge confined in the center of the atom. He named this strong positive charge as “nucleus”.
• He stated that most of the charge and the mass of the atom is present in the center (Nucleus).
Rutherford’s Structure of Atom Based on the above comments and assumptions, Rutherford projected his own atomic structure which is;
• The nucleus is present at the center of an atom, generally where most of the charge and mass of the atom is concentrated.
• Electrons revolve around the nucleus (which is present in the center) in circular paths called orbits, just like the planets revolve around the sun.
Limitations of Rutherford Atomic Model:
• If electrons present in an atom revolve around the nucleus, then they have to spend energy, as a result, a lot of energy will be spent by the electrons, and ultimately, electrons will lose all their energy and will fall into the nucleus thus Rutherford was unable to explain the stability of atoms.
IV. Bohr Atomic Model
Neils Bohr model is the most widely used atomic model which helped to define the atomic structure of an element that is built on Planck’s theory of quantization. Bohr’s Postulates:
• The electrons present inside the atoms are positioned in discrete orbits termed as “stationary orbits”.
• The energy levels of these shells can be denoted as quantum numbers.
• Electrons can travel to higher levels by absorbing energy and can also move to lower energy levels by emitting or releasing their energy.
• When an electron stays in its rest or stationary form, then there will be no absorption or release of energy.
Drawbacks of Bohr’s Atomic Model:
• Bohr’s atomic structure is applicable only for single-electron species. For instance; H, He+, etc.
• Bohr’s theory was unable to explain both Stark and Zeeman’s effects.
V. Quantum Numbers
• Principal Quantum number (n): It represents the orbital number or the shell number of the electron.
• Azimuthal Quantum numbers (l): It represents the orbital (sub-orbit) of the electron.
• Magnetic Quantum number: It represents the number of energy states present in each orbit.
• Spin Quantum number(s): It represents the direction of spin, that is when S = -½ the spin of an electron is Anticlockwise and ½ then the spin of an electron is Clockwise.
Electronic Configuration of an Atom:
The electrons are usually filled in the s, p, d, f orbits as per the following rule; 1.
Aufbau’s principle: The filling of electrons must take place by following the ascending order of the energy orbitals that is;
• Initially, the lower energy orbital should be filled and then the higher energy levels.
• Ascending order of energy orbitals is as follows 1s, 2s, 2p, 3s, 3p, 4s, 3d, and so on. 2.
Pauli’s exclusion principle: this principle states that no two electrons can have all the four quantum numbers mentioned above to be the same or similar.
NOTE: If two electrons are positioned in the same energy state then they should be positioned with opposite spines.
Atomic Model Citations
- Nagaoka’s atomic model and hyperfine interactions. Proc Jpn Acad Ser B Phys Biol Sci . 2016;92(4):121-34.
- Dalton’s disputed nitric oxide experiments and the origins of his atomic theory. Chemphyschem . 2008 Jan 11;9(1):106-10.
- Atomic Theory and Multiple Combining Proportions: The Search for Whole Number Ratios. Ann Sci . 2015 Apr;72(2):153-69.
Share
Similar Post:
-
Millikan Oil Drop Experiment: Definition, and Examples
Continue ReadingMillikan Oil Drop Experiment Definition
In this experiment, Millikan permitted the charged tiny droplets of oil to pass through a hole into an electric field. Then, by changing the strength of the electric field, the charge over an oil droplet was calculated, which always results as an integral value of ‘e.’
What is Millikan Oil Drop Experiment?
Millikan oil drop experiment is accomplished by Millikan and Harvey Fletcher in 1909 to measure the charge of an electron. This experiment proved to be helpful in the physics community.
Robert Andrews Millikan was a famous American physicist and was awarded the Nobel Prize for Physics in 1923 for his work on the elementary electronic charge and the photoelectric effect.
