History of the Atom

Question 1

Democritus

Answer 1

• Developed the idea of atoms

- Called the smallest possible bit of matter Atoms, after the Greek word atomos

Question 2

John Dalton: The Billiard Ball Model

Answer 2

• All matter consists of atoms, which cannot be broken up
• Each element composed of the same kind of atoms, with the same mass and behaviour. Different elements have different atoms
• When atoms combine to form compounds, they do so in fixed ratios
• Chemical reactions are rearrangement of atoms (mass is conserved). Atoms cannot be created or destroyed

Question 3

JJ Thompson: The Plum Pudding Model

Answer 3

Saw the atom as:

• A positive sphere with negatives embedded in it
• the atom was electrically neutral
• He believed the mass of the atom was due to the electrons

Question 4

Ernest Rutherford: The Nuclear Model

Answer 4

• over 99,9% of the mass of the atom must be concentrated in a tiny nucleus at its centre
• The nucleus must be positively charged
• The rest of the atom’s volume was taken up by the circling electrons

Question 5

Niels Bohr: The Planetary Model

Answer 5

• Electrons in an atom may only travel in a few fixed paths around the nucleus
• While travelling in their fixed paths the electrons cannot radiate or absorb energy
• He called the regions of space where electrons have fixed energies, energy levels
• Lowest energy levels = ground state
• Electron gains enough energy = quantum jump = now excited state
• Check book

Question 6

Schrodinger: The Wave Mechanical model

Answer 6

• Replaced Bohr’s orbits with orbitals (Under definitions)