Topic 1B: Atomic Theory, 4 Major Steps

Question 1

John Dalton

Answer 1

The Billiard Ball Model
- atoms are indivisible
- all atoms of an element are identical
- elements can’t have the same mass

Question 2

JJ Thompson

Answer 2

Plum Pudding/Chocolate Chip Cookie Model
- discovered that electrons are embedded in a positively charged sphere
- atoms are made of subatomic particles

Question 3

Ernest Rutherford

Answer 3

Planetary Model
- Discovered the proton
- atoms are mostly empty space and are positively charged at the centre (<— the nucleus)

Question 4

Niels Bohr

Answer 4

Energy Level Model
- electrons don’t randomly orbit but move in circular orbits of electron shells
- electrons move between shells by gaining/losing energy

Question 5

Proton

Answer 5

• found in the nucleus
• charge of 1+
• each atom of an element will have the same number of protons - determines the element

Question 6

Neutron

Answer 6

• found in the nucleus
• no charge (neutral)
• numbers can be different in atoms of the same element, also called isotopes

Question 7

Electrons

Answer 7

• found in specific energy levels around the nucleus
• charge of 1-
• the number of electrons per atom can be changed, also called ions

Question 8

Mass Number

Answer 8

• Found by adding protons and neutrons together for a specific atom
• Neutron number can be found by subtracting the atomic number from the mass number
  (Ex - Oxygen: 16-8=8)