In 1909, Millikan performed a series of experiments to find the electric charge which is carried by an electron. He initially began his experiment by measuring the path of charged water droplets in an electric field. The results projected that the charge present on the droplets is a simple multiple of the basic electric charge, but the test’s result was not precise enough to be considerable.
To obtain more specific results, in 1910 he performed his famous oil-drop experiment in which he substituted water (which tends to evaporate quickly) with oil, and this experiment is further explained below;
Millikan Oil Drop Experiment Apparatus
The apparatus for the experiment was created by Millikan and Fletcher. It is consists of two metal plates that are held at some distance by an insulated rod. Four holes were made in the plate, out of which three were only allowed to pass the light through them and the fourth one is used to view through the microscope.
Ordinary oil was not used for this experiment as it tends to evaporate by the heat of the light and therefore an error could be caused in Millikan Oil Drop Experiment. So, the oil having low vapor pressure was used, the same that is used in a vacuum apparatus.
• A specific type of oil as mentioned above is sprayed into the chamber, where the drops attain electrical charge.
• The droplets are then allowed to enter the space present between the plates and, as they were charged, they could be effortlessly controlled by altering the voltage across the plates.
• Mainly, the oil drops were allowed to fall between the plates having no electric field. They then rapidly reached terminal velocity due to the presence of friction of the air in the chamber.
• The field was then turned on and it was huge enough, thus some of the drops started to rise. This is because of the presence of upwards electric force, (FE) on them which is greater than the downwards gravitational force, g.
• Millikan’s experiment was actually meant to have the drops to fall at a constant rate. At this constant rate, the gravitational force present on the drop and the force of the electric field or upwards electric force on the drop is equal.
• Millikan then repeated this same experiment for over 150 oil drops out of which he selected 58 oil drops results and then with the help of these observations he determined the highest common factor.
Millikan Oil Drop Experiment Calculation
As mentioned above,
Fup = Fdown
Fup = Q. E
Fdown = m.g
Where, Q represents an electron’s charge
E represents the electric field
m represents the droplet’s mass, and
g represents gravity.
Q⋅E = mg
Therefore,
Q = mg /E
It can be said that an electron charge is measured by Millikan. Millikan stated that all drops had charges that were equal to 1.6x 10-19 C multiples.
Millikan Oil Drop Experiment Conclusion
The charge present on an oil droplet is always equal to an integral value of e (1.6 x 10-19). Hence, the assumption of Millikan’s Oil Drop Experiment displays that the charge is quantized, that is the charge present on any particle is always be an integral multiple of e.
Millikan’s oil drop experiment was a vibrant demonstration of the quantization of charge.
The experiment has since been commonly conducted by many physics undergraduates, though it is quite expensive and to get the precise result is quite difficult.
Millikan Oil Drop Experiment Importance
Millikan’s experiment is quite crucial to study because it establishes the charge over an electron.
Millikan used a simple device in which he adjusted the actions of electric, gravitational, and air drag forces.
With the help of the apparatus, he was successful in estimating the charge on an electron that is equal to 1.60 × 10-19 C.
Reason for Using Oil Drops
Oil drops are used in Millikan oil-drop experiment because oil drops usually retain their mass over some time when it is exposed to higher temperatures. Likewise, he used an atomizer for ultra-fine droplets. Therefore, he preferred oils over water because water changes its state or form at much higher temperatures.
Furthermore, it is extensively known that oil tends to retain the exact volume, omass, and weight. This property of oil enabled him to have a precise measurement of the charge. Other liquids present in nature may separate, disintegrate or evaporate.
Millikan Oil Drop Experiment Citations
- Millikan recharged. Nature Physics volume 8, page106 (2012)
- Millikan “oil drop” stabilized by growth. Science . 1979 Jan 26;203(4378):353-4.
- Performing the Millikan experiment at the molecular scale: Determination of atomic Millikan-Thomson charges by computationally measuring atomic forces. J Chem Phys . 2017 Oct 28;147(16):161726.
