Rutherford model of atom- IN 1911 Rutherford his coworkers performed a series of experiment known as scattering experiments. He bombarded X particles or thin gold foil (i.e. 100 mm thick). He observed following results.

1. Most of the X-particles (99.9%) pan through there + produce bright spot on screen.
2. Few particles were deflected at different angles.
3. Very few particles (one in 20000) were deflected from the above observation, Rutherford made following conclusions.

1. Since most of X-particle could pan through them it shows that most of the pace in an atom is hollow.
2. Few particles were deflected from their path it must be concluded that inside an atom a heavy positive charged mass present in 94 atom. Moreover this mass must be occupied in very small space in atom
3. Bouncing back of X-particle from the foil indicate that the direct collision with the heavy positive charge mass, which is extremely small as compared to total volume of atom.

Features of Rutherford model

1. Atom consist of 2 parts (a)Nucleus (b)extra nuclear part.

Nucleus is present in centre + space around the nucleus called extra nuclear part.

2. Two size of  nucleus is very small as compared to extra nucleus part(10^-10m)
3. The entire mass of an atom is due to nucleus which contains Proton and Neutrons while electrons present in extra nucleus part with negligible mass.
4. Electrons in extra nuclear portion are not stationary and are revolving around the nucleus in a circular orbits. They are also called planetary electrons.
5. The force of attraction of electron with the nucleus is balanced centrifugal force acting away from the nucleus thus electron do not leave their orbits.

Atomic no = no. of proton in nucleus

(proton no) = no. of electron in natural atom

Mass no = no. of proton + no. of neutrons.

Nucleus – proton + neutrons present in nucleus no mass no nearly equal to atomic mass

Mass – not a whole number

Mass number – always whole number

Isotopes –atoms of same element having same at no. but different mass no. are called Isotopes

                ¹₁H, ²₁H, ³₁H (protium, deuterium & tritium )   

Isobar- atoms of different elements possess same mass no.

                ⁴⁰₁₈Ar, ⁴⁰₁₉K, ⁴⁰₂₀Ca (differ in no. of P+N )

Isotones- atoms of different elements which contain the same no. of neutrons called isotones. (differ in

                at no. + mass no.)

                ¹⁴₆C, ¹⁵₇N, ¹⁶₈O (each of then contains 8 neutrons )

Isoelectronics – atoms or Ions containing same no. of electrons are called Isoelectronics.

                N^---, O^--, F^-, Na⁺, Mg⁺⁺,Ai⁺⁺⁺,Ne  Each contains 10 electrons.