THE ATOM AND THEIR THREE MODELS

JOHN DALTON MODEL

DALTON THEORY

1. Matter is made up of tiny indivisible particles called atoms.

2. There are different kinds of atoms that are distinguished by their mass and their properties. All the atoms of an element have the same chemical properties. The atoms of different elements have different properties.

3. The compounds are formed by combining the atoms of two or more elements in fixed and simple proportions. So in a compound those of atoms of each type are in a relation of integers or simple fractions.

4. In chemical reactions, atoms are exchanged from one substance to another, but no atom of one element disappears or is transformed into an atom of another element.

THOMSON MODEL

THOMSON THEORY

1. J. J. Thomson, who discovered the electron in 1897, proposed the plum pudding model of the atom in 1904 before the discovery of the atomic nucleus in order to include the electron in the atomic model.

2. In Thomson's model, the atom is composed of electrons surrounded by a soup of positive charge to balance the electrons' negative charges, like negatively charged "plums" surrounded by positively charged "pudding".

3. The 1904 Thomson model was disproved by Hans Geiger's and Ernest Marsden's 1909 gold foil experiment.

RUTHERFORD MODEL

rutherfoRD THEORY

1. Major portion of the atom is empty.

2. The whole mass of the atom is concentrated in the center of atom called nucleus.

3. The positively charged particles are present in the nucleus of atom.

4. The charge on the nucleus of an atom is equal to (+z.e) where Z= charge number, e = charge of proton.

5. The electrons revolve around the nucleus in different circular orbits.

6. Size of nucleus is very small as compare to the size of atom.

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