atomic structure Flashcards
whats the plum pudding model
the plum pudding model showed the atom as a ball of positive charge with electrons stuck in it
whats the alpha scattering experiment
rutherfored fired alpha particles (ox) at a sheet of thin gold foil. he deduced the following most of the alpha particles go through undeflectd this shows that most of the atom is empty space. some deflected by small angles which tells us the atom has a nucleus with a positive charge
some are deflected by large angles. this shows most of the atoms mass is concentrated in nucleus
mass and charge of proton neutron and electron
proton 1 +1
neutron 1 0
electron 1/2000 -1
whats the mass number
number of protons plus neutrons
whats the atomic number
the number of protons in the nucleus
atoms of an element always have the same..
atomic number
whats an ion
atoms are neutral but if some electrons are added or removed the atom becomes a charged particle called an ion
what do the ions still have the same as with the atom
the ions still have the same number of protons and neutrons as usual, but a different number of electrons
whats it called if an atom has had electrons added or removed
ionisation
whats an isotope
different forms of the same element which have the same number of protons but a diff number of neutrons this means they have the same atomic no. but a different mass no.
what are unstable isotopes and what does it mean
the unstable isotopes are radioactive ,which means they decay into another elements and give out radiation
whats radioactive decay
some atomic nuclei are unstable in order for them to become more stable they emit ionising radiation. the process of radioactive decay is random and unpredictable. there r 3 types
whats the 3 types of decay
alpha,beta and gamma
whats alpha decay
an alpha particle (helium nucleus) is emitted from the nucleus. an alpha particle is 2 protons and 2 neutrons. during alpha decay mass no. decreases by 4 , atomic no. by 2 and charge by 2
whats beta decay
when a neutron turns into a proton and an electron. electron leaves the nucleus. after beta decay mass number is unchanged atomic no increases by 1 charge has increased by 1
whats gamma decay
after a nucleus has undergone alpha or beta decau the excess energy in the nucleus is released as a gamma wave. after gamma decays the nucleus has not changed
whats gamma
its a high energy electromagnetic wave
whats activity measured in
becquerels (Bq) 1 Bq - 1 decay per second
whats activity
rate of which a sample decays
half life definition
average time taken for count rate to halve
whats the count rate
when were measuring the radiation emitted from the source we use a GM tube to detect the radiation. the amount detected per second is known as the count rate
for alpha whats the
structure
penetrating ability
range in air
ionising power
uses
2 protons 2 neutrons
paper
2-3cm
most ionising
smoke detector
for beta whats the
structure
penetrating ability
range in air
ionising power
uses
fast moving electron
2-3mm aluminium
1m
less ionising than alpha
monitoring thickness of aluminium foil
for gamme whats the
structure
penetrating ability
range in air
ionising power
uses
electromagnetic waves
thick led/concrete
most penetrating
unlimited
less ionising
detecting leaks
when does irradiation occur
occurs when exposed to radiation from a source
how to reduce risk of irradiation
to reduce the risk we keep sources in lead lined boxes. we also make sure that we keep a safe distance from a source
when does contamination occur
occurs when radioactive material is inhaled or ingested this also means that a person is irradiatedb
whats effects of radiation on living cells
alpha,beta and gamma radiation enter living cells they collide with molecules and cause them to become ionised. this either damagaes or destroys the molecules. this might then cause cells to be killed or DNA to be damaged
effects of low doses
cause minor damage without killing cells. often mutations occurs which may cause cells to divide uncontrollably, causing cancer
effects of high doses
these tend to cause death of a large number of cells, which then causes radiation sickness the extent of the damage done depends upon how much exposure there is to radiation
type of radiation absorbed
what are the medical uses of radiation
tracers - certain isotopes r injected into the body and their progress around the body can be monitored externally by detector. this helps to diagnose medical conditions e.g. cancerous tumours
radiotherapy - gamma radiation can be used to treat cancer by exposing the tumour cells to intense gamma radiation. the radiation must be targeted accurately at the tumour cells to avoid harming the healthy tissue as any damage to healthy tissue will make patient unwell
risk v benefit of radiation in medical use
doctors will consider the risk of treatments vs the benefit to a patients health e.g. imaging using radiation poses a small risk but has a potentially large benefit to the survival of a patient
whats nuclear fission
when an unstable uranium nucleus absorbs a free neutron and splits into 2 roughly equal sized daughter nuclei. lots of energy and 2/3 neutrons are released. the neutrons that are produced can go on t cause further fission events causing a chain reaction
whats the only isotope that can undergo fission
uranium 235 and plutonium 239
wheres the energy released during fission transferred
the energy released during fission is transferred to the kinetic store of the daughter nuclei and the neutrons. In a nuclear power station this energy is then transferred to thermal stores of water which turns to steam which turns a turbine + then turns a generator
definition of fusion and where does it happen naturally
when 2 lighter nuclei join together to form a larger, more stable nucleus. this process releases energy and occurs naturally in stars e.g. sun releases energy
