ATOMIC STRUCTURE

Question 1

describe the basic structure of an atom

Answer 1

nucleus containing protons and neutrons, around which electrons orbit in fixed energy levels

Question 2

describe the plum pudding model of the atom

Answer 2

sphere of positive charge with negative electrons embedded in it

Question 3

why do all atoms have no overall charge

Answer 3

equal numbers of positive protons and negative electrons

Question 4

how small is the nucleus compared to the whole atom

Answer 4

10 000 times smaller

Question 5

how can an electron move up an energy level

Answer 5

absorb sufficient electromagnetic radiation

Question 6

what is ionisation

Answer 6

process which adds or removes electrons from an atom

Question 7

what is formed if an atom loses an electron

Answer 7

positive ion

Question 8

how does an atom become a negative ion

Answer 8

gains electrons

Question 9

what is the atomic number of an element

Answer 9

number of protons in one atom of the element

Question 10

what is the mass number of an element

Answer 10

number of protons and neutrons

Question 11

which particle do atoms of the same element always have the same number of

Answer 11

protons

Question 12

what are isotopes

Answer 12

atoms of the same element with the same number of protons but a different number of neutrons

Question 13

what were the two main conclusions form the alpha particle scattering experiment

Answer 13

• most of the mass of an atom is concentrated in the nucleus
• nucleus is positively charged

Question 14

what are the three types of nuclear radiation

Answer 14

alpha, beta and gamma

Question 15

what is gamma radiation

Answer 15

electromagnetic radiation from the nucleus

Question 16

what type of nuclear radiation is the most ionising

Answer 16

alpha

Question 17

what is the range in air of alpha, beta and gamma radiation

Answer 17

a few cm, 1m and unlimited

Question 18

which materials stop alpha, beta and gamma radiaiton

Answer 18

sheet of paper, thin aluminium sheet and thick concrete

Question 19

which type of nuclear radiation does not cause a change in the structure of the nucleus when it is emitted

Answer 19

gamma

Question 20

what is radioactive activity

Answer 20

the rate at which a source of unstable nuclei decays

Question 21

what unit is used to measure the activity of a radioactive source

Answer 21

becquerel

Question 22

what is count rate

Answer 22

number of decays each second

Question 23

what is meant by the half life of a radioactive source

Answer 23

time taken for half the unstable nuclei to decay or time taken for the count rate to halve

Question 24

what is irradiation

Answer 24

exposing an object to nuclear radiation

Question 25

what is radioactive contamination

Answer 25

unwanted presence of substances containing radioactive atoms on or in other materials

Question 26

where does background radiation come from

Answer 26

rocks, cosmic rays, nuclear weapons

Question 27

why are gamma emitting sources used for medical tracers and imaging

Answer 27

pass through the body without causing damage to cells

Question 28

what is nuclear fusion

Answer 28

when two light nuclei join to make a heavier one

Question 29

what is nuclear fission

Answer 29

the splitting of a large and unstable nucleus into two smaller nuclei

Question 30

how does nuclear fission occur

Answer 30

an unstable nucleus absorbs a neutron, it splits into two smaller nuclei, and emits two or three neutrons plus gamma rays