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Mass Number: Definition, Calculation, and Examples
Continue ReadingWhat is Mass Number?
The sum of number of protons and neutrons is termed as the mass number of an atom.
It is represented by using the letter ‘A.’
The symbol A is derived from a German word Atomgewicht means atomic weight. Protons and neutrons present in the nucleus of an atom together, are also called nucleons.
For instance, an atom of Oxygen has 8 protons and 8 neutrons in the nucleus of its atom. Thus, its mass number is 8+8= 16.
The number of protons is the same in all atoms of an element that means, it is unique for all elements, the number of neutrons can vary. Therefore, atoms of the same element can have different mass numbers.
These types of structure are named as isotopes.
The weight of an electron in an atom is nearly insignificant. Therefore, the atomic mass of an atom is approximately the same as its mass number.
Mass Number vs Atomic Number
Atomic Number Mass Number The atomic number is defined as the total number of protons present in the nucleus of an atom. The total number of protons and neutrons present in the nucleus of an atom gives us the mass number of an atom. It is commonly signified with the letter ‘Z.’ It is commonly represented using the letter ‘A.’ All the atoms of a specific element have the same number of protons, and henceforth they have the same atomic number. Protons and neutrons present in the nucleus of an atom together, are called nucleons. For example, all carbon atoms have an atomic number equal to 6, however all atoms of Oxygen have 8 protons in their nucleus thus atomic number of oxygens is 8. For instance, an atom of carbon has 6 protons and 6 neutrons. Thus, the mass number of carbon atom is 12. If we want to find the valency of a substance, then we see the electrons present in the outermost shell of the atom. But to further find the atomic number or the mass number, we need to know the total number of protons and neutrons present in the nucleus of an atom.
Uses of Mass Number
The mass number of an element is convenient to determine the isotopic mass which is generally calculated in the atomic mass units or amu.
An isotope of an element is referred to the elements having same atomic number but different mass number. Isotope thus differs in the number of neutrons.
Usually, atomic mass and mass numbers are two different terms and can vary only by an insignificant value. In most of the cases, they are different. Though, as the weight of an electron is insignificant so it can be said that the atomic mass of an atom is almost equal to mass number.
There are some substances which are named as Isobars. These are defined as the atoms of different elements having the same mass number, but different atomic numbers.
For example, Chlorine-37 and Argon-37 have the same mass number. But their atomic numbers are 17 and 18 respectively. Hence, they are called isobars.
The heavier atoms frequently practice alpha decay where they terminate 2 protons and 2 neutrons from their radioactive nucleus respectively, the mass number of elements is then altered consequently.
In conclusion, the mass number is altered by total 4 units.
Notation of Atom
To write the notation of any atom, we need to know the symbol of the element, the atomic number, and also the mass number.
The mass number of the atom goes in superscript of the symbol and the atomic number is written below as a subscript as shown below.
For example: potassium (K) has an atomic number 19 and mass number is 39 is written as;
19K39
Mass Number Calculation
If the number of protons and the mass number of an element is given, then we can also find the number of neutrons simply by subtracting its atomic number from its mass number as shown below;
No of neutron = mass number – atomic number
Or
N = A – Z
Mass Number Calculation Example
An atom has an atomic number of 11 and a mass number of 23.
1. Find the number of protons
2. Determine the number of neutrons in the nucleus of an atom.
3. The number of electrons present in nucleus of atom
Solution:
1. As we know the atomic number is always equal to the number of protons present in the nucleus of an atom therefore,
Number of Protons = 11.
2. As we now know that the number of neutrons is always found by deducting the atomic number from the mass number as shown below;
N = A -Z
Therefore,
Number of neutrons = 23 – 11 =12 3.
As the number of protons is always equal to number of electrons present in a neutral atom.
So, Number of electrons = number of protons which is = 11
Mass Number Citations
- Dependence upon mass number and neutron excess of the real part of the proton optical potential for mass numbers 44 <= A <= 72. Phys Rev C Nucl Phys . 1986 Aug;34(2):468-479.
- Dependence of actinide production on the mass number of the projectile: Xe +248Cm. Phys Rev C Nucl Phys . 1987 Jan;35(1):204-212.
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Thomson Atomic model: Definition, Experiments, and Limitation
Continue ReadingWhat is Thomson Atomic Model?
Thomson atomic model was proposed by William Thomson in the year 1900. This model described the inner structure of the atom theoretically.
This theory was strongly supported by Sir Joseph Thomson, who had discovered the electron initially.
Thomson presumed that an electron is two thousand times lighter as compared to proton and thought that an atom is made up of thousands of electrons.
In this atomic structure model, he stated that the atoms are fenced by a cloud having positive as well as negative charges.
Thomson atomic model of an atom is reffered to as a plum pudding. However, at that time the atomic nucleus was yet to be discovered. So, Thomson projected a model on the basis of known properties of atom that was available at that time.
The known properties are mentioned below:
• Normally, atoms are neutrally charged particles.
• Negatively charged particles named as electrons are present in an atom.