Share
Similar Post:
-
Electromagnetic Waves: Definition, Properties, and Examples
Continue ReadingElectromagnetic Waves Definition
Electromagnetic radiation involves electromagnetic waves, which are coordinated oscillations of both electric and magnetic fields. It can further be said that electromagnetic waves are the composition of oscillating electric and magnetic fields.
Electromagnetic radiation or electromagnetic waves are produced due to periodic change of electric or magnetic field. In a vacuum or void, electromagnetic waves generally travel with the speed of light which is represented as c.
1. The position of an electromagnetic waves present within the electromagnetic spectrum can be categorized by its frequency of oscillation or wavelength.
2. Some sources of electromagnet radiation include; the cosmos (for instance – the sun and stars), radioactive elements, and manufactured devices.
3. EM displays a dual wave and particle nature.
What is Electromagnetic Waves?
Electromagnetic radiations are produced when an atomic particle, such as an electron, is accelerated and is moved by an electric field. This movement produces oscillating electric and magnetic fields, which are at right angles or 90 degrees to each other and usually travel in a bundle of light energy termed as photons.
A wavelength is defined as the distance between two consecutive troughs (peak) of a wave. This distance is commonly measured in meters (m).
Frequency is referred to as the number of waves formed in a given period of time. It is generally measured in hertz (Hz).
Mathematical Representation of Electromagnetic Wave
In the electromagnetic wave, E is referred to as the electric field vector and B is defined as the magnetic field vector.
Therefore, the direction of propagation of the electromagnetic wave is thus given by vector cross product of the electric field and magnetic field. It is shown below: E→×B→
Graphical Representation of Electromagnetic Waves
Electromagnetic waves are commonly shown by a sinusoidal graph. It comprises of time-varying electric and magnetic fields which are perpendicular or at right angles to each other and are also perpendicular (right angles) to the direction of propagation of waves. The uppermost point of the wave is named as crest whereas the lowest point is termed as a trough. The waves travel at a fixed velocity of 3 x 108 m.s-1 in vacuum.
The Electromagnetic Spectrum
EM radiation spans a widespread range of wavelengths and frequencies. This range is termed as the electromagnetic spectrum. The EM spectrum is usually divided into seven regions, based on decreasing wavelength and increasing energy and frequency. The common terms are: radio waves, microwaves, infrared (IR), ultraviolet (UV), X-rays, gamma rays and visible light. Normally, lower-energy radiation such as radio waves, is represented in frequency and microwaves, infrared, visible and UV light are generally expressed as wavelength and higher-energy radiation, like X-rays and gamma rays are stated in energy per photon.
Radio Waves
Radio waves has the lowest range of the EM spectrum, with frequencies equal to 30 gigahertz (GHz), and wavelengths of 10 millimetres or 0.4 inches.
Uses: Radio waves are used mainly for communications including voice, data, and entertainment media.
Microwaves
Microwaves lie in between the EM spectrum of radio and infrared waves. They have frequencies from about 3 GHz up to about 30 trillion hertz, or 30 terahertz (THz), and wavelengths of 10 mm (0.4 inches) to 100 micrometres (μm) or 0.004 inches.
Uses: Microwaves are commonly used for high-bandwidth communications, radar and is also used as a heat source for microwave ovens and industrial applications.
Infrared
Infrared is in the range of the EM spectrum that lies between microwaves and visible light. IR express frequencies from 30 THz up to about 400 THz and wavelengths of about 100 μm (0.004 inches) to 740 nanometres (nm), or 0.00003 inches.
Uses: IR light is generally invisible to naked eyes, but if the intensity is enough, then it can be felt as heat.
Visible Light
Visible light lies in the middle of the infrared and ultraviolet waves of EM spectrum. It displays the frequencies of around 400 THz to 800 THz and wavelengths of nearly 740 nm (0.00003 inches) to 380 nm (.000015 inches).
Uses: visible light can be referred to as the wavelengths which are visible to naked eyes.
