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    Slater proposed some set of empirical rules to calculate the screening constant (σ) of various electrons present in different orbitals of an atom or an ion. Once we get the value of screening constant it is easy enough to find the effective nuclear charge (Z*).

Screening Effect:

    The Valence electron in a multi - electron atom is attracted by the nucleus and repelled by the electrons of inner-shells.
Slater's rule practice problems
Screening Effect
    The combined effect of this attractive and repulsive force acting on the valence electron is that the Valence - electron experiences less attraction from the nucleus. This is known as the screening effect.

Slater's Rules to Calculate the Screening Constant (σ):

Rules for an electron in the nS, nP level:
  1. The first to do is to write out the Electronic Configuration of Elements of the atom or the ion in the following order and grouping.
  2. (1S) (2S, 2P) (3S, 3P) (3d) (4S, 4P) (4d) (4f) (5S, 5P) etc.
    It may be noted that so far as the screening effect is concerned the S and P electrons belonging to the same principal quantum shell have the same effect as advocated by Slater.
    Na atom:
    (1S)2(2S, 2P)8(3S)1
  3. An electron in a certain (nS, nP) level is screened only by electrons in the same level and by the electrons of lower energy level.Electrons lying above (nS, nP) level do not screen any (nS, nP) electron to any extent. Higher energy electrons have no screening effect on any lower energy electrons. Estimation of screening constant of the valence electron of the Sodium atom, (1S)2 (2S, 2P)8 (3S)1(The Valence electron will be excluded from our Calculation). Estimation of screening constant of the 2P electron of the Sodium atom, one 2P electron and 3S electrons will be excluded from our Calculation.
  4. Electrons of an (nS, nP) level shield a valence electrons in the same group by 0.35 each. This is also true for the electrons of the nd or nf that is for the electrons in the same group.
  5. Electrons belonging to one lower quantum shell, that is (n-1) shell shield the valence electrons by 0.85 each.
  6. Electrons belonging to (n-2) or still lower quantum shell shield the valence electron by 1.0 each. This means the screening effect is complete.
(a) For valence electron of Na atom:
Screening Constant (σ),
= (2 × 1) + (8 × 0.85) + (0 × 0.35) = 8.8Effective Nuclear Charge(Z),
= (11 - 8.8)

= 2.2
(b) For Na+ ion:
Electronic configuration of Na+ ion,
(1S)2(2S, 2P)8
Screening Constant (σ),
= (2 × 1) + (8 × 0.85) + (0 × 0.35)
= 8.8
Effective Nuclear Charge(Z),
= (11 - 8.8)
= 2.2
(c) For 2P electron of Na atom:
Screening Constant (σ),
= (2 × 0.85) + (7 × 0.35)
= 4.15
  • Evaluate the Z of Magnesium ion:
    Mg+2 : (1S)2(2S, 2P)8
    σ = (2 × 0.85) + (8 × 0.35)
    = 4.5
    Z = (12 - 4.5)
    = 7.5
  • Find out effective atomic number of Potassium ion:
    K+ : (1S)2 (2S, 2P)8 (3S, 3P)8
    σ = (2 × 1.0) + (8 × 0.85) + (8×0.35)
    = 11.6
    Z = (19 - 11.6)
    = 7.4
  • Estimate the σ and Z of the valence electron of the fluorine atom:
    F atom : (1S)2 (2S, 2P)7
    The valence electron has to be left out of our estimation.
    σ= (2×0.85)+(6×0.35)
    = 3.8
    Z= (9 - 3.8)
    = 5.2
  • Evaluate the Z of Fluoride ion:
    F - ion : (1S)2 (2S, 2P)8
    σ = (2×0.85)+(8×0.35)
    = 4.5
    Z⋆= (9 - 4.5)
    = 4.5

Rules for an electron in the nd, nf level:

