Flashcards in Topic four - atomic structure Deck (10):
what was the first model of an atom
in 1804, John Dalton agreed with democritus that matter was made up of tiny spheres that couldn't be broken up, but he reckoned that each element was made up of a different type of atom
what is the plum pudding model
thought up by J. J. Thomson suggested atoms were spheres of positive charge with tiny negative electrons stuck in them.
who was it who corrected the plum pudding model, how did he come to his conclusion, and what was his model of an atom
in 1909, Ernest Rutherford did an experiment in which he fired an alpha particle beam at thin gold foil, called the alpha scattering experiment. most of the alpha particles passed straight through. however some were deflected more than expected, and some were even deflected back to where they came. this disproved the plum pudding model. they therefore found that most of the mass was concentrated in the centre in a tiny nucleus which must have had a positive charge, since it repelled the positive alpha particle. they also realised that most of it was empty space. they also found that smaller lighter negatively charged particles must have been in the area around it.
what is the definition of an isotope
isotopes of an element are atoms with the same number of protons but a different amount of neutrons.
what are the three different types of radiation
alpha particles are positively charged helium nuclei, which is usually emitted from the nucleus of a high mass radioactive atom. they don't penetrate very far (i.e. the dead skin cells on the human skin, or a few cm of air) but they are very strongly ionising.
beta particles are electrons or anti-electrons (positrons). they have virtually no mass and a charge or either -1 or +1. they can travel a few metres in air and are stopped by a sheet (5mm) of aluminium. for every negative beta particle, a neutron turns into a proton and the other way round for a positron.
gamma rays are electromagnetic waves with a very short wavelength. they have an infinite range in anything but the likelyhood of it travelling a certain distance through lead decreases with distance.
in what form do you write radioactive decay equations
atom before decay => atom after decay + radiation emitted
remember to keep the total mass, the charge and the atomic numbers the same on both sides.
what is the piece of machinery used to find the radiation in an area
a Geiger-Muller tube and counter
what is the definition of half life
the half life is the time taken for the number of radioactive nuclei in an isotope to halve
give an example of a medical use of radioactive injection.
to find whether the thyroid gland is functioning properly, iodine 123 is taken which is then absorbed by the thyroid and is radioactive to see whether it is functioning properly using external detectors.