Ultraviolet
Ultraviolet light lies in the range of the EM spectrum between visible light and X-rays. Its frequencies are around 8 × 1014 to 3 × 1016 Hz and wavelengths of about 380 nm (.000015 inches) to about 10 nm (0.0000004 inches).
Uses: UV light is referred to as a constituent of sunlight; though, it is not visible to the naked eye. These radiations further have several medical and industrial applications.
• These rays are germicidal in nature, kills bacteria, viruses and moulds present in the air, water and on surfaces.
• It is also used to spot phony bank notes, as these fakes notes turn fluorescent in colour under UV light whereas real notes don’t turn fluorescent under the UV light.
X-rays
X-rays are widely classified into two types, soft X-rays, and hard X-rays. Soft X-rays have the range that lie between UV and gamma rays. Soft X-rays have frequencies of about 3 × 1016 to 1018 Hz and wavelengths of about 10 nm (4 × 10−7 inches) to 100 picometers (pm), or 4 × 10−8 inches. Hard X-rays further reside in the same region of the EM spectrum as gamma rays. The only difference between them is; X-rays are produced by accelerating electrons, whereas gamma rays are formed by nuclei of atom.
Uses: The most vital use of X-rays is that it is used to detect bone fracture.
Gamma-rays
Gamma-rays generally have frequencies greater than 1018 Hz and wavelengths less than 100 pm (4 × 10−9 inches).
Uses: Gamma radiation damage the living cells and tissues, which is beneficial for killing of cancer cells in small doses. But it is tremendously hazardous to humans in uncontrolled amount.
Electromagnetic Waves Citations
- Benefits and hazards of electromagnetic waves, telecommunication, physical and biomedical: a review. Eur Rev Med Pharmacol Sci . 2019 Apr;23(7):3121-3128.
- Electromagnetic radiation. Br Med Bull . 2003;68:157-65.
- Effect of electromagnetic waves on human reproduction. Ann Agric Environ Med . 2017 Mar 31;24(1):13-18.
Share
Similar Post:
-
Endemic: Definition, Meaning, and Examples
Continue ReadingEndemic Definition
Endemic refers to the quality of an item, location, or notion that is unique to that area or region. The term is used to describe a species that flourishes in a certain location and is not often seen elsewhere. Endemism is a similar term (n., def: the state of being endemic). Another term for endemicity is “the property of being endemic.”
The word endemic comes from the Greek word endemos, which means “to dwell in a location.”
Definition of Endemic Species
The term endemic can refer to a species (ecology) or a disease in biology (medicine). In ecology, an endemic species is one that is unique to the area in which it is found. A species might be endemic to a limited geographic region, such as a single island, or a larger geographical area, such as a continent. If it’s present elsewhere, endemic isn’t the right word to use. The reverse of endemism, cosmopolitan distribution, occurs when a species is present in a wide range of habitats and geographic regions.
How do Species Become Endemic
Speciation is caused for a variety of reasons. Environmental pressure and geographic constraints are two examples of these variables. The types of animals and plants that may flourish and reproduce in a given region are determined by the environmental conditions that the species is exposed to, as well as the constraints imposed by the geographical position of the species’ habitat (e.g., a landmass surrounded by a large body of water). Ecuador’s islands, for example, are home to giant tortoises (big land tortoises). They were unable to relocate to distant islands due to the waters around the area. As a result, their population was limited to two secluded tropical island groups in Ecuador: the Seychelles’ Aldabra Atoll and Fregate Island, and Ecuador’s Galápagos Islands.
Endemic Species Examples
Animal and plant species that are unique to a certain geographic region are known as endemic species.
Endemic Animals
Endangered animals are those that can only be found in a small region. The following are some examples.
• Microlophus delanonis (Hood Lava Lizard) is indigenous to Punta Suarez, Espaola Island, Galapagos.
• The population of red squirrels is unique to the north of Scotland.
• Only the Isle of Man has a Manx cat.
• Madagascar’s lemur.
