History of the Atom

1. Democritus

a) 1st idea of atom – smallest particle

The Greeks (~2500yrs ago)The Greeks (~2500yrs ago)

2. Aristotle

a)Observations, no experimentation

b)All matter made up of 4 elements:

Air, water, fire earth

2. Antoine La Voisier 1743-1794

a) Discovered several elements

b) Worked with law of conservation of mass

c) Considered the Father of Modern Chemistry

d) Beheaded during French Revolution

3. John Dalton (1766 - 1844)

a) Atomic Theory

1. Atoms are indivisible

2. All atoms of same element are identical BUT different than atoms of same element

3. Atoms combine in simple whole # ratios

4. Chemical rxns occur when atoms combine, split or rearrange

4. Thomson, Sir J.J. (1856-1940)

a) Cathode ray tube experiment (aka… raison bun or plum pudding model)

1.Set up a glass tube, free of air with magnets on each side

2.Sent a stream of particles thru it and observed which way they were deflected

3. Credited with discovery of electrons

5. Ernest Rutherford

1871-1937

1. Set up screen with thin Au foil in front

2. Shot stream of alpha particles (42He) thru

3. Most particles went straight thru, few deflected

4. Since 42He is + charge, once deflected, it’s off

of something else +5. Credited with discovery of nucleus with +

charge due to protons

a) Gold Foil Experiment

6. James Chadwick

a) Discovered neutron1. Same mass & location as

proton

a) Solar system model of the atom1. Electrons orbit nucleus in orbits called

ENERGY LEVELS 2. Quantum – bundle of energy that an

e- needs to change level3. When e- change levels – not stable,

they fall back towards nucleus & release energy in form of light that we see as colors (ROY G BIV)

7.Neils Bohr 1885-1962

8. Schrödinger

a) Quantum Mechanical Model

1. Deals with probability of where the electron is most likely located… Near the nucleus