Thomson Pudding Atomic Model
Thomson projected that the shape of an atom is similar to that of a sphere having a radius of 10-10 m.
The positively charged particles are uniformly scattered with electrons arranged in such a way that the atom is thus electrostatically stable.
Thomson atomic model was also named as the plum pudding model or the watermelon model.
The electrons present in an atom resembled the seeds that are embedded in a watermelon whereas the watermelon’s red mass signified the positive charge distribution in atom.
Postulates of Thomson Atomic Model
An atom generally contains a positively charged sphere with electrons that are embedded in it.
An atom as an entire particle is electrically neutral because the negative and positive charges present are equal in magnitude.
Thomson stated that the model of an atom is similar to the structure of watermelon.
Where he considered:
• Watermelon seeds are represented as negatively charged particles.
• The red part of the watermelon is represented as positively charged.
• According to the postulates of Thomson’s atomic model, an atom is similar to a sphere of positive charge with electrons or negatively charged particles that are present inside the sphere.
• The positive and negative charges present in atom is equal in magnitude.So, an atom has no charge and is considered to be electrically neutral.
• Thomson’s atomic model is similar to a structure of a spherical plum pudding and a watermelon.
Limitations of Thomson Atomic Model
• Thomson was unable to explain the stability of an atom because his model of atom failed to describe how a positive charge particles holds the negatively charged electrons in an atom. Consequently, Thomson’s theory also failed to justify the position of the nucleus in an atom.
• Thomson’s model was unable to explain the scattering of alpha particles by thin metal foils that was explained by Rutherford.
• Even though Thomson’s model was not a precise model to account for the atomic structure, it still proved to be the base for the expansion of other atomic models. The study of the atom and its structure has flagged a way for several inventions that have played an important role in the development of humankind.
Thomson Atomic model Conclusion
Even though Thomson’s atomic model was not precise and had a few drawbacks, it still provided the base for several other atomic structure models that were later discovered. It is thus one of the foundation models that led to important and revolutionary discoveries.
Thomson Atomic model Citations
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Rutherford Atomic Model: Definition, Experiments, and Limitation
Continue ReadingWhat is Rutherford Atomic Model?
In 1904, J.J. Thomson proposed the plum pudding model of an atom. He stated that an atom is a positive charge sphere in which electrons (negative charge) are embedded.
He also stated that the atom is electrically neutral as positive charge and negative charge present inside the nucleus of an atom are equal. But this model could not describe the stability of the atom.
Ernest Rutherford, a British scientist conducted an experiment named ‘alpha gold-foil, and thus based on those observations, he proposed the atomic structure of elements and which came to known as the Rutherford Atomic Model.
Rutherford Atomic Model and His Alpha Scattering Experiment
Rutherford performed an experiment by bombarding a thin sheet of gold with alpha particles and then studied the path of these particles after they contacted with the gold foil.
Rutherford, in his experiment, bombarded high-energy streams of α-particles from a source of radioactive element of a thin sheet (100 nm thickness) of gold.
He placed a fluorescent zinc sulfide screen around the thin gold foil to study the variation in path of alpha particles.
Rutherford’s observations thus opposed Thomson’s atomic model. Reason for using gold foil in the experiment Gold is the most malleable metal of all metals.
Thus, It can easily be converted into very thin sheets. Reason for choosing alpha particles in the experiment Alpha particles are referred to as double-charged Helium atoms, and they have more momentum. Furthermore, they deviate least from their path.
Alpha Scattering Experiment's Observation
The observations made by Rutherford are mentioned below:
1. A greater fraction of the α-particles that were bombarded on the gold sheet passed through it without any deflection, and hence that means that most of the space in an atom is empty.
2. Some of the α-particles were deflected by the gold sheet at minor angles, and it was found that the positive charge in the atom is not distributed uniformly.
3. Very few of the α-particles were commonly deflected back, that is only a few α-particles one in every 12000 alpha particles bombarded were deflected at an angle 180o. So, the volume occupied by the positively charged particles in an atom inhabits a small volume as compared to the total volume of an atom.
Rutherford Atomic Model
Based on the above finding and conclusions, Rutherford further proposed the atomic structure of elements. Hence, the Rutherford’s atomic model proposed that:
1. The positively charged particles and most of the mass of an atom was concentrated in a very small volume inside an atom. This small positively charged body present in the atom is named as nucleus.
2. He also proposed that the negatively charged electrons surround the nucleus present in an atom. He demonstrated that the electrons that surrounds the nucleus revolve around it at a very high speed in circular paths. These circular paths are termed as orbits.
3. He stated that the electrons having negatively charged and the nucleus having the positively charged constituents are generally held together by a strong electrostatic force of attraction.
Rutherford Atomic Model and Modern Science
Rutherford’s finding helped the scientists to realise that the atom is not just made up of a single particle, but instead it consists of smaller subatomic particles.
Rutherford’s gold foil experiment also helped the scientists to find the exact atomic structure of an atom. Scientists eventually discovered that atoms have a positively charged nucleus present in the centre and radius of atom found to be 1.2 × 10−15 meters × [atomic mass number]1⁄3.
