Nuclear and Particle Physics

Period table strucutre

A = Nucleon Number

N = Proton number

X = Symbol

Number of protons = Number of electrons = N

Number of neutrons = A - N

History of the atom

Scattering Experiment

Radiation

Alpha

Beta

Nucleus loses 2 protons and 2 neutrons

Emitted as an alpha particle

Alpha Radiation

Neutron becomes a proton and an electron. The electron is emitted.

Beta Radiation

Observations

Rutherford scattering

Most alpha particles passed through undeflected

Some particles were deflected at small angles

1/10000 were 'back-scattered'

Most of atom must be empty space

Suggests α particles experience a force within atom, but this entity is small

In 'Plum Pudding', back-scattering wasn't expected

Suggests α particles 'collides' with a larger entity within the atom, causing major deflection of α

PLUM PUDDING MODEL REJECTED

Nuclear Model

α particles experiences a repulsive force as they enter the electric field produced by positively charged nucleus as per COULOMB'S LAW

This force increases until it is out of kinetic energy and it is repelled until energy is regained.

Ek --> 0Ek + Max Electric Potential Energy

Elastic Collision, although no contact is maded

Atoms are mostly empty space and most pass at minimal angle.

r _

0

r(subscript 0)

(Closest point it reaches before deflection

Why was gold used?

1) It is ductile so it can be formed into a thin sheet

2) It is heavy - nucleus doesn't move

1. DEMOCRITUS (442 BC)

MODEL: Matter consists of invisible particles called atoms and a void. Model was solid but had different size, shape, mass, position and arrangement

2. DALTON (1803)

MODEL: All elements are composed of atoms, atoms of different elements are different, atoms of different elements combine to form a compound

3. THOMSON(1904)

MODEL: Plum Pudding Model

4. RUTHERFORD (1911)

MODEL: Planetary model, small dense filled centre with positive charges (nucleus), negatively charged electrons surround the centre

5. BOHR (1913)

MODEL: Energy Level Model (Contains dense positive nucleus. Expanded on Rutherford's ideas focusing on electrons)

6. SCHÖDINGER (1926)

Discovered electrons don't move in orbits. Theorises electrons move in waves and have no exact position

7. CHADWICK (1932)

Led to the discovery of neutrons

Property | Electron | Proton | Neutron

Charge | -1e | +1e | 0

Mass |9.11x10^-31|1.67x10^-27|1.67x10^-27

Relative Mass | 0.0005 | 1.0000 | 1.0004

Isotopes

- Same number of protons

- Different number of neutrons

- Same Physical & Chemical Properties

- Some are radioactive --> nuclei is unstable

eV --> J --> kg

ne = n = 1.6x10^-19

m = E/c^2