History of the Atom and Naming

Aristotle’s Contributions

Gave basic idea of atom

added qualities (heat, light, cold, moisture)

Thought all matter was made of four elements (Earth, water, fire air)

Democritus’ Conrtibutions

Greek Philosopher

Idea of ‘atomos’ (indivisible)

No experiments to support idea

Democritus’ Model



No protons, electrons, or nuetrons

Solid and;Indestructible


Law by Lavoisier

Conservation of Mass-

Mass is neither created nor destroyed during basic chemical reactions


Law by Proust

Law of Definite Proportions-

The fact that a chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample or source of the compound

Law by Dalton

Law of Multiple Proportions-

If two or more different compounds are composed of the same two elements, then the ratio of the masses of the second element combined with a certain mass of the first element is always a ratio of small whole numbers


D(all)(ton)- All of the proportions/ tons of proportions=

Law of MULTIPLE Proportions

John Dalton’s Atomic Theory of Matter


All matter is made of atoms (atoms are indivisible and indestructable)

All atoms of a given element have identical masses and properties

Compounds are formed by a combination of two or more different kinds of atoms (Law of Constant Proportions)

A chemical reaction is a rearrangement of atoms

J.J. Thompson’s Results

He knew that…

Atoms of any element can be made to emit tiny negative particles

ALL atoms must contain these negative particles

Atoms do not have a negative net charge so there must be something balancing the negative charge


Cathode Ray Tube

Set up so electric current runs through a tube

light moves from positive end to negative end

When magnets were added the light bent, and still went from + to –

Showed that….

– and – repel

– and + attract

Showed negative charge in atom called electron

William Thompson;

(Lord Kelvin)’s



Negative Electrons Were Embedded into a positively charged spherical cloud


Lord Kelvin’s Model

Plum Pudding Model

(positive cloud, negative electrons)

Earnest Rutherford’s Experiment

Gold Foil Experiment

What he Expected:                            Actual Results:

The particles to pass through         Most passed through

without much change in direction     because the atom is

because the positive charges          mostly empty space

were spread out evenly              but some were deflected



Conclusions of the Gold Foil Experiment

Atom mostly empty space

Nucleus has + charge

Electrons float around the nucleus

Rutherford’s Model of the Atom

Dense nucleus made of protons and nuetrons

Electrons orbit the nucleus

Niels Bohr’s Model

Electrons had a distinct orbit around the nucleus

Looks like the Jimmy Neutron logo

nucleus in the middle

electrons orbit the nucleus on the energy fields

Present Model

Charge- Cloud Model

electrons occupy orbitals around the nucleus determined by their energy levels

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