The Atom Flashcards
How did Rutherford and Marsden prove the plum pudding model of atoms was false
they fired a beam of alpha particles (positively charged) at thin gold foil.
most of the alpha particles went straight through it the odd one came straight back at them.
this means most of the atom was made up of space and most of the mass of the atom was concentrated in the centre in a tiny nucleus which has a positive change as it repelled the alpha particles
what is the nuclear model of the atom today that rutherford and mardsen discovered
- nucleus- tiny , makes up most of the mass of the atom. contains protons and neutrons. so has an overall positive charge
- atom is mostly empty space
- electrons- whizz around energy shells around nucleus very fast. this give the atoms overall size
radius of the atoms nucleus is 10,000 times smaller than the radius of the atom
what are the relative masses and charges for each particle
proton= +1, relative mass of 1
Neutron= no charge, relative mass of 1
electron= -1, relative mass of 1/2000
explain the charge in an atom
atoms have no overall charge
charge on an electron is the same as a proton but opposite. so they balance eachother out and form a neutral atom.
if some electrons are added or removed the atom becomes a charged particle which is an ion
what did Rutherford Scattering think the atom looked like
in 5th centry Democritus said atoms were identical lumps that made up everything
in 1804 John dalton said each element was made from a different type of atom
100 years later JJ thomson discovered electrons could be removed from atoms. So atoms could be broken up.
This led to the plum pudding which thought atoms was a circle of positive charge with negative electrons stuck in them like a plum pudding
what is an isotope
isotopes are atoms with the same number of proton but a different number of neutrons.
so they have the same atomic number but different mass numbers
eg Carbon-12 and Carbon-14
most elements have different isotopes but there’s usually one or two stable ones. The other isotopes tend to be radioactive
what is a radioactive substance
radioactive substances decay into other elements and give out radiation from the nuclei of their atom- no matter what is done to them.
this process is random; you can’t predict when an unstable nuclei will decay/make one decay.
so it’s completely unaffected by physical conditions like temperature of chemical bonding
there is 3 types of radiation: alpha, beta or gamma
what is background radiation
background radiation is radiation that’s present at all times all around us wherever you go
where does background radiation come from
1) naturally occurring unstable isotopes which are all around us
2) space which are known as cosmic rays (these come mostly from the sun)
3) man made sources eg fall out from nuclear weapon tests, or nuclear accidents (Chernobyl) or dumped nuclear waste
explain alpha particles
1) alpha particle has two neutrons and two protons like a helium nucleus
2) they are big, heavy and slow moving
3) so they don’t penetrate very far into materials and are stopped quickly, even if travelling through air
4) due to their size they are strongly ionising which means they bash into lots of atoms and knock electrons off them before they slow down - this creates lots of atoms
explain what beta particles are
- they are electrons so are small and fast moving
- they particles are in between alpha and gamma.
- they penetrate moderately into materials before colliding, have a long range in air and are moderately ionising
- for ever beta particle emitted, a neutron turns into a proton in the nucleus
NEED TO KNOW HOW TO BALANCE NUCLEAR EQUATIONS
LEARN DAT
What are gamma rays
Very short electromagnetic waves
1) opposite of alpha particles
2) penetrate far into materials without being stopped and pass straight through the air
3) are weakly ionising because they pass through rather than collide with atoms. eventually they hit something and do damage
4) gamma rats have no mass or charge
what does the damage caused by radiation depend on
the damage you are likely to suffer depends on the radiation dose
1) the higher the radiation dose, the more at risk you are of developing cancer
2) radiation dose depends on the type and amazing of radiation you’ve been exposed to
how does radiation dose depend on your occupation
1) nuclear industry workers and uranium miners.
exposed to 10x normal amount of radiation. wear protective clothing to stop them from touching or inhaling radioactive material. they monitor radiation doses with special radiation badges and regular check ups
2) radiographers
work in hospitals using ionising radiation so have high exposure. they wear lead aprons and stand being lead screens to protect them from prolonged exposure to radiation
3) Underground workers eg miners
the rocks pose a risk to them
