particle model of matter - states of matter Flashcards
properties of a solid
- particles are very close together
- arranged in a regular pattern
- particles in a solid vibrate but do not move from place to place
- high density
properties of a liquid
- particles close together
- not arranged in a regular pattern
- particles can move around each other
properties of a gas
- particles very far apart
- move very rapidly
- not arranged in any pattern
Describe Rutherford’s alpha particle experiment
Most alpha particles passed straight through the foil.
This suggested that most of the atom is made up of empty space.
However, some particles bounced back towards the source.
The large deflections suggested that some positively charged mass in the atom was repelling the particles.
This led to the model of the atom with negatively charged electrons orbiting a positively charged nucleus.
Describe JJ Thomson’s plum pudding discovery
In 1897, an English physicist called J. J. Thomson discovered electrons.
He modelled the atom as a ‘plum pudding’ - a ball of positive charge (dough), with negatively charged electrons (currants) mixed in with the ‘dough’.
discovery of protons
In 1909, Ernest Rutherford discovered that alpha particles could bounce back off atoms.
He concluded that an atom’s mass is concentrated in the atom’s centre. This was called the “nucleus” and it contained positively charged particles called protons
what is density
The density of a material tells us the mass for a given volume
density equation
density = mass / volume
why do solids usually have a high density
because their particles are packed closely together, solids have a lot of mass for their volume
why do liquids usually have a high density
because their particles are packed fairly closely together
why do gases have a low density
because the particles are far apart, so gases only have a small mass for their volume
in terms of density, why would an object float
because the objects density is less then the density of the fluid
properties of change of state reaction
- reversible reaction
- physical change
- mass is conserved
when does a liquid boil
when the particles have enough energy to completely escape the forces between them
describe melting ( solid to liquid )
If we heat a solid, the solid particles vibrate more energetically, as we increase the internal energy, until they have enough energy to overcome the forces between them. This is when the solid melts (becomes a liquid).
describe condensation - gas to liquid
When the temperature of a gas decreases to the boiling point, the strength of the forces between particles increases and the particles condense to become a liquid.
- this is because the internal energy is reduced
describe freezing - liquid to solid
When the temperature of a liquid decreases to the melting point, the strength of the forces between particles increases and the liquid solidifies to become a solid.
Describe boiling - liquid to gas
If we heat a liquid, the liquid particles move more energetically until they have enough energy to escape completely from the forces between them. The particles become a gas and move completely freely.
what is density measured in
kg/m^3
what is the particle model used for
the different states of matter
- differences in density.
why are changes of state physical and not chemical changes
because the material recovers its original properties if the
change is reversed
Why is polystyrene low density?
Because polystyrene has a very open structure and is full of air spaces. It has a small mass for its volume
what is the process of solid to gas called
sublimation
properties of changing state reactions
- mass is conserved
- physical changes, if we reverse the change then the material recovers its original properties
what is evaporation
- when a liquid turns into a gas but only on the surface of the liquid
- meaning that only particles on the surface have enough energy to turn into a gas
