What is the World Made of? 450 BCE Empedocles Matter was composed of 4 elements: Earth Water Air Fire

Democritus 400BCE Stated that matter was made up of tiny particles that cannot be broken down.

Alchemists 500 -1600 CE Attempted to change lead into gold. Looked for a substance that would give them eternal life. Many died drinking mercury

Robert Boyle- 1650 “An element is a pure substance that cannot be broken down into simpler substances.”

Joseph Priestly- 1700 First person to isolate oxygen. Discovered that air must be a mixture.

Models of Atomic Structure

John Dalton’s Model 1800’s All matter is made up of atoms which are too small to see Each element has its own kind of atom. Atoms of different elements are different. Compounds are created when atoms of different elements link to form molecules.

Michael Faraday -1800 Charged atoms are called ions Matter must contain positive and negative charges Opposite charges attract, and like charges repel

The Thomson Model 1897 Called the “raisin bun" model. The atom is composed of a positively charged material with the negatively charged electrons scattered through it.

The Rutherford Model 1911 An atom is mostly empty space. Discovered the nucleus of an atom A small, positive nucleus with the negative electrons scattered around the outside edge. Gold foil experiment

The Bohr Model 1913 Electrons move in definite orbits around the nucleus, like planets. Electrons are in specific orbits called “energy levels”.

The Quantum Model Electrons have NO definite path in an atom. The more energy an electron has, the farther from the nucleus they are. The small, positively charged nucleus is surrounded by a large space.

Scale of the atom the nucleus is ten thousand times smaller than the atom the quarks and electrons are at least ten thousand times smaller