The document introduces several historical models of the atom: Thomson's "plum pudding" model, Rutherford's nuclear model with electrons orbiting a dense nucleus, Bohr's model incorporating allowed electron energy levels, and the modern electron cloud model showing the probabilistic distribution of electrons rather than definite orbits. It notes key characteristics of protons, neutrons, and electrons - their relative charge and size, and roles in determining atomic number and mass.

1. Introduction to the Atom

2. Thomson’s ModelNegative charges spread throughout a ball of positive charge

3. Think: berries in a muffin where the berries are the negative chargeRutherford’s ModelThe atom is mostly empty space

4. Has a positively charged center NUCLEUS

5. Negatively charged electrons orbit in fixed paths around the nucleus

6. The positively charged nucleus later known to contain PROTONSBohr’s ModelBohr revised Rutherford’s model

7. Electrons can have only specific amounts of energy

8. Electrons orbit in a flat layer.

9. Resembles planets orbiting the sun, or the layers of an onionElectron Cloud ModelElectrons do not orbit like planets, but exist in a cloud.