Subsequently, scientists found the number of electrons present in an atom by using X-rays. When an X-ray is passed through an atom, some part of it usually scatter, while the remaining rays pass through the atom.
As the X-ray commonly loses its intensity when electrons are scattered, then the number of electrons contained in an atom can be accurately estimated thus by finding the rate of decrease.
Limitation of Rutherford Atomic Model
The Rutherford atomic model was based on experimental observations, yet it failed to explain few things as mentioned below;
• Rutherford’s model was unable to explain the stability of an atom.
• Rutherford model did not discuss anything about the arrangement of an electron in orbit as well.
• According to Rutherford’s atomic model, electrons revolve around the nucleus in a circular path called orbits. But particles that are in motion around the nucleus on a circular path would experience acceleration, and this acceleration causes radiation of energy by charged particles. Ultimately, the electrons should lose energy and fall into the nucleus of an atom.
• Other drawback of the Rutherford model was a that he was unable to explain anything about the distribution of electrons in an atom.
• Definite lines in the hydrogen spectrum could also not be clarified by this model of atom.
Rutherford Atomic Model Citations
- Simulation of Rutherford backscattering spectrometry from arbitrary atom structures. Phys Rev E . 2016 Oct;94(4-1):043319.
- Comparison of Rutherford’s atomic model with the Standard Model of particle physics and other models.
- Rutherford’s Contribution. Science 25 Apr 1997: Vol. 276, Issue 5312, pp. 513-517
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Molarity: Definition, Calculation, Equation, and Formula
Continue ReadingWhat is Molarity?
The molarity (M) of a solution is defined as the number of moles of solute dissolved in one liter of solution.
To analyze the molarity of a solution, divide the moles of solute present in a solution by the volume of the solution stated in liters.
Molarity Equation
Equation used for finding the molarity of a solution is given below;
Molarity (M) = moles of solute / liters of solution = mol/L
When a molarity is reported, the unit used to represent is M and it is generally read as “molar”.
For instance, a solution labeled as 1.9 M NH 3 is read as “1.9 molar ammonia solution”.
One molar is referred to as the molarity of a solution where one gram of solute is dissolved in one liter of solution.
Molarity vs Molality
1) Molarity is referred to as concentration of a substance that is calculated as the number of moles of solute that is dissolved in one liter of solution while molality is defined as concentration of a substance that is calculated as the number of moles of solute found in one kg of solvent.
2) The molarity is represented by the symbol M, whereas molality is represented by a symbol m .
3) The formula for molarity is written as moles / liter whereas the formula for molality is written as moles / kg.
4) Molarity is generally affected by changes in temperature of the system while molality is not affected by changes in temperature of system.
5) Molarity is usually affected by changes in pressure whereas molality is not affected by changes in pressure of system.
6) Molarity may result in a vague and inexact concentration, whereas molality always results in an accurate and exact measurement of concentration of solution.
How to Calculate Molarity #1
A solution is prepared by dissolving 52.23 g of NH 4 Cl into enough water to make 600.0 mL of solution. Calculate its molarity.
Given; Mass – 52.23 g NH4Cl
Molar mass of NH4Cl = 53.50 g/mol
Volume of solution given = 600.0 mL = 0.600 L
Initially, the mass of the ammonium chloride given is converted to moles. Then the molarity is calculated of the solution by dividing by liters.
52.23 g NH4Cl x (1mol of NH 4 Cl / 53.50 g NH 4 Cl) = 0.9762 g
The given volume has to be converted to liters.
0.9762 / 0.600 = 1.621 M
The molarity is 1.621 M, this means that a litre of the solution would contain 1.621 mol NH4Cl.
How to Calculate Molarity #2
A chemist needs to make 4.00 L of a 0.350 M solution of potassium permanganate (KMnO4). What mass of KMnO4 does she need to make the above solution?
Given; molarity = 0.350 M
volume = 4.00 L
molar mass KMnO4 = 158.04 g/mol
Unknown ; mass KMnO4 = ? g
Moles of solute can be calculated by multiplying molarity of solution by liters. Then, moles has to be converted to grams.
Mol KMnO4 = 0.350 M KMnO4 x 4.00 liter = 1.4 mol KMnO4
1.4 mol KMnO4 x (158.04 g/mol/ 1 mol KMnO4) = 221.5 g KMnO4
When 221.5 g of potassium permanganate is dissolved into water to make 4.00 L of solution, and the molarity is 0.350 M.
Molarity Citations
- Relationship between Molarity and Color in the Crystal (‘Dramada’) Produced by Scytalidium cuboideum, in Two Solvents. Molecules . 2018 Oct 9;23(10):2581.
- The Relationship between Effective Molarity and Affinity Governs Rate Enhancements in Tethered Kinase-Substrate Reactions. Biochemistry . 2020 Jun 16;59(23):2182-2193.
- Effective molarity redux: Proximity as a guiding force in chemistry and biology. Isr J Chem . 2013 Aug;53(8):567-576.
- The effect of buffer molarity on the size, shape and sheath thickness of peripheral myelinated nerve fibres. J Anat . 1982 Aug;135(Pt 1):183-90.
