physics - atomic structure (7.1/7.2/7.3)

Question 1

what is the plum pudding model?

Answer 1

the idea that atoms are spheres of positive charge with tiny negative electrons stuck in them, like fruit in a plum pudding.

Question 2

who discovered the plum pudding model

Answer 2

J J Thomson

Question 3

what is the nuclear model?

Answer 3

the idea that atoms have a very small, positively charged nucleus, consisting of positive protons and neutral neutrons in the centre where most of the mass is concentrated, and shells of negative electrons orbiting the nucleus.

Question 4

what are the relative masses of each subatomic particle

Answer 4

proton-1
neutron-1
electron-1/2000

Question 5

what are the relative charges of each subatomic particle

Answer 5

proton +1
neutron 0
electron -1

Question 6

what is the atomic number

Answer 6

the number of protons in the nucleus of the atom

Question 7

what is the mass number

Answer 7

the number of protons plus the number of neutrons in the nucleus

Question 8

what is an ion

Answer 8

an atom with a positive or negative charge (it loses or gains electrons in order to have a full outer shell)

Question 9

what are isotopes

Answer 9

different forms of the same element, same number of protons and electrons but different number of neutrons (same atomic number but different mass number)

Question 10

what is radioactive decay

Answer 10

when unstable isotopes decay into other elements and give out radiation randomly as they try to become more stable.

Question 11

what is ionising radiation

Answer 11

radiation that knocks electrons off atoms, creating a positive ion

Question 12

give three examples of ionising radiation

Answer 12

alpha, beta and gamma

Question 13

what is alpha decay

Answer 13

when an alpha particle (two protons and two neutrons) is emitted from the nucleus

Question 14

give some general information on alpha particles

Answer 14

they are relatively big, heavy and slow-moving, they have low penetrability (they are stopped quickly), they only travel a few centimetres in air and are absorbed by a sheet of paper, they are very strongly ionising.

Question 15

what is beta decay

Answer 15

a fast-moving electron released by a nucleus (so it has a mass of 1/2000 and a relative charge of -1)

Question 16

how is beta radiation released

Answer 16

a neutron turns into a proton in the nucleus of the atom, increasing the charge by 1 but leaving the mass number unchanged.

Question 17

give some general information on beta particles

Answer 17

they move quite fast and are very small. they are moderately ionising and have moderate penetrability. they have a range in air of a few metres and can be absorbed by a sheet of aluminium (roughly 5mm thick).

Question 18

what is gamma decay

Answer 18

short wavelength EM waves released by the nucleus. Gamma rays have no mass and no charge.

Question 19

give some general information on gamma waves

Answer 19

they have very high penetrability and can pass straight through air. they are weakly ionising as they tend to pass through rather than collide with atoms. they can absorbed by thick sheets of lead or metres of concrete

Question 20

what does it mean if a substance is radioactive

Answer 20

it randomly gives off radiation from the nuclei of its atoms.