Shells
Shells represent amounts of energy.
Electrons
Electrons can absorb specific amounts of energy to move between shells. If they lose energy they move to shells closer to the nucleus. If they gain energy they move to shells further away from the nucleus.
Proton - relative charge
+1
Proton - relative mass
1
Proton - where
In the nucleus
Neutron - relative charge
0
Neutron - relative mass
1
Neutron - where
In the nucleus
Electron - relative charge
- 1
Electron - relative mass
1/2000
Electron - where
Orbiting the nucleus
Atomic number
number of protons
Mass number
number of nucleons - protons+neutrons
computer -------> Isotopes
Isotopes are forms of an element that have the same number of protons but different numbers of neutrons.
Decay
Unstable -------------> Stable + ionising radiation
nuclei DECAY nuclei
Activity
- Number of decays per second
- Measured in becquerels (Bq)
Activity equation
Activity = Number of decays
------------------------------
Time taken
Kilo
- K
- 1000
- 10/3
Centi
- C
- 0.01
- 10/-2
milli
- m
- 0.001
- 10/-3
micro
-
- 0.000001
-10/-6
nano
- n
- 0.0000001
- 10/-9
pico
- p
- 0.000000000001
- 10/-12
Giga
- G
- 1000000000
- 10/9
Mega
- M
- 1000000
- 10/6
Radioactive decay
- Random
- Can't control it
Half life
- An amount of time it takes for the activity/number of unstable nuclei to half.
Alpha
- Travels up to a few centimetres.
- Alpha particles are attracted to negatives.
- Unable to pass through paper.
Beta
- Travels up to about one metre.
- Beta particles are electrons, they don't interact as strongly with atoms as alpha particles and are lighter.
- Beta particles are attracted to positives.
Gamma
- Gamma particles have a long range.
- Can penetrate even thick lead.
- Being far away is the best protection.
- Gamma rays ionise one atom or molecule as they lose energy after the first one.
Contamination
- Absorbed a radioactive material.
Irradiation
- Absorbed ionising radiation.
atom
An atom has a small, positively-charged nucleus surrounded by orbiting negatively-charged electrons.
Atoms are very small and have a radius of about 1 × 10-10 metres.
The electrons are arranged at different distances from the nucleus (different en.rgy levels).
The radius of a nucleus is less than 1/10 000 of the radius of an atom.
Most of the mass of an atom is concentrated in the nucleus.
In what environment would the relative mass of an atom change?
Mass is constant in all environments
What is the overall charge of the nucleus of an atom?
positive
Rutherford's experiment
- Most alpha particles travelled right through the foil
- This suggested that most of an atom is empty space.
- However, some particles bounced back towards the source
Rutherford's conclusions
- The large deflections suggested that some positively charged mass in the atom was repelling the particles.
- This led to the model of the atom with negatively charged electrons orbiting a positively charged nucleus.
Why would the alpha particles be deflected by a smaller angle if the thin metal foil was made of a lighter element?
- The nuclei of lighter elements contain fewer protons. This means they have a lower charge. Each alpha particle will, therefore, experience a smaller electric force acting on it and so deflect by a smaller angle.