Section 1 – Particles Notes
10/9/24
Atomic Structure
Thermionic emission – process by which electrons are given off a piece of
metal when heated up.
Magnetic and electric fields cause electrons to change directions.
When electrons go right, conventional current goes left.
Magnetic field makes electrons go up; electric field makes it go down.
By balancing forces on electrons from electric and magnetic fields,
Thomson could work out the ratio of the electron’s electric charge to its
mass.
Charge to mass ratio.
Electric charge : e=-1.6x10-19 C
Mass : me=9.109x10-31 kg
C:m=e/me = -1.76x1011 Ckg-1
e/m is specific charge
mp = 1.67x10-27 kg
e/mp = 9.6x107 Ckg-1
11/9/24
Discovery of the neutron
Specific = per unit mass
,An individual atom is about 10-10m across
Overall charge = 0
Electrons can be removed to make a positive ion or added to make a
negative ion.
The electrons exist in fixed shells well outside the nucleus.
Nuclear forces
The protons inside a nucleus repel each other due to electric charges.
This would cause the nuclei to fall apart.
To hold nuclei together requires an additional force.
The force is known as the strong nuclear force.
, It acts between protons and neutrons, neutrons and neutrons, protons
and neutrons.
Repulsive up to 0.5fm, attractive from 0.5-3fm, strongest at 1.5fm.
It is an attractive force for distance up to 3 fm (3x10 -15m).
Diameter of nucleus is of the order of 10-15m (fm).
A
Z
A is the nucleon number
- The number of nucleons (protons and neutrons) in nucleus
- Also called atomic number
Z is the proton number
- Number of protons in nucleus
- Also called atomic number
- Determines which element it is
Radioactivity
Result of an unstable nucleus becoming more stable.
10/9/24
Atomic Structure
Thermionic emission – process by which electrons are given off a piece of
metal when heated up.
Magnetic and electric fields cause electrons to change directions.
When electrons go right, conventional current goes left.
Magnetic field makes electrons go up; electric field makes it go down.
By balancing forces on electrons from electric and magnetic fields,
Thomson could work out the ratio of the electron’s electric charge to its
mass.
Charge to mass ratio.
Electric charge : e=-1.6x10-19 C
Mass : me=9.109x10-31 kg
C:m=e/me = -1.76x1011 Ckg-1
e/m is specific charge
mp = 1.67x10-27 kg
e/mp = 9.6x107 Ckg-1
11/9/24
Discovery of the neutron
Specific = per unit mass
,An individual atom is about 10-10m across
Overall charge = 0
Electrons can be removed to make a positive ion or added to make a
negative ion.
The electrons exist in fixed shells well outside the nucleus.
Nuclear forces
The protons inside a nucleus repel each other due to electric charges.
This would cause the nuclei to fall apart.
To hold nuclei together requires an additional force.
The force is known as the strong nuclear force.
, It acts between protons and neutrons, neutrons and neutrons, protons
and neutrons.
Repulsive up to 0.5fm, attractive from 0.5-3fm, strongest at 1.5fm.
It is an attractive force for distance up to 3 fm (3x10 -15m).
Diameter of nucleus is of the order of 10-15m (fm).
A
Z
A is the nucleon number
- The number of nucleons (protons and neutrons) in nucleus
- Also called atomic number
Z is the proton number
- Number of protons in nucleus
- Also called atomic number
- Determines which element it is
Radioactivity
Result of an unstable nucleus becoming more stable.
