Atomic Structure Timeline

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Slide 1

Atomic Structure Timeline

Use the following information to complete the lecture handout.

On tomorrow’s quiz, you will be expected to…

draw the atomic models

match scientists to their experiments and discoveries

place the models in chronological order

Slide 2

Democritus (400 B.C.)

Proposed that matter was composed of tiny indivisible particles

Not based on experimental data

Greek: atomos

Slide 3

Alchemy (next 2000 years)

Mixture of science and mysticism.

Lab procedures were developed, but alchemists did not perform controlled experiments like true scientists.

Slide 4

John Dalton (1807)

British Schoolteacher

based his theory on others’ experimental data

Billiard Ball Model

atom is a uniform, solid sphere

Slide 5

John Dalton

Dalton’s Four Postulates

1. Elements are composed of small indivisible particles called atoms.

2. Atoms of the same element are identical. Atoms of different elements are different.

3. Atoms of different elements combine together in simple proportions to create a compound.

4. In a chemical reaction, atoms are rearranged, but not changed.

Slide 6

Henri Becquerel (1896)

Discovered radioactivity

spontaneous emission of radiation from the nucleus

Three types:

alpha () - positive

beta () - negative

gamma () - neutral

Slide 7

J. J. Thomson (1903)

Cathode Ray Tube Experiments

beam of negative particles

Discovered Electrons

negative particles within the atom

Plum-pudding Model

Slide 8

J. J. Thomson (1903)

Plum-pudding Model

positive sphere (pudding) with negative electrons (plums) dispersed throughout

Slide 9

Ernest Rutherford (1911)

Gold Foil Experiment

Discovered the nucleus

dense, positive charge in the center of the atom

Nuclear Model

Slide 10

Ernest Rutherford (1911)

Nuclear Model

dense, positive nucleus surrounded by negative electrons

Slide 11