P1 - matter Flashcards
what was the ‘plum pudding model’?
a model of the atom where negative electrons were spread through the positive ‘pudding’ that made up most of the atom
what did JJ Thomson do?
in 1897, he figured out that atoms weren’t solid spheres, his measurement proved the existence of electrons and he came up with the ‘plum pudding model’
what did Ernest Rutherford do?
in 1909, along with Hans Geiger and Ernest Marsden, Rutherford conducted the gold foil experiment
what did the gold foil experiment involve?
firing positively charged alpha particles at an extremely thin sheet of gold
what was expected to be the result of the gold foil experiment?
from the plum pudding model, they expected the particles to pass straight through the gold sheet or only be slightly deflected
what actually happened in the gold foil experiment?
although most of the particles did go straight through the sheet, some were deflected more than they had expected, and a few were deflected back the way they had come- which the plum pudding model couldn’t explain
what can be concluded from a small number bouncing straight back at the detector?
the mass of an atom is mostly concentrated in the centre in a dense nucleus
what can be concluded from some of the particles being deflected at large angles?
the centre mass is positively charged and repels the alpha particles when they pass nearby
what can be concluded from most particles passing straight through the gold foil?
most of the atom is made of empty space
what was the result of the gold foil experiment?
Rutherford came up with the theory of the nuclear atom to explain his new evidence
what did the model of the nuclear atom show?
Rutherfords model of a nuclear atom showed that most of the mass of an atom is concentrated in tiny, positively charged nucleus at the centre, surrounded by a ‘cloud’ of negative electrons (with most of the atom being empty space)
what made Rutherford’s atomic model impossible?
scientists realised that electrons in a ‘cloud’ around the nucleus of an atom would be attracted to the nucleus, which would cause the atom to collapse
what did Niels Bohr propose to overcome the issue of the collapsing atom?
he proposed a model where the electrons are in shells; he suggested that electrons can only exist in these shells (or fixed orbits), and not anywhere in between and that each shell has a fixed energy
what is the nuclear radius?
about 1x10^-15m
what is the diameter of an atom?
around 1x10^-10m
what is formed when atoms join together?
molecules
what is the equation for density?
density = mass / volume
what are the units for density?
kg/m^3
how do you measure the density of irregular objects?
use a displacement can
what are the rays given out by hot metals called?
cathode rays
what fraction of the mass of a hydrogen particle are the particles in a cathode ray?
1/1000
in the crushing can demo, why does the can get crushed?
- when the can is heated, the gas expands
- the gas that has expanded leaves the can and so few particles remain
- as the can is put in water, it is sealed and so the gas suddenly cools down
- the cool gas’ particles move slowly so exert little pressure on the inside of the can
- the inside of the can’s pressure is now very low in comparison to the air pressure, so the can is crushed
what are the equations for Boyle’s Law?
P is proportional to 1/V
PV = constant
P1V1 = P2V2
how does Boyle’s Law say pressure and volume are related?
pressure is inversely proportional to volume
pressure is directly proportional to the inverse of volume
