Atomic Structure Flashcards
History of the atom
Dalton agreed that matter was made up of tiny spheres but he thought each element was a different type of atom
Thomson discovered electrons. He suggested that atoms were spheres of positive charge with tiny negative electrons stuck in them. This is the plum pudding model.
Rutherford fired a beam of alpha participles at thin gold foil. This was the alpha scattering experiment. They were expected to pass through but some deflected hugely or back the way they came which could not be explained by the plum pudding model. This made them realise that most of the atom was empty space. This was the first nuclear model with positive nucleus surrounded by a cloud of negative electrons.
Developing the current atom model
Bohr said electrons orbited the nucleus at certain distances this developed shells
Chadwick proved the neutron
Alpha particle properties
Helium nuclei
Poor penetrating
Can travel a few cm in air
Absorbed by sheet of paper
Strongly ionising due to size
Beta particle properties
High speed electrons
Moderately ionising
Penetrate moderately
Can travel a few m in air Absorbed by a sheet of aluminium
For every beta particle emitted a neutron in the nucleus has turned into a proton
Gamma particles
Em waves with a short wavelength
Great penetration
Travel long distances in air
Weak ionising as they tend to pass through rather than collide with atoms
Absorbed by thick lead or metres of concrete
Alpha decay
Decreases the charge and mass of the nucleus. This is because they are made of 2 protons and neutrons so when emitted the atomic number reduces by 2 and the mass number by 4.
Alpha is helium nucleus so symbol 4 2 a
Beta decay
Increases the charge of the nucleus. This is because when it occurs a neutron turns into a proton and releases a fast moving electron.
Beta is 0 -1 B
Nuclear equations
Total mass and atomic numbers must be equal on both sides
Atom before decay = atom after decay + radiation emitted
Half life
The time taken for the number of radioactive nuclei in an isotope to halve. It’s used to find the rate radioactive sources decay.
Long means activity falls slower
To calculate you:
Find the activity after each half life. You do this by dividing the previous activity by 2
Now divide the final activity by the initial activity and multiply by 100 to make it a percentage
Uses and risk of radiation
Uses : medical tracers , radiotherapy
Risks : tissue damage if radiation enters living cells , lower doses may cause cancer as the cells causes minor damage to cells giving rise to mutant cells , high doses cause radiation sickness as cells are killed completely
Irradiation and contamination
Irradiation is exposure to radiation. Objects near a radioactive source are irradiated by it but this does not make it radioactive
Contamination is radioactive particles getting onto objects.
Outside body beta and gamma are the most dangerous as they can penetrate skin.
Inside body alpha is the most dangerous as all their damage is in a localised area.
Nuclear fission
Splitting of a large , unstable nucleus
When the atom splits it forms two new lighter elements that are similar sized. Two or three neutrons are released during fission and if these neutrons are slow enough to be absorbed by another nucleus more fission can occur. This is a chain reaction. Uncontrolled chain reactions are how nuclear weapons work as lots of energy is released.
Nuclear fusion
Joining small nuclei. Yep smaller light nuclei collide at high speed and fuse together.
Describe the process of nuclear fission
A neutron is absorbed by a large nucleus. The nucleus splits into two smaller nuclei. Releasing energy and two or three neutrons
Describe the process of nuclear fusion
Two small , light nuclei collide at high speed and join together. The male one heavier nucleus releasing energy.
What fuel is used at nuclear power stations
Uranium or plutonium
Nuclear power vs shale gas
Nuclear power does not :
Emitted carbon dioxide
Cause global warming
Cause earthquakes
Nuclear power does:
Release more energy per Kg of fuel
Describe the ideal properties of a radioactive source for medical diagnosis
Weak ionising and short half life as it causes less damage to cells/organs/tissue
Strong penetration so it can be detected outside the body this emits gamma
Gamma decay
0 0 y
A gamma ray is emitted from an unstable nucleus. Makes the nucleus less energetic but does not change its structure
