Atomic Structure: Fundamental Particles - Atomic Models

Question 1

Democritus

Answer 1

• 450BC
• Greek philosopher that speculated that everything is made up of tiny particles
• Called them atomos/atoms, meaning ‘indivisible’
• Theory ignored for 2000 years

Question 2

John Dalton

Answer 2

• 1803
• Re-introduced idea of tiny particles and calls them atoms
• Hard, solid spheres that cannot be split
• Different spheres made up different elements
• Can join together

Question 3

JJ Thompson

Answer 3

• 1897
• Discovered the electron
• Created plum pudding model, atom is ball of positive charge with negative electrons embedded in it

Question 4

Ernest Rutherford

Answer 4

• 1907
• Discovered protons
• Fired charge alpha particles at thin gold foil (most went through, but a few bounced back)
• Led him to create the nuclear model (mass of atom concentrated in centre, the nucleus, which is positively charged)
• Most of the atom is empty space

Question 5

Niehls Bohr

Answer 5

• 1913
• Adapted Rutherford’s model with four new basic principles:
• Electrons only exist in fixed orbits (shells) and not anywhere in between
• Each shell has a fixed energy
• When an electron moves between shells electromagnetic radiation is emitted or absorbed
• Because energy of shells is fixed, the radiation will have a fixed frequency

Question 6

James Chadwick

Answer 6

• 1932
• Discovers neutrons
• Discovers that neutrons weigh the same as protons but have no electrical charge