Atoms and Isotopes

describe the structure of an atom

• nucleus in the centre with shells around

• protons and neutrons in the nucleus

• electrons orbit around the atom in the shells at different distances (radius)

• these shells give the atom the overall size

what are the charges and mass of the particles in an atom

• proton: +1 charge, mass 1

• neutron 0 charge, mass 1

• electron -1 charge, mass 1/1836(2000)

why is an atom neutral

• atoms have the same number of protons and electrons

• charge of proton is +1 and charge of electron is -1

• neutrons have no charge so the charges balance and the atom has no overall charge

how does an atom become a positive ion?

• looses its outer electrons

• has more protons than electrons so has an overall positive charge

what is an isotope?

variants of an atom with the same number of protons but a different number of neutrons (same atomic number - different mass number)

why do isotopes tend to be radioactive?

• the nucleus is unstable and its decays at random, emitting radiation, for example carbon-14 is an unstable isotope or carbon

why is radioactive delay a random process?

• the nuclei is unstable and breaks down randomly

• you can’t say when a nuclei will decay or why

• its decays spontaneously and is unaffected by physical condition eg. temperature or chemical bonding

• when the nucleus decays, one or more types of radiation is emitted

• in this process the nucleus often changes into a new element

what types of radiation are emitted from unstable nuclei?

• alpha particles

• beta minus particles

• gamma rays

• neutron radiation

which types of radiation are ionising?

• alpha

• beta

• gamma rays

what is background radiation?

• there is low level radiation around us all the time

• it is in very small amounts so not harmful

what does background radiation come from?

• unstable nuclei in rocks, also given out as gas

• radiation used in medicine

• cosmic rays - usually from the sun

• living things - plants can absorb radioactive material as they grow - passed on to animals that eat them

• radiation from human activity e.g. fallout from nuclear explosions or waste (usually a tiny proportion of the total background radiation)

how does nuclear radiation cause ionisation

• nuclear radiation bashes into atoms and knocking the electrons off

• atoms are turned into ions - hence ‘ionisation’

• the further the radiation can penetrate before hitting an atom, the less damage it will do, so it is less ionising

what can be used to detect ionising radiation

• Gieger-Muller detector

• Photographic Film

alpha particles - made up of what, what they do, what happens to them

• Alpha particles are made up of 2 protons and 2 neutrons - positively charged helium nuclei

• they don’t penetrate far, being stopped quickly because they are big, heavy and slow moving

• because of their size they are strong ionising - bashing into many atoms and knocking off electrons, creating ions - this happens before they slow down

• positive charge means the particles deflect off of electric and magnetic fields

• MOST IONISING

beta particles - made up of what, what they do, what happens to them

• beta particle is an electron emitted from the nucleus of an atom when a neutron turns into a proton and electron pair

• fast moving and quite small - moderately penetrating

• also moderately ionising - not as strong because of 1- charge vs 2+ charge of alpha

• also deflected by electric and magnetic fields because of the negative charge

• MIDDLE IONISING

gamma rays

• have no mass - energy in electromagnetic waves

• penetrate a long way into materials without being stopped

• weakly ionising as they tend to pass through rather than collide with atoms - although eventually hit something and do damage

• no charge so not deflected by electric or magnetic fields

• gamma emission is always after alpha or beta decay NEVER JUST GAMMA RAYS

• gamma ray emission has no effect on atomic or mass numbers of isotope

• if a nucleus has excess energy, it looses it by emitting a gamma ray

• LEAST IONISING

Alpha emission - nuclear equations

• mass number decreases by 4

• atomic number decreases by 2

Beta emission - nuclear equations

• mass number stays the same

• atomic number increases by 1

Gamma emission - nuclear equations

• mass number stays the same

• atomic number stays the same

Neutron emission - nuclear equations

• mass number decreases by 1

• atomic number stays the same