Topic 4 - Atomic Structure

Question 1

What are the 5 stages in the development of the atom?

Answer 1

Dalton: Solid ball of non-divisible, very dense mass
Thompson: Plum pudding - solid ball of positive charge with small negatively charged balls within it
Rutherford: Nuclear - small and dense positive mass in the centre with surrounding negatively charged masses, mostly empty space
Bohr: Electrons held in energy shells but nucleus was indivisible
Chadwick: Neutrons and protons in the nucleus with electrons in fixed shells surrounding

Question 2

Describe the alpha scattering experiment

Answer 2

Alpha particles, which have a positive charge, were fired at thin gold foil and their movements were measured

Question 3

What were the results and how did they affect our view of the atom?

Answer 3

The majority of the atoms passed straight through, unaffected - most of the atom is empty space
Some were pushed off of their original path - there is a positive mass somewhere in the atom
Some were deflected - the positive mass is very small and dense
^^The plum pudding model couldn’t explain this

Question 4

Why are protons and electrons directly proportional?

Answer 4

This is so that the overall charge of an atom is negative

Question 5

What happens when protons and electrons are not equal?

Answer 5

The atom become a charged particles called an ion

Question 6

Define an isotope

Answer 6

Atoms of an element with the same number of protons but a different number of neutrons

Question 7

Define radioactive decay

Answer 7

Atoms decaying into other elements and giving out radiation as they try to become more stable

Question 8

What are alpha particles?

Answer 8

Helium nuclei

Question 9

What are beta particles?

Answer 9

Fast-moving electrons

Question 10

What are gamma rays?

Answer 10

Electromagnetic waves with a short wavelength

Question 11

What are the properties of alpha particles?

Answer 11

They are stopped very quickly, they can only travel a few cm in air and won’t penetrate and piece of paper but because of their size they are highly ionising

Question 12

Define ionising

Answer 12

When ionising particles collide with atoms they will knock electrons off of them

Question 13

What are the properties of beta particles?

Answer 13

They are moderately ionising and they can travel farther than alpha particles, for every beat particles emitted, a neutron turns into an electron

Question 14

What are the properties of gamma radiation?

Answer 14

They are very penetrating and can travel long distances, they are weakly ionising as they tend to pass through atoms rather than collide with them, they will eventually do something and cause damage

Question 15

What are nuclear eqautions?

Answer 15

A way of showing radioactive decay using element symbols

Question 16

Why does the atomic number decrease by 2 but the mass number decreases by 4 when an alpha particle is emitted from an atom?

Answer 16

An alpha particle is a helium nucleus and whilst protons are positively charged, neutrons just have a mass no charge

Question 17

What happens to the atomic number of an element when a beta particle is emitted?

Answer 17

It increases by 1 because an electron is negatively charged and has an atomic number of -1

Question 18

What is a half life?

Answer 18

The time taken for the number of radioactive nuclei in an isotope to halve

Question 19

T/F: radioactive substances give out radiation from the nuclei of their atoms under specific circumstances

Answer 19

False: radioactive substances give out radiation from the nuclei of their atoms no matter what

Question 20

What does a Geiger-Muller tube and counter do?

Answer 20

Measures the number of counts of radiation reaching it per second

Question 21

What can half lifes be used for?

Answer 21

1. Measuring the time it takes for radiation to be emitted/the rate it takes a source to decay
2. Carbon dating

Question 22

Does the radioactive activity of a decaying source ever reach zero?

Answer 22

No. It just keeps on halving .e.g. 1/16 –> 1/32 –> 1/64 –> 1/128

Question 23

Give an alternative definition of a half life in terms of activity

Answer 23

The time taken for the activity of a radioactive source to halve

Question 24

Are sources with a longer or shorter half life more dangerous?

Answer 24

Sources with a shorter half life are more dangerous because they are emitting more radiation faster but sources with a long half life are still dangerous

Question 25

Name some sources of background radiation (6 in total)

Answer 25

1. Air
2. Food
3. Building materials
4. Rocks under our feet
5. Cosmic rays from the sun (our atmosphere stops the majority of that radiation)
6. Human activity .i.e. nuclear explosions or waste

Question 26

Define irradiation

Answer 26

Irradiation is another way of saying ‘exposed to radiation’

Question 27

T/F: irradiating something makes it radioactive

Answer 27

False: it doesn’t

Question 28

Give three ways to prevent irradiation

Answer 28

1. Keeping sources in lead-lined boxes
2. Standing behind a barrier or in a different room
3. Using remote-controlled arms to work for irradiating substances

Question 29

Define contamination

Answer 29

The unwanted presence of a radioactive source on a substance

Question 30

Why is contamination so dangerous?

Answer 30

Having radioactive sources in an uncontrolled environment can lead to harm of other people and also yourself - the danger is increased if the source enters the body

Question 31

How can you prevent contamination?

Answer 31

By wearing gloves when handling radioactive sources to stop is getting on your hands or stuck under fingernails and you may also wear a mask to prevent the inhalation of particles

Question 32

Which sources are most and least harmful within the body and why?

Answer 32

Alpha radiation is the most dangerous within the body because they do their damage in a very local area whereas gamma radiation is least dangerous because it will pass straight out of the body and has the lowest ionising power

Question 33

Which sources are most dangerous outside of the body?

Answer 33

Beta and gamma because they can easily penetrate skin in order to access valuable organs but high levels of irradiation from any source is dangerous

Question 34

How are gamma sources used in medicine?

Answer 34

They can be used as medical tracers - this is done by injecting a small amount of a radioactive substance into the person into the body which will perform a particular role and show the doctors how that person’s bodily functions are working

Question 35

Describe the process of radiotherapy

Answer 35

Gamma rays are directed carefully and in the right dosage towards cancerous cells in a tumour and kills them without damaging too many normal body cells

Question 36

What is the disadvantage of radiotherapy?

Answer 36

Some normal cells are going to be damaged in the process and consequently the patient can end up feeling pretty rubbish and ill

Question 37

What are the risks of using radiation?

Answer 37

A large dose of radiation can kill of healthy cells completely
A smaller dose doesn’t kill them but it causes them to mutate and divide uncontrollably - this is cancer

Question 38

Describe the process of nuclear fission

Answer 38

1. A neutron is absorbed by an atom causing it to split in two
2. Two or three more neutrons can also be released during the process
3. These may be moving slow enough to be absorbed by another nucleus which leads to a chain reaction
4. This process releases a lot of energy

Question 39

How do nuclear weapons work?

Answer 39

This is when uncontrolled chain reactions cause lots of energy to be released quickly in an explosion

Question 40

What is nuclear fission used for?

Answer 40

Nuclear fission is used in nuclear reactors and power plants and they harness the energy that was released in the reaction

Question 41

What is nuclear fusion?

Answer 41

Fusion is when two nuclei collide and fuse to form one in very high temperatures, releasing energy and a helium nucleus in the process

Question 42

How do we benefit from nuclear fusion?

Answer 42

The sun has nuclear fusion occurring within it consistently and we are very dependent on the sun