    The above rules are quite well for estimating the screening constant of S and P orbitals. However when a d or f electron being shielded the (iv) and (v) rule replaced by a new rules for estimation of screening constant.
    The replaced rules are:
    All electrons below the nd or nf level contribute 1.0 each towards the screening constant.
  1. Estimate the screening constant for the outermost 4S electron of Vanadium:
    • Vanadium has atomic number 23 and the electronic configuration according to the Slater's Rule is:
      (1S)2 (2S, 2P)8 (3S, 3P)8 (3d)3 (4S)2
      We have consider only one electron of the two 4S electrons.
      Screening Constant (σ)
      = (2 ×1.0) + (8×1.0) + (8×0.85) + (3×0.85) + (1×0.35)
      = 19.7
  2. Screening Constant for a 3d electron of Vanadium:
      Electronic Configuration according to Slater's Rule is:
      (1S)2 (2S, 2P)8 (3S, 3P)8 (3d)3 (4S)2
      We have consider only two electron of the three 3d electrons.
      Screening Constant (σ)
      = (2 ×1.0) + (8×1.0) + (8×1.0) + (2 ×0.35)
      = 18.70
  3. Evaluate the effective nuclear charge of Vanadium(II) Ion:
      Vanadium(II) :
      (1S)2 (2S, 2P)8(3S, 3P)8(3d)3
      Screening Constant (σ):
      = (2 ×1.0) + (8×1.0+(8×1.0) + (3×0.35)= 18.70
      Z= (23 - 19.70)
      = 3.95
    In the first transition series electron filling up process begins in the 3d level below a filled 4S2 level. During ionisation process will a 4S electron or a 3d electron be lost first? Explain with reference to chromium.
    Chromium has atomic number 24 and the electronic configuration according to the Slater's Rule is:
    (1S)2 (2S, 2P)8 (3S, 3P)8 (3d)5 (4S)1
    ∴ Screening Constant (σ) for the 4S electron is:
    σ = (2×1.0) + (8×1.0) + (8×1.0) + (3×0.85) + (0×0.35)
    = 21.05
    Effective nuclear charge,
    Z = (24 - 21.05)
    = 2.95
    And the Screening Constant (σ) for the 3d electron is:
    σ = (2×1.0) + (8×1.0) + (8×1.0) + (4×0.35)
    = 19.4
    Effective nuclear charge,
    Z = (24 - 19.40)= 4.60
    Hence 3d electron is more tightly held than a 4S electron. So during ionisation the 4S electron will be lost.
    Calculate the effective nuclear charge of the hydrogen atom.
    Hydrogen atom has a single 1S valence electron. There is no other electron to screen it from the nuclear charge of single proton.
    Thus, σ= 0 and Z = 1.0 - 0 = 1.0
    Thus hydrogen electron sees the full nuclear charge of the nucleus, that is the electron is totally exposed to the proton.
    Comment on the variation in effective nuclear charge for a 2P electron from carbon to oxygen.
    Electronic distribution according to the Slater's Rule is:
C (1S)2 (2S, 2P)4
N (1S)2 (2S, 2P)5
O (1S)2 (2S, 2P)6
    In carbon, 2P electron is screened by 1S2 2S2 2P1 electrons while in Nitrogen and Oxygen this is done by 1S2 2S2 2P2 and 1S2 2S2 2P3 electrons respectively.
    Thus Z for Nitrogen = Z for carbon + (1 nuclear charge) - Screening due to one 2P electron.
    = Z for Carbon + 1 - 0.35
    = Z for Carbon + 0.65
    and Z for Oxygen
    = Z for Nitrogen + 0.65
Thus effective nuclear charge will go up by the same amount from carbon to Nitrogen and then to Oxygen.

According to Lewis Concept an Acid-Base reaction involves an interaction of a vacant orbital of an acid (A) and a filled or unshared orbital of a base (B).
A + :B A : B 
Lewis Acid

Lewis Base

Adduct or Complex
The species A is called Lewis Acid or a generalized acid and B is called Lewis Base or a generalized base. A strong acid A and a strong base B, will form the stable complex A : B.
A concept known as Principle of Soft and Hard Acids and Bases(SHAB) Principle is very helpful in making a stability of the complex A : B.
According to this principle the complex A : B is most stable when A and B are either both soft or both hard.
The complex is least stable when one of the reactants (namely A and B) is very hard and the other one is very soft. 
In order to arrive at a comparative estimate of the donor properties of different bases, the preferences of a particular base to bind a proton H+ and methyl mercury (II) ion, [CH3HgB]+ was determined. Both the proton and methyl mercury cation can accommodate only one coordinate bond but the two cation vary widely in their preferences to bases. This preferences was estimated from the experimental determination of equilibrium constants for the exchange reactions:
BH+ + [CH3Hg(H2O)]+ [CH3HgB]+  + H3O+
The results indicate that bases in which the donor atom is N, O or F prefer to coordinate to the proton. Bases in which the donor atoms is P, S, I, Br, Cl or C prefer to coordinate to mercury.

