Atomic Theory

Date

Democritus• Date 460-370 B.C.• Democritus was a philosopher; did

no research• He thought that everything was

made up of tiny round things called atoms.

• Atoms are the building blocks of life.

John Dalton• 1787 – 1844• Wanted to learn in what ratios

different elements combine in chemical reactions.

• Through experimentation devised his atomic theory.

Dalton’s Atomic Theory1. Elements are composed of

submicroscopic indivisible particles called atoms.

2. All atoms of a given element are identical. Atoms of different elements are different from one another.

Now that we know about subatomic particles this point is no longer valid.

Now that we know about isotopes, this point is not entirely valid.

3. Atoms of one element can mix or chemically combine with atoms of other elements, creating compounds with simple whole-number ratios.

animation of Dalton's 3rd point4. Chemical reactions occur when

atoms are separated, joined or rearrange.

Na+ OH- H+ Cl-

Reactants

Na+

OH -

H +

Cl -

Energy used to break bonds

Na +

OH -

H +

Cl -

Atoms rearrange

Na +OH -H +

Cl -

Atoms join

Technically, not atoms, but ions that join and break apart

JJ Thomson• Found electron• Used cathode ray tube

– Beam bent away from negative magnet– cathode ray tube in action

• “Plum Pudding” or “Chocolate Chip Cookies” model

Robert Millikan• Determined the electrical charge of

electron• “Oil Drop Experiment”

– Suspended oil in mid-air– Millikan's experiment explained– What Milikan saw– Milikan's experiment set to music

• Still plum pudding model

• Basic sketch of his experiment

• Still plum pudding model

Eugene Goldstein

• Found the proton• Reverse cathode ray tube

– Looked at ray going to anode• Still plum pudding model

Ernest Rutherford • Found nucleus• The Gold Foil Experiment• Atom is mostly empty space – first nuclear

model

• Rutherford Halo Style• Bill Nye the atom

James Chadwick

• Found neutron • Shot alpha particles at Be nucleus• Nucleus is made of two particles

– Positive protons– Neutral neutrons

electron

neutron

proton

Niels Bohr• Reasoning for Bohr's model• Planetary model• Proposed electrons have a set amount of

energy putting them in different energy levels, or orbits around the nucleus.

• Electrons can change energy levels; higher energy levels are further from the nucleus.

Heisenberg• Heisenberg’s uncertainty principle:

cannot know exactly both the velocity and position of electron at the same time.

• Heisenberg's uncertainty principle explained

• Like trying to catch a helium balloon in the dark.

Schrödinger• Electron cloud gives a 90%

probability of finding the electron within the darkly shaded area.

• Electrons move like moths around a light – unpredictable.

• example project – rap w/o words• example 2 – good idea, but do spell check,

make sure people can read the words (speed and color)

• phenomenal example – this is the ideal project• atom rap – no pictures, but at least you can

read the words.