• In the Philippines, sinarapan is a kind of fish.
• New Zealand’s Tokoeka kiwi.
• Australia’s venomous devil lizard.
• The South East Asian tarsier.
• In Tasmania, there is a Tasmanian devil.
• In Hawaii, there is a Hawaiian hoary bat.
Endemic Plants
Plants that are only present in a small region are known as endemic. The following are some examples.
• Nevada primrose (Primula nevadensis) is a plant that is only found in the Great Basin Region in eastern Nevada.
• Aglaia ceramica is an endemic to Indonesia’s Maluku Islands.
• Cassine koordersii is a native of the Indonesian island of Java.
• Melica penicillaris is a grass indigenous to Turkey’s Inner Anatolia.
• Crocus aleppicus is a flowering plant species in the Iridaceae family that is only found in Israel.
• The Hawaiian hibiscus is a flowering plant that is endemic to Hawaii.
Endemic Disease
An endemic illness is one that is always present, in some form or another, in people of a given social class or in people who live in a certain region. Malaria, for example, is a sickness that is only seen in the tropics.
Endemic Citations
- Endemic Plant Species Conservation: Biotechnological Approaches. Plants (Basel) . 2020 Mar 9;9(3):345.
- A newly recognised Australian endemic species of Austrolecanium Gullan & Hodgson 1998 (Hemiptera: Coccidae) from Queensland. Zootaxa . 2017 May 26;4272(1):119-130.
- Global warming and extinctions of endemic species from biodiversity hotspots. Conserv Biol . 2006 Apr;20(2):538-48.
Share
Similar Post:
-
Desiccation: Definition, Meaning, and Examples
Continue ReadingDesiccation Definition
Desiccation is the condition, act, or process of completely eliminating or extracting all water content from the body, resulting in severe dryness.
Desiccation Etymology
“Desiccate” (v., def: to desiccate) and “desiccated” are two words that are related (adj., def: pertaining to desiccation or one that is dried by desiccation).
What is Desiccation?
Desiccation can be achieved by exposing the organism to a desiccant or a desiccator, for example. A desiccant is a chemical compound that works against humectants, which retain moisture in place. Desiccants include silica gel, activated charcoal, calcium chloride, and calcium sulphate, among others. By adsorbing moisture, they cause desiccation. A vacuum desiccator is a glass or plastic container used in the laboratory to help make or keep things dry.
Desiccation Definition in Biology
Desiccation is the process of an organism being dried out by eliminating water or extracting moisture. Drying crops (agriculture), drying newborn animals (particularly livestock animals), and killing sensitive organisms, such as some bacteria, are some of its biological uses.
Water molecules prefer to exit the cell through osmosis through the aquaporins on the cell membrane when there is no water surrounding it. The water subsequently evaporates and dissipates into the atmosphere. This is what happens when an aquatic creature is removed from its natural environment or when a susceptible organism is exposed to a desiccating substance, such as a salt-exposed earthworm.
Desiccation susceptibility varies. Desiccation resistance is high in many viruses. Some bacteria are not entirely resistant and may survive, allowing them to reactivate when water becomes available. Mycobacterium tuberculosis, for example, can live for several months.
Desiccation in Plants
Water is necessary for the survival of plants. Land plants, in particular, use their roots to take water from the soil. They grow wilted without water, and a prolonged absence of water causes death. As water outflow increases, their cells become flaccid at first, then plasmolyzed. This is what occurs when plants are overly exposed to sunshine or are drought-stricken. Desiccation of plants can also be induced, for example, when the plant is to be conserved and stored as a specimen.
Desiccation in Medicine
The term “dessicated” in medicine refers to something that has been kept dry. Pharmaceutical medicines and supplements are produced in a dry environment. Because moisture may degrade medical items, dessicated medicinal products have a longer shelf life.
Desiccation Citations
- Soil desiccation cracking and its characterization in vegetated soil: A perspective review. Sci Total Environ . 2020 Aug 10;729:138760.