Hard and Soft Bases:

The donor atoms in the first group have high Electronegativity, low Polaris ability and hard to oxidize. Such donors have been named ‘hard bases by Pearson, since they hold on to their electrons strongly. 
The donor atoms of second category are of low electronegativity, high polarisability, and are easy to oxidize. Such donors have been called ‘soft’ bases since they are hold on to their valence electrons rather loosely.
In simple terms hardness is associated with a tightly held electron shell with little tendency to polarise. On the other hand softness is associated with a loosely bound polarisable electron shell.
It will be seen that within a group of the periodic table softness of the Lewis bases increases with the increase in size of the donor atoms. 
Thus, among the halide ions softness increases in the order:
-Cl -Br -I -
Thus F - is the hardest and I - is the Softest base.
Definition of hard acid and soft acids and bases
Classification of Bases

Hard and Soft Acids:

After having gone through a classification of bases, a classification of Lewis acids is necessary. The preferences of a given Lewis acid towards ligands of different donor atoms is usually determined from the stability constant values of the respective complexes or from some other useful equilibrium constant measurements. When this is done, metal complexes with different donor atoms can be classified into two sets based on the sequences of their stabilities.
Hard acids have small acceptor atoms, are of high positive charge and do not contain unshared pair of electrons in their valence shell, although all these properties may not appear in one and the same acid. These properties lead to high electronegativity and low polarisability. In keeping with the naming of the bases, such acids are termed as 'Hard'Acids.
Hard Acids:

Soft acids have large acceptor atoms, are of low positive charge and contain ushered pairs of electrons in their valence shell. These properties lead to high polarisability and low electronegativity. Again in keeping with the naming of the bases, such acids are termed 'Soft' Acids
Soft Acids:
Difference between hard acid and soft acid and bases
Classification of Lewis Acids as Hard, Intermediate and Soft Acids
Classify the following as Hard and Soft Acids and Bases. 
(i) H- (ii) Ni+4 (iii) I+ (iv) H+
  1. The hydride ion has a negative charge and is far too large in size compared to the hydrogen atom. Its electronegativity is quite low and it will be highly polarisable by virtue of its large size. Hence it is Soft Base.
  2. Quadrivalent nickel has quite a high positive charge. Compared to bivalent nickel its size will be much smaller. Its electronegativity will be very high and polarisability will be low. Hence it is Hard Acid.
  3. Mono-positive iodine has a low positive charge and has a large size. It has a low electronegativity and a high polarisability. Hence it is a Soft Acids.
  4. H+ has the smallest size with a high positive charge density. It has no unshared pair of electrons in its valence shell. All these will give a high electronegativity and very low polarisability. Hence H+ is a Hard Acid.
Soft and Hard Acids and Bases (SHAB) Principle:
This principle also means that if there is a choice of reaction between an Acid and two Bases and two Acids and a Base,
A Hard Acid will prefer to combine with a Hard Base and a Soft Acid will prefer to combine with Soft Base and thus a more stable product will be obtained.
Hard Acid - Hard Base may interact by strong ionic forces. Hard Acids have small acceptor atoms and positive charge while the Hard Bases have small donor atoms but often with negative charge. Hence a strong ionic interaction will lead to Hard Acid - Base combination.
On other hand a Soft Acid - Soft Base combination mainly a covalent interaction. Soft Acids have large acceptor atoms, are of low positive charge and contain ushered pair of electrons in their valence shell.

Application of Soft and Hard Acids and Bases (SHAB) Principle:

  1. [CoF6]-3 is more stable than [CoI6]-3
  2. It will be seen that Co+3 is a hard acid
    F- is a hard base and I- is a soft base
    Hence [CoF6]-3 (Hard Acid + Hard Base) is more stable than [CoI6]-3 (Hard Acid + Soft Base).
  3. The existence of certain metal ores can also be rationalised by applying SHAB principle. Thus hard acids such as Mg+2, Ca+2 and Al+3 occur in nature as MgCO3, CaCO3 and Al2O3 and not as sulphides (MgS, CaS and Al2S3), since the anion CO3-2 and O-2 are hard bases and S-2 is a soft base.
  4. Soft acids such as Cu+, Ag+ and Hg+2 on the other hand occurs in nature as sulphides. The borderline acids such as Ni+2, Cu+2 and Pb+2 occur in nature both as carbonates and sulphides. 
    The combination of hard acids and hard bases occurs mainly through ionic bonding as in Mg(OH)2 and that of soft acids and soft bases occurs mainly by covalent bonding as in HgI2.
AgI2- is stable, but AgF2- does not exist. Explain.
We know that Ag+ is a soft acid, F- is hard base and I- is soft base.
Hence AgI2- (Soft Acid + Soft Base) is a stable complex and AgF2- (Soft Acid + Hard Base) does not exist.
Explains why Hg(OH)₂ dissolved readily in acidic aqueous solution but HgS does not?
In the case of Hg(OH)2 and HgS, Hg is a soft acid and OH- and S-2 is hard base and soft base respectively. Evidently HgS (Soft acid + Soft base) will be more stable than Hg(OH)2 (Soft Acid + Hard base). More stability of HgS than that of Hg(OH)₂ explain why Hg(OH)2 dissolved readily in Acidic Aqueous Solution but HgS does not. 


