Atomic Structure

Question 1

Dalton theory of atom

Answer 1

Tiny spheres that could not be divided

Question 2

JJ Thomson theory of atom

Answer 2

• discovered electrons that could be removed from atoms
• plum pudding model - atom is ball of positive charge with negative electrons embedded throughout

Question 3

What was alpha scattering experiment

Answer 3

• Rutherford
• fired beam of alpha particles at thin gold foil

Question 4

Results + conclusions of alpha scattering experiment

Answer 4

• most went straight through - atom mostly empty space
• some deflected in random directions - repelled by positive nucleus
• few bounced back - small concentrated nucleus in centre
• led to nuclear model of atom

Question 5

Niels Bohr atom theory

Answer 5

Elections orbiting nucleus do so at certain distances on shells/energy levels

Question 6

What supported Bohr’s atom theory

Answer 6

His theoretical calculations agreed with experimental observations

Question 7

James Chadwick atom theory

Answer 7

• discovered neutron
• explained imbalance between between atomic and mass numbers

Question 8

Current model of atom

Answer 8

• small nucleus concentrates most mass in centre, contains positive protons and neutral neutrons
• mostly empty space
• electrons orbit nucleus on shells/energy levels
• equal number of protons and electrons - no overall charge

Question 9

What happens if electrons absorb EM radiation

Answer 9

They move to higher energy levels

Question 10

What happens when electrons release EM radiation

Answer 10

They move to lower energy levels

Question 11

Isotopes

Answer 11

Atoms with the same number of protons but different number of neutrons

Question 12

Radioactive decay

Answer 12

Unstable isotopes decaying into other elements to become more stable by trying to balance number of protons and neutrons in nucleus, giving out radiation

Question 13

Ionising radiation

Answer 13

Radiation that knocks electrons off atoms, creating positive ions

Question 14

Ionising power

Answer 14

How easily a radioactive source can knock electrons off atoms

Question 15

Types of radiation

Answer 15

• alpha
• beta
• gamma

Question 16

What is an alpha particle

Answer 16

• 2 protons and 2 neutrons
• like a helium nucleus

Question 17

Alpha particles penetration

Answer 17

Low

Question 18

Alpha particles range

Answer 18

cm in air

Question 19

Alpha particles ionising power

Answer 19

High

Question 20

What stops alpha particles

Answer 20

• paper
• skin

Question 21

Why are alpha particles strongly ionising

Answer 21

They are large

Question 22

What is a beta particle

Answer 22

• fast moving electron released from nucleus when neutron turns into a proton
• hardly any mass
• charge of -1

Question 23

Beta particle penetration

Answer 23

Moderate

Question 24

Beta particle range

Answer 24

Metres in air

Question 25

Beta particle ionising power

Answer 25

Moderate

Question 26

What stops beta particles

Answer 26

Around 5mm of aluminum

Question 27

Uses of alpha radiation

Answer 27

Smoke detectors - ionises air particles causing current to flow, if smoke it binds to ions, current stops, alarm sounds

Question 28

Use of beta radiation

Answer 28

Beta emitters - test thickness of sheets of metal as particles are not immediately absorbed by material

Question 29

What is gamma radiation

Answer 29

Rays of electromagnetic radiation released by nucleus

Question 30

Gamma radiation penetration

Answer 30

High

Question 31

Gamma radiation range

Answer 31

Km in air

Question 32

Gamma radiation ionising power

Answer 32

Low

Question 33

Why is gamma radiation lowly ionising

Answer 33

- waves tend to pass through rather than collide with atoms - eventually hit something and do damage

Question 34

What stops gamma radiation

Answer 34

- sheets of lead - metres of concrete

Question 35

Uses of gamma radiation

Answer 35

Radiotherapy for cancer - rays directed at cancer cells, avoiding healthy cells

Question 36

Form of nuclear equations

Answer 36

- atom before decay —> atom after decay + radiation emitted - total mass and atomic numbers must be equal on both sides

Question 37

Effect of alpha decay on nucleus

Answer 37

- atomic number decreases by 2 - atomic mass decreases by 4

Question 38

Effect of beta decay on nucleus

Answer 38

Atomic number increases by 1 (gained proton)

Question 39

Effect of gamma rays on nucleus

Answer 39

No effect

Question 40

What device measures radiation

Answer 40

Geiger-Muller tube and counter

Question 41

What does Geiger-Muller tube and counter measure

Answer 41

Count-rate

Question 42

Count-rate

Answer 42

Number of radiation counts reaching Geiger-Muller tube and counter per second

Question 43

Effect of radioactive decay being random

Answer 43

You can’t predict which nucleus in a sample will decay next and when

Question 44

Half-life

Answer 44

- time taken for the number of radioactive nuclei in an isotope to halve - time taken for the activity to fall to half of its initial value

Question 45

Use of half-life

Answer 45

- can make predictions about radioactive sources - can find source’s activity

Question 46

Activity

Answer 46

Rate at such radioactive source decays

Question 47

What is activity measured in

Answer 47

Becquerels (Bq)

Question 48

What is a becquerel

Answer 48

1 Bq is 1 decay per second

Question 49

What happens to activity and radioactivity of a source over time

Answer 49

Decreases as older sources emit less radiation

Question 50

When does activity reach 0

Answer 50

Never

Question 51

Why is activity higher than count-rate

Answer 51

Not all the radiation emitted by the sample is detected because the radiation spreads out

Question 52

Risk of using radiation

Answer 52

Ionising radiation can enter living cells and ionise their atoms, damaging (which can cause cancer) or killing them

Question 53

Irradiation

Answer 53

Exposure to radiation

Question 54

How to reduce effects of irradiation

Answer 54

- keeping sources in lead-lined boxes - standing behind barriers when using sources - keeping source in different room and handling with remote controlled arms

Question 55

Contamination

Answer 55

Radioactive particles getting onto objects

Question 56

Dangers of contamination

Answer 56

- contaminating atoms on skin may decay, releasing radiation and causing you harm - radioactive particles could get inside your body

Question 57

How to prevent contamination

Answer 57

- using gloves and tongs when handling sources to avoid particles getting stuck under nails - wearing protective suits to stop breathing in particles

Question 58

Most dangerous sources of radiation outside body

Answer 58

- beta - gamma

Question 59

Why are beta and gamma radiation most dangerous outside the body

Answer 59

They can penetrate the body and get to delicate organs

Question 60

Why is alpha radiation less dangerous

Answer 60

It can’t penetrate skin and is easily blocked by a small air gap

Question 61

Most dangerous radiation source inside body

Answer 61

Alpha

Question 62

Why is alpha most dangerous radiation source in body

Answer 62

- highly ionising - can ionise and damage/kill cells - do all their damage in localised area

Question 63

Largest concern when working with alpha sources

Answer 63

Contamination - alpha radiation does damage inside of body

Question 64

Why are beta sources less damaging in body

Answer 64

Radiation is absorbed over a wider area and some passes out of the body altogether

Question 65

Least dangerous radiation source inside body

Answer 65

Gamma

Question 66

Why is gamma least dangerous inside body

Answer 66

- mostly passes straight out - lowest ionising power