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Mole Fraction: Definition, Calculation, and Formula
Continue ReadingWhat is Mole Fraction?
The mole fraction is defined as the ratio of number of moles of a given component present in a solution to total number of moles present in the given solution.
Mole fraction is one of the ways to find the concentration of the given solution.
A unit of concentration is termed as a mole fraction.
The mole fraction thus calculates the relative amount of solute and solvents present in each solution.
Mole fraction are unitless quantity, have no dimensions, and the sum of all fraction in a mixture is always equal to 1.
Mole fraction is represented by a symbol X.
Mole Fraction Formula
if a mixture is composed of two substance that are A and B, then the mole fraction is calculated as given below:
XA = mol A / (mol A + mol B) and XB =mol B / (mol A + mol B)
Mole Fraction of Solute = Moles of solute / (Mole of Solute + Mole of Solvent)
For instance, if a mixture contains 0.80 mol A and 1.0 mol B
mole fraction of A =0.8/1.5 =0.44
mole fraction of B = 1.0/1.8 = 0.55
The Mole fraction can also be converted into mole percentage by multiplying it by 100.
Properties of the Mole Fraction
The mole fraction is used broadly in the construction of phase diagrams. It has a lot of advantages which are mentioned below:
Mole fraction does not generally depend on temperature as compared to molar concentration, and it does not need knowledge of the densities of the involved phases.
It is very easy to make a mixture of known mole fractions by weighing the appropriate masses of the constituents used to form a mixture.
A mole fraction of a substance is referred to as the function of other component present in a tertiary mixture.
Disadvantages of Mole Fraction
The one disadvantage of mole fraction is that mole fraction is not suitable for liquid solutions.
How to Find Mole Fraction in Mixtures?
A mixture of gases is made by combining 6.8 moles of O2 and 4.6 moles of N2, find the mole fraction of nitrogen in this mixture?
Total number of moles = 6.8 +4.6 = 11.4
moles of N2 = 5.6 /11.9
= 0.403
So, mole fraction of N2 = 0.403
How to Find Mole Fraction in Solution?
Find the mole fraction of NaCl if 0.200 moles of sodium chloride are dissolved in water.
Primarily, convert volume of water into mass and then to moles
Density is defined as mass divided by its volume.
Density = Mass / Volume
M = D*V = 1g/ml * 100 ml =100 g
So, Moles of water = Mass / total molar mass
= 100 / 18 = 5.55 moles
Total number of moles = 5.55 + 0.200 = 5.75 moles
Thus, Mole fraction of NaCl = 0.200 / 5.75 = 0.0347
How to Find Mole Fraction Multi-Component Mixtures?
To find the mole fraction of Hexane in the mixture of 10.0 g of pentane(C5H12), 10.0 f of hexane (C6H14) and 10.0 g of benzene (C6H6).
Primarily, find the number of moles in 10.0 g of each component by the formula:
Number of moles = Given mass /Molar Mass
Number of moles of Pentane is equal to 0.138 moles
Moles of hexane is equal to 0.116 moles
Moles of benzene is equal to 0.128 moles
Hence, Total number of moles present = 0.138 + 0.116 + 0.128 = 0.382
Lastly, The mole fraction of hexane is = 0.116 / 0.382 = 0.303.
How to Find Mole Fraction from Molality?
If 1.82 m solution of table sugar (C6H12O6) is formed in water, find the mole fraction of the table sugar?
As the molality of a solution is given thus, we can convert it to the equivalent mole fraction, which is a mass ratio as given below;
Molality = moles solute / kg of solvent.
As per the definition of molality, we have 1.82 moles of sugar solution and 1.00 kg (1000 g) of water. We know the number of moles of sugar, thus we need to find the moles of water using its molecular weight as given below;
Moles of water = 1000 / 18 = 5.55 moles
Total number of moles is equal to 5.55 + 1.82 = 7.37 moles
Mole fraction of sugar = 1.82 / 7.37 = 0.246
How to Find Mole Fraction from Mass Percent?
Find the mole fraction of cinnamic acid with a mole percent of 60.00% urea in cinnamic acid. The molecular weight of urea is 60.16 g/mol and the molecular weight of cinnamic acid is 148.16 g/mol.
By assuming a total mass of 100.0 g which means that we have 60.0 g of urea and 40.0 g of cinnamic acid.
Thus, we can then find the moles present of Urea and Cinnamic acid by dividing each by its molecular weight as shown below;
Numbers of moles of Urea = 60.0 / 60.16 g/mol = 0.997 moles
Numbers of moles of cinnamic acid = 40.0/148.16g/mol = 0.269 moles
Total number of moles is equal to 1.266 moles
Mole fraction of cinnamic acid = 0.269/1.266 = 0.2124
Citations
- The reciprocal calculation procedure for setting occupational exposure limits for hydrocarbon solvents: An update. Journal of Occupational and Environmental Hygiene Volume 14, 2017 – Issue 8.