An orbital is a region in space where there is a high probability of finding electron.

Orbitals and Quantum Number:

A wave function represents an electron is the product of two parts, a radial part and an angular part The square of the radial part of the wave function indicate the probability of finding the electron at any distance r from the nucleus.  The square of the angular part of the wave function gives the probability of finding an electron in a particular direction from the nucleus.  The radial dependence and angular dependence of wave function taken together, tell us that a three dimensional standing electron wave (orbital) can be picture to have size, shape, and an orientation of an orbital.
In order to describe the size, shape, orientation of an orbital three quantum number are necessary. 
These quantum number are designed as,
  1. Principal Quantum Number ( n ).
  2. The Orbital angular momentum quantum Number or Azimuthal Quantum Number ( l ).
  3. The Magnetic Quantum Number (ml ).
  4. Spin Quantum Number.

The Principal Quantum Number(n):

    The Principal quantum Number(n) is of primary importance in the determining the size and hence the energy of an electron.
    For hydrogen the energy is fixed by the value of n. In other multi electron atom, the energy of each electron depends on the value of the principal quantum number of the electron. As the value of n increases the radius (nucleus electron separation increases that is the size of the orbital increases).
    The energy also raised, n is always an integer and can assume the value,1,2,3,4.... but not zero.

The orbital angular momentum quantum number or azimuthal quantum number (l):

    The general geometric shapes of an electron wave (Orbital) is described by the Azimuthal Quantum Number. 
    This quantum number related to for the electron in that state.
Thus, l = 0,1,2,3.....(n-1)
Therefore an electron having principal quantum number n, assumed the value l is 0 to (n-1).
Principal Quantum Number(n) Azimuthal Quantum Number(l)
n =1 (K-shall) l=0 (1S)
n =2 (L-shall) l=0 (1S)
l=1 (2P)
n =3 (L-shall) l=0 (3S)
l=1 (3P)

l=2 (3d)

The magnetic Quantum Number:

    The magnetic quantum number associated with the orientation of the electron wave with respect to a given direction, usually that of a strong magnetic fields.
    This quantum number hasn't effect on the shape of orbital or on the energy of an electron.
    For a given Value of l, ml can have any integral value between +1 to -1.
ml = + l, (- 1), (- 2), (- 3) ..... 0 ..... - 1, - 2, - l
Azimuthal Quantum Number(l) Magnetic Quantum Number(ml)
l =0 (S) ml = 0
l = 1 (P) ml = 1, 0, -1
Px, Py, Pz
l = 2 (d) ml = 2, 1, 0, -2, -1
dxy, dxz, dyz, dx2-y2, dz2
    Thus, P - type orbital with three orientation in space describe as PxPy,Pz, and d - type orbital with five orientation in space describe as dxy, dxz, dyz, dx2-y2, dz2.

Spin Quantum Number:

    Besides the three quantum number a fourth quantum number also has forth quantum number namely spin quantum number (s), Was necessary to completely describe an electron in a particular shell.
    The electron itself regarding as a small magnet. A beam of hydrogen atom can be split into two beams by a strong magnetic field. This indicates that there are two kinds of hydrogen atom in which can be differentiates on the basis of their behavior in a magnetic field.
    It has been postulated that each electron spin around it's axis like a lope and they behave like a magnet. A spinning electron can have only two possibilities.
    The electron can either spin clockwise or counterclockwise. The two directions of spin represent as(↑).
    This four quantum number s = 1/2 is independent of other three quantum numbers.
    Two direction of spin is represented as (↑)s can have two possible ms values +1/2 and -1/2 depending on the direction of rotation of the electron about it axis.
    This spin angular momentum is given by,

Shape of The Orbitals:

    The S orbitals penetrate the nucleus most while the P and d orbitals cannot penetrate the nucleus.
    This means that S orbital electron can efficiently screen the nuclear charge from other electrons compared to the other P and d electrons.
    The wave function of the electron in atom is called orbital. The wave function is plotted against distance and the space in three dimensional marked by a curve will gives the shape of the orbitals.
    The probability of finding an electron in space around the nucleus involves two aspects:
  1. Radial Probability.
  2. Angular Probability.
    It is not possible to represent completely in one diagram on paper the directional properties of an electron orbitals. An angular probability distribution must be combined mentally to have an overall shape of the orbital.

