physics p1 - matter (copy)

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

• 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 as the nucleus was positive, repelling other positive charges

whats was bohrs model of the atom

• 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.

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/m³) = mass (kg)/ volume (m³)

p = m/v

describe the particle arrangement for a solid

• tightly packed in a regular arrangement

• particles can only vibrate on the spot

describe tha particle arrangement of a liquid

• close together but irregular arrangement

• can flow past each other

describe the particle arrangement of a gas

• separated with no regular arrangement

• particles can move freely

whats the order (most to least) of density for the states of matter

most dense : solid

liquid

least dense : gas

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 5 main ways a substance can change state

1. melt

2. freeze

3. evaporate

4. condense

5. sublimate

whats sublimation

when a substance transitions from a solid straight into a gas without transitioning into a liquid in between

using the particle model, how does condensation occur

• in gases the particles have enough energy to overcome the forces between them so spread out randomly

• when the temperature is lowered , they will no longer have the energy to overcome these attractive forces so the particles will move closer together and condense into a liquid

using the particle model, how does melting occur

• in solids, strong attractive forces hold the particles in place so they can only vibrate

• as the substance is heated the particles gain energy and vibrate more quickly

• eventually the particles have so much energy they overcome the forces holding them together and it melts into a solid to a liquid

using the particle model how does boiling occur

• as heat is applied to a liquid the particles gain kinetic energy and move faster

• with enough energy, the forces of attraction between the particles will break

• at this point the liquid boils into a gas

how is a change of state different to a chemical change

• in a change of state the material can return to having its previous properties if the change is reversed

• in a chemical change, its irreversible

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

no as 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 state, 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. (spacing between the particles changes)

• 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 irregular 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 units of density

kg/m³ or g/cm³

how do you convert from g/cm³ into kg/cm³

• multiply the g/cm³ value by 1000

• e.g. 0.525 g/cm³ = 525 kg/cm³

whats internal energy

the total energy stored by the particles making up a substance or system (kinetic energy + potential energy)

whats temperature

the measure of the average internal energy of a substance

how do you increase the kinetic energy of particles in a substance

• heating the particles transfers energy to kinetic energy store which increases their internal energy

• is measured by an increase in temperature

the more _______ _________ a substance has, the higher its ____________ will be

the more internal energy a substance has, the higher its temperature will be

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

∆E = m x c x ∆T

change in Energy = mass x specific heat capacity x temp joules (J) = (Kg) x (J/Kg) x (°C)

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

E = m x L

energy (J) = mass (kg) x specific latent heat (J/kg)

when a substance is melting or boiling, why dosnt the temperature change until the substance has turned into a liquid or a gas

• the energy is used for breaking bonds between the particles rather than raising the temperature

• shown by the flat spots on the heating graph

what are the 2 types of specific latent heat

• Specific latent heat of vaporisation

• Specific latent heat of fusion

whats specific latent heat of vaporisation

energy change when a substance changes between a liquid + gas

whats specific latent heat of fusion

energy change when a substance changed between a solid + liquid

when cooling a substance, what would the specific latent heat of vaporisation/fusion be

the amount of energy released, rather than required at each stage

whats pressure

a measure of the force per unit area

whats the equation for pressure

p = F/A

pressure = force/ area

what are the units for pressure

pascals (Pa)

how do gas particles trapped in a container behave

they move about randomly travelling in straight lines until they collide with another particle or a wall at which point they will bounce off

how does a gas inside a container exert pressure on the container

• the particles of the gas are moving randomly and collide with the walls of the container

• this exerts a pressure on the container wall

how does decreasing the volume of a container affect the pressure of a gas

• will increase the pressure

• decreasing volume of the container whilst keeping number of gas particles the same will increase the concentration

• there will be a smaller distance between the walls

• these both increase the collisions between the particles and the container meaning more force will be exerted on a smaller area of the container resulting in higher pressure

how does increasing the temperature of a gas in a fixed container will affect the pressure

• higher temperatures mean the particles have more kinetic energy

• means they will collide with the walls more frequently and with more force so the pressure will increase

how does increasing the concentration of gas in a flexible container (like a balloon) will affect the volume

• a higher concentration of particles means more particles in the same volume

• extra particles will collide with walls of the container pushing it outwards increasing the volume

whats the relationship between the pressure and volume of a gas (assuming temperature is kept contant)

• when at a constant temperature, the pressure and a volume of a gas are inversely proportional

• e.g. if you decrease the volume of a container, then the pressure will increase