Studied by 9 people
plum pudding model
discovered electrons which are dotted around inside spheres of positive charge
atoms have a central, positively charged nucleus with most of the mass
nucleus surrounded by cloud of negative electrons so most of atom is empty space
aimed beams of positively charged alpha particles at very thin gold foil.
According to the plum pudding model, these particles should have passed straight through. However, many of them changed direction instead.
this meant it had to have a small positively charged nucleus
a problem with Rutherford's model - the electrons would eventually fall into the nucleus because they are negatively charged and so attracted to the positive nucleus.
Niels Bohr improved Rutherford's model. Using mathematical ideas, he showed that electrons occupy shells around the nucleus.
what is an atom
a positively charged nucleus surrounded by negatively charged electrons, with the nucleus size being much smaller than that of the atom and with the most mass in the nucleus
a measure of ‘ compactness’
Mass per unit volume
yes as when a substance changes state its volume changes as the partciles are closer together in a solid and further away in a liquid + gas.
denisty = mass/ volume so density must change too
solids are most dense and gasses are least
find out mass by weighing it
for volume do length x width x height
mass / volume
how do you find the density of an object
find out mass by weighing it
for volume use a eurika beaker
mass / volume
fill eurika beaker so water level is just under the spout
place measuring cylinder under spout and put object in water
the volume of water collected in the measuring cyclinder is the volume of the object
strong forces of attraction hold particles close together in a fixed , regular arrangement
only vibrate as not much energy in kinetic energy stores
why is a solid denser than gas
because the particles are tightly packed in a regular structure whereas in a gas the particles are spread out
weaker forces of attraction between particles
particles can flow over each other to form irregular arrangement
more energy in kinetic energy stores
almost no forces of attraction between particles and are free to move
particles travel in random directions at high speeds
have lots of energy in kinetic energy stores
how does a liquid become a gas
adding more heat energy breaks the bonds between the atoms completely
whats it called when a solid turns into a liquid
melting
whats it called when a liquid turns into a solid
freezing
whats it called when a liquid turns into a gas
evaporating
whats it called when a gas turns into a liquid
condensing
whats it called when a gas turns into a solid/ solid turns into a gas
sublimating
what 2 things can heating a substance do
raise its temperature
change the state of the substance
