Chemistry: 'Structure of the Atom'

its the third chapter of chemistry.

Founder of the Electron

J.J Thomson

Founder of the Proton

E. Goldstein - 1886

How did E. Goldstein discover the Proton?

He saw new radiations in a gas discharge and found out that these were positively charged.

representation of an electron

e-

representation of a proton

p+

charge of an electron

-1

charge of a proton

+1

mass of a proton

1 unit

failure of Dalton’s atomic theory

The discovery of sub atomic particles called protons and electrons

Thomson’s model of an atom

(i) An atom consists of a positively charged sphere in which electrons are embedded into.
(ii) The negative and positive charges in an atom is equal in magnitude. So, the atom is electrically neutral.

disadvantage of Thomson’s model

It could not explain the properties of atoms.

Rutherford’s gold foil experiment

high speed alpha rays were made to hit the gold foil

expectations of Rutherford

most of the alpha rays would hit the fluorescent screen without any problem and only some would slightly deviate from it’s path

observation of Rutherford’s experiment

(i) most of the alpha rays passed through the gold atoms.

(ii) some deviated from it’s path.

(iii) one out of every 12000 particles rebounded.

conclusions of Rutherford’s experiment

(i) most of the space inside the atom is empty.

(ii) the positive charge of the atom occupies very little space.

(iii) the positive charge and the mass of the gold atom occupies very little space.

Rutherford’s nuclear model of an atom

(i) Positively charged center called the nucleus.

(ii) The nucleus takes up most of the mass of the atom.

(iii) The electrons revolve around the nucleus in circular path.

(iv) The size of the nucleus is very small compared to the size of the atom.

drawbacks of Rutherford’s experiment

(i) any particle which revolves in a circular path, accelerates.

(ii) so, the electron would radiate energy while accelerating.

(iii) then, the electron would lose it’s energy.

(iv) so, the electron would fall into the nucleus.

(v) hence, matter should not be existing as it does today.