Unit 2 Atoms & Atomic Theory

Elements

Pure substances with only one type of atom

Compounds

Two or more elements chemically bonded in a fixed ratio. Only a chemical reaction can pull them apart

Mixture

Two or more different elements not chemically combined

Homogeneous mixture

A mixture that is the same throughout

Heterogeneous mixture

A mixture that is not the same throughout

Theory

To explain a complex natural process

Law

To describe occurrences in nature

Billiard ball model

Created by John Dalton, the first atomic model, discovered the weight of gases

Plum Pudding Model

Created by J.J Thompson, discovered electrons and protons, bending cathode rays

The Nuclear Model

Created by Ernest Rutherford, discovered the nucleus, atom was empty space

The Planetary Model

Created by Niels Bohr, discovered electrons moved in orbitals around the nucleus

The Electron Cloud Model

The most current model, electrons do not move in precise rings

Limitations of the Bohr model

Electrons do not travel in perfect rings

Does not work well for larger atoms

Limitations of the cloud model

Does not show energy levels/shells

Makes it harder to show how many electrons in each shell

Does not show protons and neutrons specifically

The Nature of Science

New discoveries/information are presented