8. Nuclear and Particle Physics

Question 1

How has the understanding of atomic structure changed overtime?

Answer 1

Dalton’s ‘Billiard Ball’ Model 1803
J.J Thompson’s Plum Pudding Model 1897
Rutherford’s Gold Foil Experiment 1909-1911
Neil Bohr’s Model 1913
Quantum Mechanical Model 1926

Question 2

What’s Dalton’s ‘Billiard Ball’ Model 1803?

Answer 2

Imagined all matter was made of tiny solid particles called atoms
No-one believed him for years, as they thought everything was fire, earth and water

His model proposed:
- Atoms are the smallest constituents of matter and cant be broken down any further
- a given element has identical atoms
- different elements have different atoms
- When chemical reactions occur, atoms rearrange to make different substances

Question 3

What’s J.J Thompson’s Plum Pudding Model 1897?

Answer 3

Discovered the electron
Proposed the Plum Pudding Model:
- atom consists of positive and negative charges in equal amounts, so neutral overall
- spheres which are positively charged with uniformly distributed charge and density, making a ‘plum pudding’

Question 4

What’s Rutherford’s Gold Foil Experiment 1909-1911?

Answer 4

Hans Geiger and Ernest Marsden set out to test the plum pudding model:
- Walls of zinc sulphate which emitted light when hit, this needed a microscope to see
- Positively charged alpha, α particles were aimed at very thin gold foil

Most went straight through, only some were deflected and only some were completely deflected in other direction

The results stated:
- Atoms have a central, positively charged nucleus containing the majority of mass
- Most of the atom is empty space
- electrons orbit the nucleus

Question 5

What’s Neil Bohr’s Model 1913?

Answer 5

Bohr improved Rutherford’s planetary model
- Showed electrons occupy shells or energy levels around the nucleus
- these are a particular distance away from the nucleus and they cant exist between

Question 6

What’s the Quantum Mechanical Model 1926?

Answer 6

Ervin Schrödinger used equations to calculate the likelihood of finding an electron in a certain position

Portrayed as a nucleus surrounded by an electron cloud. Where the cloud is most dense, the probability of finding the electron is greatest and vice versa

James Chadwick then discovered the neutron in 1932, which completes the model of the atom we know today