The Development of a Modern Theory of the Atom

Democratus (460-370 B.C)

•Matter is composed of small, indivisible particles called atomos.

AristotleMatter is continuous - there is no smallest piece

Who was right?

John Dalton (published 1803-07)

1.Elements are composed of atoms2. All atoms of a given element are

identical; 3. Atoms of different elements are

different4. Atoms of an element are not

changed by chemical reactions5. Compounds are formed when

atoms combine6. Led to the law of conservation of

mass 7. Law of multiple proportions:

Law of Conservation of Mass

Matter is neither created or destroyed.

How does this lead to the balancing of equations?

Law of Multiple ProportionsWhen two elements form a

series of compounds, the ratios of the masses of the second element that combine with 1 gram of the first element can always be reduced to small whole numbers.

Example: Nitrogen and oxygen combine in several

different ratios.Mass of Nitrogen that combines w/ 1g of oxygen

compound a 1.750 g compound b 0.8750 g compound c 0.4375 g

1.750 = 2 ; .875 = 2 ; 1.750 = 4 .8750 1 .4375 1 .4375 1

The Cathode Ray TubeThe Cathode Ray Tube

corpuscles

Partial vacuum

Thomson (published 1897)Charge to mass ratio for electrons

1.76 x 108 C/g

Thomson Model of the AtomThomson Model of the Atom

Plum pudding model

Positive doughNegative raisins orcorpuscles

Millikan's Oil Drop Experiment

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Millikin’s Oil drop experiment (published 1909)

charge of electron = 1.60 x 10-19C

Millikan’s Oil Drop Experiment (Published in 1909)

Combining Millikins and Thompsons work we get

1.6 x 10-19C

1.76 x 108 C/g= 9.11 x 10-28g

The mass of one electron

Rutherford’s First experiment (1871-1937)

electrons

energy

Helium nuclei

24He

Gold Foil Experiment

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Rutherford’s Gold Foil Experiment (1910)

If the nucleus were blown up to the size of a tennis ball and placed on the fifty yard line of our football field where would the first electron be found?

It would be a firefly cruising out past brownroad.

So what is an atom mostly?

NOTHING!

So what are you mostly?

NOTHING!

What are the fundamental particles that make up an atom?

Protons - positive charge of 1 and a mass of 1 amuNeutorns - no charge and a mass of 1 amu

Electrons - negative charge of one and a mass of 1/1800 amu

What are protons and neutrons made of?

Quarks

What are quarks made of?Strings

What do you get when a string is unbound?

So what are protons and neutrons mostly?

NOTHING!

Energy E = mC2

What would happen if two atoms were brought into proximity of each other?