- Desiccation Tolerance as the Basis of Long-Term Seed Viability. Int J Mol Sci . 2020 Dec 24;22(1):101.
- Desiccation Tolerance: Avoiding Cellular Damage During Drying and Rehydration. Annu Rev Plant Biol . 2020 Apr 29;71:435-460.
Share
Similar Post:
-
Angiosperm: Description, Characteristics, and Examples
Continue ReadingAngiosperm Definition
Angiosperm can be defined as those whose fertilized eggs forms seed within the ovary.
What is Angiosperm?
The word Angiosperm originates from a Greek word where “angeion” means vessel and “sperma” means seed. Flower bearing plants are called as Angiosperms. Belonging to the plants group. Along with the flower, it also bears seeds. It is one of the vast group of plants, with 453 families and 260,000 species within. In the category of Angiosperms are 80% of green plants.
In angiosperms, female and male organs are both found. They are found in almost all location, excluding those with extreme climatic condition such as in the depth of the ocean, poles, mountain ranges and etc. while they are present in various climatic conditions, they may be immersed in soil, water or present on the surface or freely floating. They vary in size from very small in millimeters to 100 meters. Example are huge trees to tiny shrubs and intermediary plants. Orchidaceae is the abundant species of Angiosperms. Examples are grasses, pea and daisies. They have applications in various fields such as medicine, wood products, jewelry, industrial products and pharmaceutical products.
Angiosperm Anatomy and Morphology
They belong to the phylum Anthophyta of flowering plants and consist of stamens, carpels and pollens. In flowering plants, pollen grains are the sperms, producing stamens. Within the pollen grain lies the males game which will interact with the female gamete in the plant’s ovaries. Angiosperms can reproduce sexually as well as asexually. As the pollen grains are smaller than that of gymnosperms, thus, reaching the eggs of female quicker. Without fertilization as well angiosperms can undergo the process through pollens; where stamens has a vital role in the flowering plants life cycle of fertilization. Through cross-pollinations, insects get attracted towards the flowers, due to their colors as well as smell.
Behind the flower, are ovaries encapsulated in the carpels. To produce seeds, fruits and flowers, pollens are obtained by the ovaries which starts the process. Thus, the very first step involves seed development, followed by flowers and its pollination to produce fruit. Angiosperms have characteristics that resemble synapomorphies. Within the carpels are the ovules present which carries the pollination process. For the double fertilization to occur and for the endospore formation, it requires pollen sac and three stamens. Sieve tubes and companion cells are present in phloem tissues.
Angiosperm Flowers and Anatomy
For the reproduction to occur, pollination is quite important. The male sex organ are the stamens that produces pollen, which then get translocated to the pistil, which is the part of the female angiosperm.
Angiosperm Flowers Anatomy
Pollination occurs when the pollen from the male reaches the female part. There are two types of pollination; self-pollination and cross pollination. Pollination agents are insects, invertebrates, mammals and wind.
Structure of Angiosperms
The reproductive organ in Angiosperms are flowers and roots, stems and leaves are the asexually reproductive organs. Root system and shoot system are the angiosperm structures. Shoot system is the one present above the soil, whereas the root system is the one that is present in the soil. Root system comes under the root domain whereas the shoot lies under the shoot domain.
Root System
Roots are the most vital part of the plant; without them the plant is nothing. Absorption of minerals, water, nutrient from the soil is the function of the roots and transfer it to the tips. Primary and Tertiary root system are the types of root systems, where taproot is seen which grows towards the ground in length to form roots, which can further grow diagonally and horizontally is the primary root system and from taproots production of more roots is known as secondary roots. Primary roots have a very short life-span, and thus their position is occupied by supplementary system of roots. Depending on the function, primary and tertiary roots gets altered. Examples are beetroot and carrot.
