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Scientist to propose the atomic theory

Dalton

1

What are the 4 postulates of the atomic theory?

1. elements are composed of Atoms
2. All atoms of an element are identical, different from other elements (first part not true!)
3. In chemical reactions Atoms are not changed into different types of Atoms. Atoms are neither created nor destroyed.
4. Compounds are formed when Atoms of all elements combine

2

Law that states the relative kinds and numbers of atoms are constant for a given compound.

Law of constant composition

3

During a chemical reaction, the total mass before reaction is equal to the total mass after reaction.

Law of conservation of mass

4

Law that states if two elements A and B combine to form more than one compound, then the mass of B which combines with the mass of A is a ratio of small whole numbers

Law of multiple proportions

5

Scientist that was credited with discovering the electron in the cathode ray experiments.

J.J.Thompson

6

Oil-drop experiment and the mass of an electron.

Millikan

7

Becquerel and radioactivity

Some substances spontaneously emit high energy Rays.

8

Rutherford

Radiation experiments

9

Chadwick

Discovered the neutron

10

Isotopes

Differ in the number of neutrons

11

Atomic number

Number of protons in the nucleus.

12

Mass number

Total number of nucleons in the nucleus.(protons and neutrons)