The history of the atom

Question 1

Describe ‘atomic theory’ (4)

Answer 1

• Everything is made up of tiny spheres which can’t be broken down further
• the smallest possible unit of matter
• they are separated by empty space
• Democritus in 500 BC

Question 2

Describe ‘solid spheres’

Answer 2

• John Dalton in the 1800s
• different types of spheres might make up different elements

Question 3

Describe ‘plum pudding model’

Answer 3

• JJ Thomson (1897)
• theorised that an atom is a ball of positive charge, with negative electron mixed throughout it
• called in plum pudding model

Question 4

Describe ‘nuclear model’

Answer 4

• Ernest Rutherford (1909)
• In Rutherford’ experiments, alpha particles were fired at a thin sheet of gold foil
• Most particles passed through, but some were deflected off course
• This caused him to hypothesise that there was a dense region of positive charge at the centre of the atom that repelled the alpha particles
• As a result he developed the nuclear model of the atom, in which there was a central positive nucleus, surrounded by negative electrons

Question 5

Electron shells

Answer 5

• 1913: Niels Bohr
• Suggested electrons orbited the nucleus in shells
• this prevents the atom from collapsing

Question 6

Protons and neutrons

Answer 6

• 20th century
• Rutherford: discovered protons
• James Chadwick: discovered neutrons