Shape of S - Orbital:

    The angular probability distribution are greater interest and importance, an S electron has no angular dependence because the relevant wave function is independent of angles θ and Φ.
    There is therefore an equal chance of discovering the electron in any direction of the nucleus.
How to find quantum numbers of an element?
Angular probability distribution of S orbital.
    With the nucleus at the origin of the Cartesian axes, the sphere of the radius r represents the probability of finding the S electron. An S electron has a spherically symmetrical probability distribution.

Shape of P - Orbital:

    The P orbitals are three orientations is represents as, Px, Py and Pz. The orientations of the orbital plane correspond to ml = 1, 0, -1 are mutually at the right angles.
    So the orbitals designated Px, Py and Pz are mutually perpendicular and they are concentrated along the respective coordinate axis X,Y and Z. Unlike the S orbitals the angular part of the P wave function is dependent on θ and Φ.
How to find quantum numbers?
Angular probability distribution of P orbital.
    The angular Probability distribution are shaped like pears along X, Y and Z axis . Thus in Px orbital it is most likely that the electron will be found in the direction of the X axis. There are no probability of its being found along Y and Z axes.
    Similar results are obtained for the Py and Pz orbitals.

Shape of d-Orbital:

    These orbital arises when n =3 (M - shell), that is the orbitals starts with the 3rd main energy level. When l = 2(d - orbital), ml = -2, -1, 0, 2, 1 indicating that d - orbitals have five orientation, that is, dxy, dxz, dyz, dx2 - y2 and dz2.
    All these five d - orbitals, in the absence of magnetic field, are equivalent in energy and are, therefore, said to be five - fold degenerate.
How to find quantum numbers?
Angular probability distribution of d orbital.

The Beginning:
The history of atomic chronicle must also induce another great discovery, namely ,the Phenomenon of Radioactivity.
In 1896 the French scientist Becquerel, while investigating the nature of the mysterious X -rays discovered by Rontgen a few month earlier, found that a photographic plate wrapped in thick black paper was affected by a sample of potassium - uranyl - sulphate placed over it. In fact, any uranium compound would be effect the plate through covered by paper and kept away from light.
The oblivious conclusion that some radiations emanating from the uranium compound could penetrate through the cover and attack the photographic plate.
This penetrating radiation had its source in uranium itself and Becquerel christened this amazing behavior as Radioactivity. The properties of this radiations were very similar to those of X -rays. 
  1. They were highly penetrating, they effected photographic plates, they would ionize gases and would also induce the fluorescence in some substances.
  2. The rays are not influenced by heat, light or chemical composition.

Discovery of Radioactive Element:

Marie Curie found that the activity of mineral pitchblende was far greater than what was expected of its uranium content. In 1898 Pierre and Marie Curie actually isolated two new elements Polonium and Radium which were more radioactive compared to uranium, the heaviest atom known at the time.
In 1900, Debierne and Giesel discovered actinium which was also radioactive. That the radioactive effects were essentially atomic was recognized early and this helps the isolation to a considerable extent.It was immaterial how uranium and radium chemically combined. The same number of radium atoms will always have the same activity independent of the physical state or the environmental conditions. The phenomenon of radioactivity is associated with atoms which are haviour than lead or bismuth.
The phenomenon of emission of radiation as a result of spontaneous disintegration in atomic nuclei was termed as radioactivity.

