physics p1 - matter

ocr gateway combined science higher

What was j.j Thomsons thoery of the atom

* plum pudding model
* discovered electrons which are dotted around inside spheres of positive charge

what was rutherfords theory if the atom

* 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

what experiment did rutherford and marsden conduct

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* 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

whats was bohrs model of the atom

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* a **problem** with Rutherford's model - the **electrons** would eventually f**all 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.

how big is the diameter of an atom

1 x 10 to the power of -10 m

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

what does the nucleus of an atom contain

protons and nutreons ( so positively charged)

what is density

* a measure of ‘ compactness’
* Mass per unit volume

what is the equation for density

denisty (kg/m 3) = mass (kg)/ volume (m2)

when a substance changes state, does the mass change and why

no because the mass of a substance is the mass of its particles and the particles arent changing they’re just being rearranged

when a substance changes shape, does the density change and why

* 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

how do you measure the denisty of a solid cuboid

* 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

how do you use a eurika beaker to find the volume of an object

* 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

what are the characteristics of a solid

* 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

what are the characteristics of a liquid

* weaker forces of attraction between particles
* particles can flow over each other to form irregular arrangement
* more energy in kinetic energy stores

what are the characteristics of a gas

* 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

why do solids melt into liquids

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because as particles vibrate more, some of the forces of attraction between them weaken causing the solid to melt into a liquid

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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

1. raise its temperature

2. change the state of the substance

What's specific heat capacity?

the energy required to raise the temperature of 1kg of a substance by 1 degree

what does a low heat capacity mean

it heats up quickly

what does a high heat capacity mean

it takes longer to get hot

whats the equation for specific heat capacity

Energy = mass x specific heat capacity x temp change

whats specific latent heat

the amount of energy needed to change the state of 1 kg of material without changing its temperature

whats the equation for specific latent heat

energy = mass x specific latent heat

whats the equation for pressure

pressure = force/ area

how does the temperature make the pressure go up

high temperatures mean particles have more heat energy and collide with the sides of the container more

why does decrease in volume make the pressure go up

particles have less room to move meaning they collide with the container more frequently