- Anomalous mole fraction effect, electrostatics, and binding in ionic channels. Biophys J . 1998 May;74(5):2327-34.
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Discovery of Protons: Model, Discovery, and Experiment
Continue ReadingWhat are Protons?
The three different sub-atomic particles present in the nuclei of an atom are called, protons, neutrons, and electrons and they were discovered in the nineteenth and twentieth century.
Discovery of Protons
The nucleus of the atom was discovered by a scientist named Ernest Rutherford in the year 1911 in his well-known gold foil experiment. He stated that all the positively charged particles present in an atom were concentrated in a singular core and that maximum of the atom’s volume was empty.
He also stated that the total number of positively charged particles present in the nucleus of an atom is always equal to the total number of negatively charged electrons present around it.
The finding of the proton is credited to Ernest Rutherford, who showed that the nucleus of the hydrogen atom (that is a proton) is present in the nuclei of all atoms in the year 1917. But, the presence of a positively charged particle found in an atom had been first noticed by E. Goldstein in the year 1886 based on the concept that atoms are generally electrically neutral which means that they have the same number of positive and negative charges.
He performed a series of experiments and detected that when high voltage electricity was passed through a cathode tube which was fitted with a perforated cathode (pierced disk) and thus contained gas at low pressure then a new type of ray was produced from a positive electrode or commonly called as the anode which moved towards the cathode.
These new rays he named as canal rays, positive rays, or anode rays. Further, the canal Ray experiment is the experiment that was performed by German scientist Eugen Goldsteinin that led to the discovery of the proton. The discovery of proton occurred after the discovery of the electron which further supported the structure of the atom.
The Canal Ray Experiment
• The apparatus as shown above in the figure is set by providing a very high voltage source and emptying the air to preserve low pressure inside the tube.
• High voltage is thus passed to the two metal pieces as shown to ionize the air and hence making it a conductor of electricity.
• The electricity started to flow as the circuit completes.
• When the voltage was increased further to several thousand volts, then a faint luminous ray was observed extending from the holes in the back of the cathode.
• The rays thus observed were moving in the opposite direction of cathode rays and were termed as canal rays.
Conclusion of Canal Ray Experiments
• As compared to cathode rays, canal rays depend upon the nature of gas present in that tube. It is because of the fact that the canal rays consisted of positive ionized ions which were formed by the ionization of gas present in the tube.
• The behavior of particles present in an electric and magnetic field was thus the opposite to that of cathode rays.
Protons Characteristic
Protons are referred to as the positively charged subatomic particles of an atom. It is represented by the symbol p or p+.
A hydrogen atom comprises of one proton and one electron, so when an electron is removed from the hydrogen atom then a proton is produced. This is the reason why the proton is also represented as H+.
It thus possesses +1e (or 1.60 10-19 coulomb) positive electric charge.
The word Proton is a Greek word that means ‘First’. It was initially used by Ernest Rutherford in the year 1920. The subatomic particles protons and neutrons are collectively known as nucleons.
What is The Mass of Protons?
The mass of the proton is 1.67 10-24 gram or 1.67 10-27 kg.
The mass of an electron is equal to 9.1 10-28 consequently the mass of a proton is 1836 times the mass of an electron. Though the mass of a proton is almost always equal to the mass of a neutron present in the nuclei of an atom.
The number of protons present inside the nucleus of an atom is always equal to the atomic number (Z) of the atom.
Mathematically,
Number of Protons = Atomic Number
For instance, the atomic number of the Krypton (Kr) atom is equal to 36. Henceforth, the nucleus of the Krypton atom consists of 36 protons.
Properties of Protons / Positive Rays / Anode Rays
1. They are positively charged ions.
2. They travel in straight lines and thus can cast a shadow of the thing located in their path.
3. These positive rays are also deflected by electric as well as a magnetic field.
4. Mass of proton is equal to 1.672 x 10-24 g.
5. The charge on the proton is equal to +1.602 x 10-19 coulombs.
Protons Citations
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Discovery of Neutrons: Model, Discovery, and Experiment
Continue ReadingWhat are Neutrons?
Neutrons are referred to as subatomic particles that are one of the main constituents of atomic nuclei.
Neutrons are generally denoted by the symbol n or no.
Neutrons do not have any net electric charge linked to them. They do, though, have a mass that is slightly greater in magnitude as compared to a proton.
Neutrons and protons are together referred to as nucleons since they usually behave similarly.
The mass of a neutron can be nearly approximated to one atomic mass unit or amu.
Nuclear physics is the branch of science that deals with the study of the properties of neutrons and the relations of these subatomic particles with other substances.
The complete nuclear and chemical properties of an element are generally determined by the total number of protons present in its atomic nucleus (atomic number) and the total number of neutrons present in its respective atomic nucleus or it is also referred to as the neutron number.
The sum of the total number of protons present in a nucleus of a given atom and the total number of neutrons in the atomic nucleus gives the mass number of that atomic nucleus.
The protons and the neutrons present inside the nucleus of an atom are bound together through nuclear forces.
For the stability of atomic nuclei, the existence of neutrons is essential. The only exception to the above-mentioned rule is the nucleus of protium or hydrogen-1.