The Nature of Radiation:

The radiations emitted by naturally radioactive elements were shown to split by an electric or magnetic field into three distinct parts: Alpha(ɑ), Beta(β) and Gamma(ɣ) Rays.
  • Alpha(α) Rays:
These consist a stream of positively charged particle which carry +2 charge and have mass number is 4.
These particles shown by Rutherford to be identical with, the nuclei of helium atom, that is, these are doubly charged helium ion He+2(atomic number 2, mass number 4).
When an Alpha particle ejected from within the nucleus the mother element loss two units of atomic number and four units of mass number.
92U238 92U234 + 2He4
  • Beta(β) Rays:
These are made up of a stream of negatively charged particles (beta particles). They have been shown to be identical with electrons from a study of their behavior in electric and magnetic fields and from the study of their e/m values (1.77 × 108 coulomb/gm).
The ejection of a beta particle (Charge -1, mass 0) results from the transformation of a neutron (mass 1, charge 0) somewhere at the surface of the nucleus into a proton (mass 1, Charge +1).
0n1 1H1 + -1e0
Neutron Proton β-Rays
When a beta particle is emitted from the nucleus, the daughter element nucleus has an atomic number one unit greater than that of the mother element nucleus.
90Th234  91Pa234 + -1e0
Although beta particles and electrons are identical in their electrical nature and charge/mass ratio, there is a fundamental difference between them.
Ejection of an electron from an atom converts a neutral atom into a positively charged ion but leaves the nucleus undisturbed.
Ejection of a beta particle changes the very composition of the nucleus and produces an atom of the next higher atomic number.
  • Gamma Rays:
These consist of electromagnetic radiation of very short wave length (λ ∼ 0.005 - 1A). These are high energy photons.
The emission of gamma rays accompanies all nuclear reactions.
During all nuclear reactions there occurs a change in the energy of the nucleus due to emission of alpha or beta particles. The unstable, excited nucleus resulting from the emission of an alpha or beta particle gives off a photon and drops a lower and more stable energy state.
Gamma rays do not carry charge or mass, and hence emission of these rays cannot change the mass number or atomic of the mother nucleus.
  • Positrons:
Since the works of the Curies and Rutherford yet another mode of nuclear transformation has been discovered. This involves the ejection of a positron +1e0 from within the nucleus.
This ejection is made possible by the conversion of a proton into neutron.
1H1 0n1 + +1e0
Proton Neutron Positron
The ejection of positron lowers the atomic number one unit but leaves the mass number unchanged.
51Sb120  50Sn120 + +1e0

  • Neutrino:
Breaking down of a neutron into a proton and a beta particle creates a problem with the principle of conservation of angular momentum. Particles like Neutron, Proton and Electron have the spin angular momentum of ±1/2 (h/2π) each. It is thus seen that the equation: 
0n1 1H1 + -1e0

This is not balanced in so far as angular momentum is concerned. If the angular momentum of the proton and the electron are +1/2 (h/2π) they are exceed the angular momentum of the neutron.

If they oppose each other then the momentum become zero in violation of that of the neutron. Pauli therefore postulated that along with the ejected beta particle another tiny neutral particle called neutrino is also ejected. This neutrino has also spin angular momentum of ±1/2 (h/2π). The sum of angular momentum of the particles ejected {say +1/2 (h/2π) for proton, -1/2 (h/2π) for the electron and +1/2 (h/2π) for the neutrino} may now be +1/2 (h/2π) being the same as that of the neutron.
The mass of the neutrino is around 0.00002 with respect to oxygen scale.
Ejection of an electron from within the nucleus should be represented as:

Neutron Proton + Electron + Neutrino
What is radioactivity in chemistry?
Nuclear transmutation example

Characteristics of Alpha, Beta and Gamma Rays:

α - Ray β - Ray Ɣ - Ray
3.1×10-19 C - 1.6×10-19 C Zero
+2e -1 e Zero
Mass (gm):
6.6×10-24 gm 9.1×10-28 gm Zero
4 mH (1/1840) mH Zero
(1.5 - 2.0) ×
109 cm/sec
1010 cm/sec 3×1010

Difference between Nuclear and Chemical reaction:

Nuclear reactions are different from chemical reactions in many respects:
  1. Chemical reactions involves some loss, gain or overlap of outer orbital electrons of the reactant atoms. Such reactions cannot alter the composition of the nuclei, so that the atomic number of the chemical reactions unchanged.
    CH4 + H2O CO + 3H2
    On the other hand Cause of Nuclear Decay involves emission of alpha particles, beta particles or positrons from inside the nucleus, which leads to change in atomic number of the nucleus.
    51Sb120  50Sn120 + +1e0
    In some artificially induced Radioactive decay reactions, neutrons are absorbed by target nucleus producing an isotopes. Nuclear reactions therefore leads eather to the birth of another element or produce isotopes of the parent element.
  2. The nuclear reactions are accompanied by energy changes which far exceed the energy changes in chemical reactions.
    For example, the energy evolved in the radioactive transformation of one gram of radium is five hundred thousand times as large as the energy released when one gram of radium combine with chlorine to form RaCl2.

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