Dalton

What They Knew by1800

• Elements were defined as substances which could not be broken down further by chemical means. (Lavoisier 1775)

• There was a law of definite proportions (elements for a given compound always combined in the same ratio)

• There was a law of conservation of mass. (In a chemical reaction mass is never created or destroyed.

John Dalton• Was born in 1766

• Was a school teacher and later a University Professor

• Used pre-existing laws and his own experiments to come up with the first atomic theory

• Came up with the first modern atomic theory

Dalton’s Atomic Theory 1808

• All matter is made up of small particles called atoms.

• Atoms cannot be created or destroyed, or cut into smaller particles

• All atoms of the same element are identical in mass and size, but they are different in mass and size from the atoms of other elements.

• Compounds are created when atoms of different elements link together in definite proportions

Billiard Ball Model• The atom, according to Dalton, was

much like a tiny billiard ball.• An element is a substance made up

of many very tiny particles (or many tiny billiard balls) which are all identical.

• You could physically cut large chunks of element into smaller pieces (like cutting small chips of Iron off an anvil) but you could not chemically break that element apart.

Relative Masses

• Using electrolysis of water Dalton found that the mass of evolved oxygen was always 8 times that of evolved hydrogen.

• He reasoned that because Hydrogen was the lightest element (known), he could measure the relative masses of all the known elements in relation to Hydrogen

• Dalton had symbols for all the known elements, as well as a very primitive table for showing the elements in order of increasing atomic mass.

Last Facts

• Dalton was a reclusive character• He rarely read any writings from other scientists

because he believed that they might “lead him astray”

• He never got married• 40,000 people came to his funeral• He was colour blind• He had a weather diary with 200,000 entries

from the time he was 22 to the time he died.