Discovery of Neutrons
Neutrons were initially hypothesized by the New Zealand-born British physicist named Ernest Rutherford in the year 1920.
But, the discovery of neutrons is credited to the British physicist named James Chadwick in the year 1932. He was also awarded the Nobel prize in physics for this finding in the year 1935.
During the year the 1920s, the common hypothesis on the nature of atoms was that they comprised of protons and also nuclear particles called electrons. Though, this failed to obey the Heisenberg uncertainty principle in quantum mechanics.
Consequently, in the year 1931, two German nuclear physicists noticed that when the alpha particle radiation that is emitted by polonium is made incident on beryllium, lithium, or boron, it then resulted in the production of a strangely penetrating form of radiation.
Further, it was confirmed by James Chadwick through a series of trials that these particles that constituted the strangely penetrating radiation were called neutrons.
James Chadwick fired alpha radiation at the beryllium sheet from a polonium source which led to the creation of uncharged, penetrating radiation.
This uncharged, penetrating radiation was thus made incident on paraffin wax, a hydrocarbon having a fairly high hydrogen content.
The protons that were ejected from the paraffin wax were noticed with the help of an ionization chamber.
This range of the liberated protons was measured and the contact between this uncharged radiation and the atoms of numerous gases was studied by James Chadwick.
He, at last, concluded that the oddly penetrating radiation thus comprised of uncharged particles having (roughly) the same mass as that of a proton.
These particles were later called ‘neutrons’. The total number of protons and neutrons present in the nucleus of an atom indicates the mass number of that particular atom.
Mathematically,
Mass Number = (Number of Protons) + (Number of Neutrons)
Charge and Mass of Neutrons
The electric charge thus associated with a neutron is equal to 0. Hence, neutrons are neutrally charged subatomic particles.
The mass of a neutron is nearly equal to 1.008 atomic mass units.
Subsequently, the subatomic particles named as neutrons lack an electric charge, so their mass cannot be directly determined through the analytical technique of mass spectrometry.
Properties of Neutrons
Even though the neutron is considered to be a neutral particle, the magnetic moment of these particles (neutrons) is not equal to zero.
Even though electric fields have majorly no effect on neutrons, these subatomic particles are still affected by the presence of magnetic fields.
The magnetic moment related to the neutron can be considered as a sign of its quark organization or structure and the distribution of its internal charges.
The mass of neutrons is always equal to that of protons present inside the nucleus of an atom (Mass of the neutron is 1.675 x 10-24g).
The density of neutron is equal to 1.5 x 1014 g/cc.
Applications of Neutrons
In various nuclear reactions, the subatomic particle named as the neutron plays an important role.
Information about neutrons and their activity has been especially vital in the past for the expansion of many nuclear reactors and numerous nuclear weapons.
The nuclear fissioning of some elements such as uranium-235 and plutonium-239 is almost always triggered by their neutron absorption.
Warm, cold, and hot neutron radiation plays a very significant application in neutron scattering facilities where the radiation is often used in condensed matter research with the support of X-rays.
One of the most important applications of neutrons includes the excitation of delayed and triggered gamma rays from material components. This also forms the basis for the study of neutron activation analysis, frequently abbreviated to NAA.
NAA is most commonly used to examine the small samples of materials present inside a nuclear reactor.
Neutrons Citations
- Neutrons from high-energy x-ray medical accelerators: an estimate of risk to the radiotherapy patient. Med Phys . May-Jun 1984;11(3):231-41.
- Neutrons in active proton therapy: Parameterization of dose and dose equivalent. Z Med Phys . 2017 Jun;27(2):113-123.
- The potential and limitations of neutrons, electrons and X-rays for atomic resolution microscopy of unstained biological molecules. Q Rev Biophys . 1995 May;28(2):171-93.
- Neutrons are forever! Historical perspectives. Int J Radiat Biol . 2019 Jul;95(7):957-984.
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Bohr Model of Atom: Definition, Diagram, Example
Continue ReadingWhat is Bohr Model?
o The Bohr model was an improved form of earlier cubic model (1902), the plum-pudding model (1904), the Saturnian model (1904), and the Rutherford model.
o The Bohr model is sometimes also referred to as the Rutherford-Bohr model.
o Bohr combined Planck’s and Einstein’s quantization ideas into a model of the hydrogen atom that set the contradiction of atom stability and discrete spectra.
o The Bohr model of the hydrogen atom elucidates the connection between the quantization of photons and the quantized emission from the atoms.
o Bohr described the hydrogen atom in terms of an electron that moves in a circular orbit around a nucleus.
o He hypothesized that the electron was thus limited to certain orbits termed as discrete energy levels.
o Electrons can also jump between these orbits either by absorbing or releasing photons.
o When an electron travels from a higher-energy orbit to a more stable orbit, energy is emitted in the form of a photon. And when an electron jumps from a stable orbit to a more excited orbit, a photon of energy is absorbed.
o Hence, by using the Bohr model, we can analyse the energy of an electron and the radius of its orbit in any one-electron system.
