P3 Partical Model of Matter/P4 Atomic Structure Random Revision (pages 191-199)

Question 1

Describe the motion of particles in a gas.

Answer 1

Particles are constantly moving with random directions and speeds.

Question 2

How is the speed of a gas’s particles related to the pressure that the gas exerts on its container?

Answer 2

E.g. the higher the speed of its particles, the higher the pressure.

Question 3

State the missing variable in the equation below.
Mass
Density = _____________
?

Answer 3

Volume

Question 4

Which state of matter is typically the densest?

Answer 4

Solid

Question 5

Describe how you could find the density of a regular solid object, such as a cuboid.

Answer 5

E.g. measure the mass of the object using a mass balance. Measure the dimensions of the object using an appropriate piece of equipment (e.g. a ruler) and calculate the volume of the object using the correct formula for the object’s shape. Divide the mass of the object by its volume to find its density.

Question 6

Describe how you could use a eureka can to find the volume of a solid object.

Answer 6

Fill the eureka can to just below the spout with water. Place a measuring cylinder under the spout. Place the object into the eureka can. This will push some water out through the spout. Record the volume of water collected in the measuring cylinder. This is the volume of the object.

Question 7

The internal energy of a substance is the total energy that its particles have in which energy stores?

Answer 7

Kinetic energy stores and potential energy stores.

Question 8

True or false? A change of state is a physical change. Explain your answer.

Answer 8

True. When a substance undergoes a change of state, it doesn’t change into a new substance (like in a chemical change). Instead, the particles of the substance just arrange themselves differently, and will recover their original properties if the change is reversed (a physical change).

Question 9

Why is mass conserved when a substance changes state?

Answer 9

Because a change of state just means changing the arrangement of the particles in the substance — the number of particles stays the same, so the mass of the substance doesn’t change.

Question 10

Name one change of state that can occur when a substance is cooled

Answer 10

Any one from:

condensing

freezing

Question 11

True or false? When a substance undergoes a change of state, the temperature of the substance changes but its internal energy stays the same.

Answer 11

False. (The temperature of the substance stays the same but its internal energy changes.)

Question 12

The specific latent heat of fusion gives the energy change when 1kg of a substance undergoes which two changes of state?

Answer 12

Melting and freezing

Question 13

What is defined as ‘the energy required to turn 1kg of a substance, at a constant temperature, from a liquid state to a gaseous state’?

Answer 13

The specific latent heat of vaporisation (of the substance).

Question 14

Describe both the plum pudding model and the current nuclear model of the atom.

Answer 14

In the plum pudding model, atoms are spheres of positive charge with tiny negative electrons stuck in them. In the current nuclear model, atoms are made up of a central, positively charged nucleus with negatively charged electrons orbiting around it. This nucleus is made up of protons and neutrons.

Question 15

Describe what happens when a beam of alpha particles is fired at a thin sheet of gold.

Answer 15

Most of the particles go straight through the sheet, unaffected. Some of the particles are deflected. A tiny number of the particles are deflected back the way they came.

Question 16

What is the approximate size of an atom’s radius inmetres?

Answer 16

1 × 10−10m

Question 17

Explain why atoms have no overall charge.

Answer 17

Because the number of electrons (negative charges) in an atom is equal to the number of protons (positive charges) in the nucleus.

Question 18

What is meant by the ‘atomic number’ of an atom?

Answer 18

The number of protons in the nucleus of that atom.

Question 19

All atoms can be represented with the notation shown below. What property of an atom is labelledZ?

A
X
Z

Answer 19

Its atomic number

Question 20

Atoms with the same number of protons but a different number of neutrons to other atoms of that element are called what?

Answer 20

Isotopes

Question 21

What process do unstable nuclei undergo in order to become more stable?

Answer 21

Radioactive decay

Question 22

State the three types of ionising nuclear radiation. Briefly describe what each one is made up of.

Answer 22

Alpha particles — particles consisting of two neutrons and two protons.

Beta particles — fast‑moving electrons.

Gamma rays — waves of electromagnetic radiation.

Question 23

Which type of ionising radiation can only travel a few cm in air?

Answer 23

Alpha particles

Question 24

Which types of ionising radiation aren’t able to penetrate through a sheet of aluminium?

Answer 24

Alpha particles and beta particles

Question 25

How do the atomic and mass numbers of an atom change when its nucleus emits an alpha particle?

Answer 25

Its atomic number decreases by 2 and its mass number decreases by 4.

Question 26

Why does the atomic number of an atom increase by 1 when the atom undergoes beta decay?

Answer 26

Because during beta decay, a neutron in the nucleus turns into a proton, meaning the nucleus has 1 more proton than before.

Question 27

The activity of a radioactive source is measured in what?

Answer 27

Becquerels (Bq)

Question 28

Define ‘half-life’ in terms of activity

Answer 28

The time taken for the activity of a sample to fall to half of its initial value.

Question 29

Describe how you can determine the half‑life of a source from a graph of its count‑rate over time.

Answer 29

E.g. look at the initial count‑rate (the count‑rate whent= 0). Then find the time when the value of count‑rate is half of this value. This time is the half‑life.

Question 30

What is the term for when unwanted radioactive atoms get onto or into an object?

Answer 30

Contamination

Question 31

When handling radioactive sources, state one safety precaution you could take to lower the risk from irradiation.

Answer 31

Any one from e.g.:

Store radioactive sources in lead‑lined boxes when they’re not being used.

Stand behind barriers that will absorb radiation when using sources.

Question 32

Explain why contamination can be hazardous.

Answer 32

Because contaminating atoms can decay and release radiation which could cause harm.

Question 33

State and explain whether an alpha or gamma source is more dangerous for a person to be irradiated by.

Answer 33

Gamma source. This is because gamma radiation has a longer range, and so more radiation will reach a person from a gamma source than an alpha source at the same distance. Gamma radiation can also penetrate a person’s body and damage their organs, which alpha radiation cannot.