Stem System
To make the plant stand, and on which the fruits and flowers come is the stem. From the roots the nutrients, water and other essential requirements moves to the stem and then to the leaves, fruits, plants and animals. Hypocotyl allows the continuous transfer of nutrients from roots to stem. From the stem, when the leaves are formed it is known as nodes and the distance between two nodes is known as internodes. The type of branching seen in angiosperms are axillary and dichotomous; in axillary there are two types of branching sympodial and monopodial.
Leaves System
From the stem emerges the leaves. For the formation of leaves, lamina is the main part which consist of petiole, stipule and blade. To the petiole the base of the leaf and the blade is linked and on both the sides is the stipule present. From the blade, photosynthesis occurs and thus is green and flattened in shape. However, some leaves shows the absence of petiole and stipules. The pattern on the stem can be opposite, whorled, alternate and paired.
Angiosperm Life Cycle and Reproduction
Double fertilization occurs in the angiosperms, where from the seeds the male and female gametophyte are produced. Sporophyte is the step in the life cycle, where the adult angiosperm is formed are heterosporous. The pollens will be generated from the microspores and the gametophyte are the pollen grains of the male. The female gametophytes which is the ovule will be formed from megaspores. Within the pollen lies two types of cell, one will form the pollen tube and the other will make up sperms.
The ovule is covered by another wall to keep the megasporangium intact, where meiosis takes place to produce a huge and three tiny megaspores, where only the huge megaspore reaches the embryo sac and gets three time divided after which the eight cell further moves. The four cells move towards the equator and the rest move to the pole resulting in the formation of 2n polar nucleus. There are helping cells present which are the synergids, nucleus, antipodal cell and an egg sac which is inside a mature embryo sac. As soon as the pollens reach the stigma, the sperms reaches the embryo sac and double fertilization starts, where the sperm and egg combines to form the embryo, whereas there is fusion of the polar nuclei and the second sperm going on. They form an endosperm, which stores the food.
On the basis of the leaves, angiosperms can be divided into eudicots and the monocots. On the embryo surface there are seed leaves which contain protein, lipid and sugars. There exist three species of angiosperm and they are where on the flower, stamen and pistil are present is the hermaphroditic. Monecious, where both the stamen and pistil are on the same plant but different flower. When both stamens and pistil are present on different plants and different flower it is called as dioecious.
Monocot
In 1703, they were first discovered by Ray. In the seed presence of a single cotyledon are called as monocots. These monocots phylogenetic studies have been done in 19th century. They consist of fibrous system of roots. The flowers in monocots consist of three parts and are called as Trimerous. Woody tissues are either absent or only present in few cases. A vital feature seen in monocots is the presence of a single layer of pollens, which is even seen today. Examples of monocots plant are orchid, lilies, grasses and others, whereas monocot crops are sugarcane, pineapple, corns and others.
Dicot
More than one cotyledon in the seed is the Dicot. The flower in dicot consist of four or either five parts. The network seen in leaf is of reticulate venation type. The vascular tissue present in the ring forms the dicot. They are capable of producing woody tissues. In dicots the pollen consist of three layers. They have taproot system. Dicot examples are sunflowers, beans and oak.
Angiosperm Examples
There are numerous examples of angiosperms, however the most common one are the flowering plants. The most studied example of angiosperm are fruit trees. The fruits are formed from various flowering plants. Grains and grasses are also included in angiosperms. Fruits such as apple, cherries and oranges. However, the insects, birds, wind and mammals are the agents of pollination. After the pollination process get completed and the carpel has opened up, flowers get converted to fruits and will also change colors.
As wheat, rice grow in grasses and they cannot attract pollinators thus, the agent for pollination to take place is wind as they carry the seed because its light in weight. Thus, angiosperms are very vitals as various crops are available to humans because of them.
History of Angiosperm
In the Mesozoic era, the fossil records have been first seen in history. They possess both male and female gametophytes and are the flowering plants. Around 100 million years ago, these plants were identified in the middle cretaceous and were viewed 125 million years prior by the paleontologist. Although there aren’t much traces of history of angiosperm but fossil of pollen has been obtained, and were believed to have quite similarity to angiosperms.
