- Created by: Beth
- Created on: 24-05-11 17:14
Atomic Structure - How the structure of the atom w
The Rutherford Scattering: This is basically when Ernest Rutherford fired alpha particles at thin gold foil. Most of the particles went straight through but one or two came straight back to them.
From these results, Rutherford deduced that most of the mass of the atom was in the nucleus with a positive charge. The rest of the atom is just empty space.
The Nuclear Model:
A tiny nucleus makes up most of the mass of the atom. It contains protons (positive), and neutrons (neutral). This means that the atom has an overall positive charge.
The rest of the atom is empty space with electrons (negative) flying around the nucleus really fast. They give the atom its overall size.
Atomic Structure: Isotopes and Useful Equations.
The number of protons is the same as the number of electrons in a neutral atom.
Mass number = total number of protons + total number of neutrons.
atomic number = number of protons.
If an atom gains or loses electrons it becomes charged and is called an ion.
Isotopes are atoms which have the same number of protons but a different number of neutrons.
Nuclear Physics-Nuclear Particles.
Alpha Particles: Helium nuclei which are big, heavy and slow moving. They consequently are stopped quickly. They are strongly ionising .
Alpha Particles contain; 2 protons and 2 neutrons. Mass of 4 (top), charge 2(bottom).
When an unstable nucleus emitts an alpha particle, the atomic number(bottom) goes down by 2 and the mass number goes down by 4 (top)
Beta Particles: Electrons. Quite fast and small. Penetrate moderately and ionise moderatley.
Emitted by a nucleus which has too many neutrons compared to protons. A neutron changes into a proton and a beta particle.
When this happens, its atomic number increases by 1 and its mass number stays the same.
Nuclear Physics-Nuclear Particles.
Gamma Particles: Very short electromagnetic waves. Penetrate a long way away. Weakly ionising.
After emitting either an alpha or gamma particle, a nucleus sometimes has some extra energy to get rid of, so it emitts a gamma ray.
Gamma emissions never change the atomic number or mass number.
Nuclear Physics - Nuclear Fission
Nuclear fission is the splitting up of a big atomic nuclei.
In a nuclear reactor, a controlled chain reaction takes place; an atomic nuclei splits up and releases heat energy.
Chain Reactions: A slow moving neutron that has been absorbed by a uranium or plutonium nucleus, can cause the nucleus to split. Every time it splits, it spits out two or three neutrons. These may then hit another nucleus, meaning more nucleus' may split, causing a chain reaction.
Each nucleus splitting gives out a lot of energy.
Nuclear Physics - Nuclear Fusion
Nuclear Fusion is the joining of small atomic nuclei. Two light nuclei can combine to create a larger nucleus.
Fusion releases a lot of energy, all the energy released in the stars come from fusion.
Fusion doesnt leave behind radioactive waste.
But it can only happen at high temperatures, about 10 000 000 degrees.
Not many fusion reactors are in use, because it is hard to generate that high a temperature.
Nuclear Physics - Background Radiation
Can come from many sources including : unstable isotopes in the air/food/building materials, radiation from space (cosmic rays from the Sun), and nuclear explosions/dumped nuclear waste.
The level of radiation depends on where you are: high altitudes and underground = increase in radiation exposure.
Radon gas is scientifically controversial: varies in all households depending on the type of rock the house is built on. Carries a risk of lung cancer, but other scientists disagree.