Answer the following
A. Whati is the difference in the atomic models of Thomson and Rutherford ?
B. What is meant by valency of an element ? what is the relationship between the number of valence electron and valency ?
C. What is meant by atomic mass number ? Explain how the atomic number and mass number of carbon are 6 and 12 respectively.
D. what is meant by subatomic particle ? give brief information of three subatomic particles with refrence to electrical charge, mass and location.

a. Difference between Thomson and Rutherford Theory are as follows :

Thomson Theory	Rutherford Theory
States that electron are embedded in a positively charged solid material which is spherical in shape	States that an atom is composed of an atomic nucleus around which electrons are revolving in an orbit
Does not give any detail about the atomic nucleus	Explains about the atomic nucleus
States that electrons are uniformally distributed in an atom	States that electrons are located around a central solid material
Indicates that atom is spherical in shape	Indicates that an atom has a central solid core called as nucleus surrounded by the electrons
Does not give any idea about constituents of nucleus	States that nucleus is composed of protons and neutrons

b. Valency of an element : It is the number of electrons of an atom of the element uses to combine with atoms of other elements.
It is the combining power of an atom of the element.
Valency of an atom is determined by its electronic configuration.
It gives idea about the number of electrons loss or gain in order to achieve the nearest noble gas configuration.
For example: Na(11) = 2,8,1 So, its valency is 1
Cl(17) = 2,8,7 So, its valency is also 1

Number of valence electron : It is defined as the number of electrons present in the outermost shell of an atom.
It is not necessary that all the valence electrons take part in bonding.
For example: Na(11) = 2,8,1 So, its number of valence electron is 1
Cl(17) = 2,8,7 So its number of valence electron is 7

It can be seen that valency of an element is related to number of valence electrons in that atom.


c.Atomic Mass Number : It is the sum of total number of protons and neutrons present in a nucleus.
Atomic mass number = number of protons + number of neutrons.
Atomic number = number of protons = number of electrons. It is denoted by Z.
Mass number = number of protons + number of neutrons. It is denoted by A.
For example : Carbon atom its, Number of proton = 6
Number of neutrons = 6
Number of electron = 6
Atomic number(Z) = number of protons = number of electrons = 6.
Mass number(A) = number of proton + number of neutrons = 6 + 6 =12.

d.Subatomic particles : A subatomic particle is a structural and functional unit of the matter. That means all the matters are made up of these fundamental particles. According to modern atomic theory, an atom has a nucleus, which is present in its center or core. These nucleus contain subatomic particles like protons and neutrons.
Difference between subatomic particles are as follows :

Electron
1. Electrons are present outside the nucleus of an atom.
2. Electrons are negatively charged that is ($1.6\times {10}^{-19}$coulomb).
3. The mass of an electron is considered to negligible. It is 1800 times less than that of a hydrogen
4.Relative mass = 1/ 1840 times hydrogen
5. It revolves around the nucleus in the discrete orbit.

Proton
1. Protons are present in the nucleus of an atom.
2. Protons are positively charged that is ($1.6\times {10}^{-19}$coulomb).
3. The mass of a proton is approximately 1u(1Dalton) that is ($1u=1.66\times {10}^{-27}g$).
4. They are closely bound in the nucleus.

Neutron
1. Neutrons are present in the nucleus of an atom.
2. Neutrons are neutral.There is no charge.
3. The mass of a neutron is nearly equal to the mass of a proton that is 1u(1Dalton) that is ($1u=1.66\times {10}^{-27}g$).
4. They are closely bound in the nucleus.