Characteristic of Bohr Model
o The Bohr model represents that the electrons present in any atom revolve in orbits of different energy around the nucleus just like planet revolve around the sun.
o The term energy levels (or shells) are used to define these orbits of differing energy. He stated that the energy of an electron is quantized, which means electrons can move from one energy level to another but there is nothing in between.
o The energy level that is occupied by an electron is called its ground state. But by absorbing energy it can thus move to a higher-energy, less-stable level, or shell. This higher-energy, or less-stable state is termed as excited state of the electron.
o The electron can also return to its original, stable ground state by releasing the energy it has absorbed, as shown in the figure below.
Bohr Model of Atom
Ground and Excited States of Electron
o Bohr stated that an electron needs less energy if it close to the nucleus, but as it moves away from nucleus it needs more amount of energy.
o The frequency of the photon of light thus emitted depends upon the variance of two energy levels.
E2-E1 = hv
Where E2 is defined as the energy of higher level and E1 is defined as the energy of lower level and h is termed as Planck’s Constant.
o So, Bohr numbered the different energy levels or shells. These are numbered as 1,2,3,4…or K, L, M, N…. shells preliminary from the shell near to nucleus.
o Bohr also found that the numerous energy levels can occupy only a fixed number of electrons for instance; energy level 1 or K shell can accommodate only 2 electrons, energy level 2 or L shell has 8 electrons, and so on.
o Number in various shell is determined by the formula – 2n2 where n is defined as number of shells assigned to various energy shell of an atom.
Bohr Model of Atom
Merits of Bohr model
o The Bohr model was the foremost model to postulate the quantization of electron orbits in atoms. Thus, it indicates an early quantum theory that also gave a way to development of modern quantum theory. It presented the concept of a quantum number to define the atomic states of any atom.
o Bohr described the stability of atoms. He stated that an electron does not radiate energy if it is present in the same shell.
o He explained the spectrum of hydrogen and he also calculated the size of atom was accurately. The drawback of Rutherford model of atom was that the atoms become unstable when accelerated charge, radiated energy, and lastly fell into nucleus. This theory of Rutherford was thus eliminated.
Limitations of Bohr Model
o The Bohr atomic model theory explains that electrons of any atom have both a known radius and an orbit that is, fixed position and momentum at the same time, which is nearly impossible according to Heisenberg Uncertainty Principle.
o The Bohr atomic model theory properly explained the structure of small sized atoms for instance – hydrogen, but for larger atoms poor spectral predictions are obtained. Hence, it could not explain the structure of large sized atoms.
o The Zeeman effect could not be explained by Bohr which states that the spectral line generally splits into several components in the presence of a magnetic field.
o The Stark effect could not be explained by Bohr, which states that the spectral line generally splits into fine lines in the presence of an electric field.
o Bohr model cannot predict the relative intensities of several spectral lines.
Bohr Model Citations
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What are Isobars? Definition, Types, and Examples
Continue ReadingWhat are Isobars?
o Isobar is defined as the element which varies in their chemical property but has the same physical property.
o Consequently, it can be said that isobars are those elements which have a different atomic number and same mass number or nucleon number.
o Their chemical property differs because of the difference in the number of electrons that are present in their respective nuclei.
o The sum of the number of protons and neutrons together form the atomic mass of an element.
Atomic Mass = Protons +Neutrons
Protons and neutrons are together known as nucleons. Hence, it can be said that the number of nucleons that are present in the nucleus of an atom is always equal to the atomic mass of that atom. Thus, it will have the same number of nucleons.
o Isobars always have different atomic structure because of the difference in their respective atomic numbers.
o The number of neutrons present in a nucleus of an atom makes up the difference in the number of nucleons. Thus, isobar always have different chemical properties.
Isobars Examples
o The isobars iron and nickel. Iron and nickel have different atomic number 26 and 28 respectively. However, they have same mass number that is 58.
o Another example of isobars include; argon and calcium with different atomic numbers 18 and 20, respectively. But they have the same atomic mass that is 40.
o Moreover, sometimes there are series of an element that has same atomic mass.
o For instance, Cobalt (Co), Nickel (Ni), Copper (Cu), and Iron (Fe) have same atomic mass 64 but the atomic number of each differs.
oSome more examples are;
o 18Ar40 19K40 20Ca40 have same mass number 40, but different atomic number.
o 32Ce76, 34Se76 have same mass number 76, but different atomic number.
o 11Na24 12Mg24 have same mass number 24, but different atomic number.
o 26Fe58, 27Ni58 have same mass number 58, but different atomic number.
o 27Co64 28Ni64 have same mass number 64, but different atomic number.
Isotopes
o Atoms are made up of electrons, protons, and neutrons.
o The nucleus of an atom is made up of protons and neutrons and the electrons revolve around the nucleus.
o Isotopes are referred to as the atoms in which the number of neutrons varies and the number of protons is the same.
o From the above definition, it can be concluded that isotopes are defined as those elements that have the same atomic number and different mass number.
o For instance – isotopes of hydrogen: There are three isotopes of hydrogen and these are named as protium, deuterium, and tritium. All three of them that are mentioned above have the same number of protons, but the numbers of neutrons vary. In protium the number of neutrons is equal to zero, in deuterium, number of neutrons is equal to it is one and lastly in tritium, the number of neutrons is two.
