Atomic Structure ~

Page 1

Atom was divided into three particles-

Proton-positive charge

Neutron-neutral charge (0)

Electron-negative charge

First,

J J Thomson discovered the electron by cathode rays experiment. By the same experiment, Eugen Goldstein discovered the proton

Neutron discovered by James Chadwick. The mass of the atom was not totally accounted by the proton,

Thomson gave a model like a Christmas pudding

Rutherford conducted an experiment by passing alpha particles through a thin gold foil. It had spectacular and unexpected results.

Very less particles were deflected so nucleus of an atom was very small and dense.

Rutherford then gave his own model somewhat like the one below. But it had a fault as then the electrons would fall into the nucleus. So Neil Bohr gave his revised model

This new model said that they do not lose energy while revolving so they do not fall into the nucleus.

Atomic number

Number of protons in an atom. Actually protons=electrons in a stable atom.

Mass number

Sum of the number of protons and neutrons (together known as nucleons.

Shells of an atom go on as K L M N O....

Capacity of each shell is given by the formula

2n(squared)

for 1st shell

2 times 1 times 1

=2

for 2nd,

2 times 2 times 2

=8

and so on

Electrons always fill the lower shells before moving on the next ones.

The outermost shell of an atom cannot accomodate more than 8 electrons

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