1. Atomic Structure
Topic 3

2. History John Dalton JJ Thompson Hard sphere model Earliest model
No internal structure
JJ Thompson
Plumb Pudding model
+ and – charges in nucleus
Supported existence of negative particles

3. Earnest Rutherford Bohr’ model Many scientists Empty space model
Small dense nucleus
Electrons revolve around nucleus
Bohr’ model
Electrons in specific orbits
Orbits have fixed energy
Electron shells
Many scientists
Wave mechanical (electron cloud)
Electrons in orbital
Orbital – area an electron is likely to be found

4. Atomic Structure Atom – basic unit of matter Mostly empty space
Composed of much smaller particles
Protons (+)
in nucleus
mass = 1 amu
Atomic number
Neutrons (o)
In nucleus
Mass = 1 amu
Atomic mass – atomic number = number of neutrons
Electrons (-)
In orbitals
Mass = 1/2000 of proton [1/1836]
In a neutral atom = same as number of protons

5. Nucleus Mass number Small, dense Mass of atom (neutron plus protons)
Contains protons and neutrons (nucleons)
Nuclear charge is (+) contains protons
Mass number
Identifies isotopes of the same element
neutrons plus protons
Total number of nucleons