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Nuclear and Particle Physics (History of the atom (1. DEMOCRITUS (442 BC) …
Nuclear and Particle Physics
A = Nucleon Number
N = Proton number
X = Symbol
Number of protons = Number of electrons = N
Number of neutrons = A - N
History of the atom
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
Scattering Experiment
Observations
Most alpha particles passed through undeflected
Most of atom must be empty space
Some particles were deflected at small angles
Suggests α particles experience a force within atom, but this entity is small
1/10000 were 'back-scattered'
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
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
Radiation
Alpha
Nucleus loses 2 protons and 2 neutrons
Emitted as an alpha particle
Beta
Neutron becomes a proton and an electron. The electron is emitted.
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
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
