Atomic structure Flashcards
What did Rutherford’s alpha scattering experiment prove?
- Straight through particles = empty space in the atom
- Slightly deflected = the alpha particles hit positively charged particles (protons)
- Directly backwards = positive mass was concentrated in a tiny nucleus
What was Niels Bohr’s discovery
Electrons orbit the nucleus at certain distances called energy levels
What was James Chadwick’s discoveries
Neutrons to explain the imbalance between atomic and mass numbers
Features of a proton
Mass = 1
Charge = +1
Features of a neutron
Mass = 1
Charge = 0
Features of an electron
Mass = 0
Charge = -1
Why does an atom have no overall charge
Protons always equal electrons
How can energy levels move in an atom
Absorbing or losing EM radiation
What is an isotope
An atom with the regular number of protons (same charge) but different amount of neutrons (different mass)
How many isotopes of an element are stable
1 or 2
How do unstable isotopes attempt to become stable
Decay into other elements and give out radiation to try and become stable
What is ionizing radiation
Radiation which knocks electrons off an atom, creatin an ion
Features of an alpha particle
- Helium nucleus (2 protons, 2 neutrons)
- Not very penetrating (stopped by a few cm of air and absorbed by a sheet of paper)
- Strongly ionizing
Features of a beta particle
- Fast moving electron
- Moderately penetrating (can travel a few metres of air, absorbed by a sheet of aluminium)
- For every beta particle emitted, a neutron becomes a proton
Features of a gamma ray
- Waves of electromagnetic radiation
- Very penetrating (absorbed by thick sheets of lead/ concrete)
- Weakly ionizing, as they pass straight through
Nuclear equation for an alpha particle
- 4 from the mass
- -2 from the atomic number
- a helium nucleus
Nuclear equation for a beta particle
- +1 to the atomic number
- a 0 weight, -1 atomic number electron
How is radiation measured
Geiger Muller tube and counter
What is half life
The time taken for the amount of radioactive nuclei in an isotope to halve
What is radioactivity measured in
becquerels
What does a short half life mean
- Activity falls quickly
- Nuclei are very unstable and decay quickly
What does a long half life mean
- Activity falls slowly
- Most nuclei don’t decay for a long time
How is half life shown on a graph
An exponential curve
What is background radiation
Low level that is around us all the time due to the unstable isotopes in objects all around us
Why do cosmic rays from the Sun not affect humans
The Earth’s atmosphere block the radiation
What does irradiated mean?
An object exposed to radiation
3 sources of background radiation
- Sun
- Naturally occurring unstable isotopes
- Human activity
3 ways to avoid irradiation?
- Lead lined boxes
- Standing behind barriers
- Remote controlled arms
2 ways to avoid contamination?
- Gloves
- Tongs
Which radiation types are most dangerous outside the body
Beta and gamma can penetrate skin and damage organs
Which radiation type is most dangerous inside the body
Alpha ionize a very localised area
Difference between irradiation and contamination
Irradiation is being exposed to a radioactive source, contamination is radiation getting inside or onto an object
How can radiation damage the body?
Radiation can enter living cells and ionize atoms and molecules within them and cause mutant cells which divide uncontrollably (cancer)
How are gamma rays used in medicine
- Iodine 123 can detect if the thyroid is taking in iodine as it should
- Gamma rays can be directed carefully at tumours to kill cancer cells without damaging normal cells
Benefits of radiation treatment
- Tracers can detect life threatening illnesses
- Risk of cancer from one is very low
- Cancer can be cleared
Risks of radiation treatment
Side effects
What is fission
Releasing energy from large, unstable nuclei by splitting them into smaller, lighter elements
Explain fission
- A nucleus absorbs a neutron
- The nuclei split to form to similarly sized elements with some energy in their kinetic energy stores
- Two or three nuclei are also released which, if moving slow enough, can be absorbed by another nuclei starting a chain reaction
- Energy not in kinetic energy stores is released in gamma rays
What can fission be used for
Remaining free neutrons and other decay products can heat water to make steam to turn turbines and generators
How is fission controlled
Control rods in nuclear generators can be lowered and raised to absorb neutrons, slow down the reaction and control energy being released
Explain fusion
- Two light nuclei move towards each other at high speed to create a larger, heavier nucleus
- The heavier nucleus does not have as much mass as the two lighter nuclei as some is converted into energy (gamma rays)
3, Lots of energy is released