Isotopes vs Isobars
Isobars Isotopes Isobars are referred to the atoms of different chemical elements having same atomic mass. Isotopes are referred to as the atoms with the same number of protons but different numbers of neutrons. The atomic masses are equal. The atomic masses vary. The physical properties are similar. Physical properties are different. Atomic numbers of elements are different. Atomic numbers of elements are the same. For Instances: 11Na24 12Mg24 Have same mass number 24, but different atomic number. For Instance:- Isotopes of Hydrogen- There are three isotopes of hydrogen and these are named as protium, deuterium, and tritium. Uses of Isobars
o Nuclear reactors may use the uranium’s isobars.
o Iodine’s Isobars are generally used in treatment of goitre.
o For cancer treatment, isobars of cobalt are usually used.
Isobars Citations
- Differentiation of hydroxyproline isomers and isobars in peptides by tandem mass spectrometry. Anal Chem . 1990 Aug 1;62(15):1691-5.
- Isobars, the coexistence curve, and the critical exponent β of N-isopropylacrylamide gels obtained using a simple experimental method. Phys Rev E Stat Nonlin Soft Matter Phys . 2013 Feb;87(2):022603.
- Unique Structural/Stereo-Isomer and Isobar Analysis of Novel Fentanyl Analogues in Postmortem and DUID Whole Blood by UHPLC-MS-MS. J Anal Toxicol . 2019 Oct 17;43(9):673-687.
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Cathode: Definition, Examples, and Anode vs Cathode
Continue ReadingWhat is Cathode?
o The terms Cathode and Anode were confirmed in 1834 by a scientist named William Whewell. He derived the words from the Greek word, kathodos which means ‘way down’ In simple words, an electrode is defined as a substance that helps in the conduction of electricity where the electric current either arrives or leaves the non-metallic medium like an electrolytic cell.
Electrode
o An electrode is referred to as the vital component of an electrochemical cell that makes contact with an electrolyte.
o Electrode usually acts as a metallic contact from which the current enters and leaves the electrolyte.
o More precisely, it can be said that the electrode provides a surface where a redox reaction generally takes place between the metal and the solution.
Types of Electrode
Electrodes comprise of;
i. Cathode
ii. Anode
Cathode Characteristic
o Cathode and anode are both defined by the flow of current. Consequently, a cathode is an electrode from which the current leaves a polarized electrical device.
o Similarly, an anode is an electrode from which a current generally enters into a polarized electrical device.
o Further, a cathode is also said to be either a hot cathode or a cold cathode.
o A cathode is heated in the presence of a filament to produce electrons by thermionic emission is commonly known as a hot cathode however cold cathodes are not heated by any filament.
o A cathode is generally labeled as cold if it emits more electrons than the ones produced by thermionic emission alone.
o In the most simple terms, an anode in electrochemistry is referred to the point where an oxidation reaction occurs.
o Commonly, at an anode, negative ions or anions because of their electrical potential tend to react or give off electrons.
Flow of Current
o In simple words, the current is referred to any movement of electrical charge.
o Current generally flows in the same direction as it flows in positive charge carriers.
o The cathode is the negatively charged electrode.
o Few points of the cathode are mentioned below;
o The cathode always attracts cations or positive charges.
o The cathode is the source of electrons or also called an electron accepter and can cause reduction to occur. It may take a positive charge.
o Because the cathode producess electrons, which naturally are the electrical species, it can also be said that cathodes produce charge or that the current flows from the cathode to the anode.
Anode vs Cathode
Some important differences between cathode and anode are mentioned below;
Anode Cathode The anode is defined as the electrode where electricity moves into. The cathode is defined as the electrode where electricity is given out or flows out of. The anode is generally the positive side. A cathode is always the negative side. It acts as an electron donor. It acts as an electron acceptor. In an electrolytic cell, an oxidation reaction usually takes place at the anode. In an electrolytic cell, a reduction reaction usually takes place at the cathode. In galvanic cells, an anode can also become a cathode. In galvanic cells, a cathode can also become an anode Cathode Citations
- Effect of anode-cathode configuration on paresthesia coverage in spinal cord stimulation. Neurosurgery . 1997 Sep;41(3):654-9; discussion 659-60.
- Anode and cathode materials characterization for a microbial fuel cell in half cell configuration. Water Sci Technol . 2011;63(10):2457-61.
- Investigations on the Fundamental Process of Cathode Electrolyte Interphase Formation and Evolution of High-Voltage Cathodes. ACS Appl Mater Interfaces . 2020 Jan 15;12(2):2319-2326.
- Revealing the role of the cathode-electrolyte interface on solid-state batteries. Nat Mater . 2021 May 20.
- Cathode performance as a factor in electricity generation in microbial fuel cells. Environ Sci Technol . 2004 Sep 15;38(18):4900-4.
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