It is said that from the gymnosperms, angiosperm has been arrived, but yet studies are going on, as they form a different set of species on the basis of its features. They believed angiosperms to be originated from tropical grasses or woody bushes.
In the south pacific, there is a rain forest in New Caledonia which has a flowering plant which is quite small and is quite ancient it is the Amborellatrichopoda and is confirmed that is a flowering plant. The other angiosperms are the monocots and the eudicots. Basal angiosperms were also part of the angiosperm, but however have been removed from the category of angiosperm.
Angiosperm Fossil Record
The very first record of the angiosperm fossil is of 132 million years ago. There is quite a lot of differences seen in the size, structure, flowers in the ancient old angiosperms and those of the modern era. Although the only similarity found was in the flowers. Thus, classifying them into the category of Angiosperms.
Estimation of Age of the Angiosperms
This information of how old the angiosperms are since how long they have existed can be identified with the fossil. Modern and molecular techniques have been used to determine the origin of flowering plants and has said that they are 5-45 millions years old. Various researchers have worked on the finding of origination of angiosperm using various tools and techniques and have found that the age of angiosperm is 165-199 Ma and for other plants as well have been found.
Angiosperms Ecological Importance
They have a huge role in various fields, on the environment and on humans as well as animals. The flowering plants are quite important as they keep the food chain continuing. Many insects, birds and other mammals eat these plants. These plants are also source of pollination to other insects. They provide us fruits, flowers along with seed, as many animals can continue lifecycle when they consume the fruits and obtain energy.
The seed propagation takes place when birds and other mammals eat them and take the seeds to various locations, thus resulting in more flowering plants. They also produce various products such as alkaloid, oil and glycosides. They also prevent the predators from causing harm to the other plants and stop them from producing toxic compounds. It is said that thousands of birds, animals get their food the angiosperm tree, thus, they maintain the food chain and keep it running.
Economic Importance of Angiosperm
They have application in various industries which starts from the pharmaceutical industry. Majority of the antibiotics, drugs are either made from angiosperms or are the derivative of angiosperms. Narcotic, vitamins, aspirin and quinine are some of the example. These angiosperms have shown promising results in treating cardiac arrest and various forms of cancer.
For heart surgeries and for relaxation of muscle, curare is used. For treating malaria, quinine is used. For cancer, vincristine has been used and for oral contraceptives diosgenin has been used. They also play a role in preserving the environment. Humans and animals are dependent on angiosperms for food and their absence would have a major impact on the environment as well as on every individual.
Angiosperms vs Gymnosperms
Flowering plants are Angiosperms. Example are grains, fruits, vegetables and others. Gymnosperms are non-flowering plants and their examples are juniper, pine, cedar and fir. Accumulation of gymnosperms form, cones whereas the accumulation of angiosperm forms flowers. Angiosperms are mostly unisexual whereas the gymnosperms are bisexual. In angiosperms there are various flowering parts such as style, stigma, petals and sepals. Archegonia is found in gymnosperms and is absent in angiosperms. On the stalk are the angiosperms present. Angiosperms and gymnosperms also vary in the cotyledon number. Angiosperms have application in food, ornament, timber and pharmaceutical, whereas gymnosperms in making of ply, paper and lumber.
Angiosperm Citations
- Vessel-associated cells in angiosperm xylem: Highly specialized living cells at the symplast-apoplast boundary. Am J Bot . 2018 Feb;105(2):151-160.
- Angiosperm Plant Desiccation Tolerance: Hints from Transcriptomics and Genome Sequencing. Trends Plant Sci . 2017 Aug;22(8):705-717.
- Angiosperm ovules: diversity, development, evolution. Ann Bot . 2011 Jun;107(9):1465-89.
- Key questions and challenges in angiosperm macroevolution. New Phytol . 2018 Sep;219(4):1170-1187.
Share
Similar Post:
