atomic structure

Question 1

Describe the John Dalton model of the atom.

Answer 1

Indivisible solid spheres of matter. Each element was a different sphere.

Question 2

What particle did JJ Thompson discover that caused the atomic model to change?

Answer 2

The electron.

Question 3

Describe the atomic model developed by JJ Thompson.

Answer 3

The ‘plum pudding’ model. A cloud of positive charge with negative electrons scattered within it.

Question 4

Describe Rutherford’s gold foil scattering experiment.

Answer 4

Tiny positive alpha particles were fired at a thin piece of gold foil in a vacuum chamber.

Question 5

What three observations were made during the gold foil scattering experiment?

Answer 5

• Most alpha particles passed straight through.
• Some alpha particles were deflected by less than 90°.
• Very few alpha particles were deflected by more than 90°.

Question 6

What three conclusions were made following the alpha scattering experiment?

Answer 6

• Most of the atom is empty space.
• There must be a region of concentrated positive charge.
• There must be a very small, dense nucleus that contains most of the atom’s mass.

Question 7

Describe Rutherford’s nuclear model.

Answer 7

A positive nucleus surrounded by electrons. Most of the atom is empty space.

Question 8

How did Neils Bohr change the atomic model?

Answer 8

He stated that electrons can only orbit the nucleus at set energy levels (shells) - planetary model.

Question 9

How did James Chadwick add to the atomic model?

Answer 9

He discovered neutrons.

Question 10

Name the three subatomic particles.

Answer 10

• Proton
• Neutron
• Electron

Question 11

Which subatomic particles are located in the nucleus of an atom?

Answer 11

• Protons
• Neutrons

Question 12

Where are electrons located in the atom?

Answer 12

In energy levels (shells) around the nucleus.

Question 13

What is the relative charge of each subatomic particle?

Answer 13

• Proton: +1
• Neutron: 0
• Electron: -1

Question 14

What is the relative mass of each subatomic particle?

Answer 14

• Proton: 1
• Neutron: 1
• Electron: 0.0005 (1/2000)

Question 15

Define ‘atom’.

Answer 15

The smallest part of an element that can still be identified as that element.

Question 16

What is the approximate radius of an atom?

Answer 16

1 x 10^-10 m

Question 17

What is most of an atom made up of?

Answer 17

Empty space.

Question 18

What is the overall electric charge on an atom?

Answer 18

zero/neutral.

Question 19

Define ‘element’.

Answer 19

A substance that contains only one type of atom.

Question 20

Define ‘atomic number’.

Answer 20

The number of protons in an atom.

Question 21

What number defines which element an atom is?

Answer 21

The atomic (proton) number.

Question 22

Why is the overall charge of an atom zero?

Answer 22

Atoms contain the same number of positively charged protons as negatively charged electrons.

Question 23

Define ‘mass number’.

Answer 23

The total number of protons and neutrons in the nucleus of an atom.

Question 24

Define ‘isotope’.

Answer 24

An atom of the same element with different numbers of neutrons in the nucleus.

Question 25

Define 'ion'.

Answer 25

An atom that has lost or gained electrons so that it becomes electrically charged.

Question 26

Absorption of radiation by an atom may result in ____________ moving to a ________________ energy level.

Answer 26

electrons, higher.

Question 27

What does it mean when an electron is ‘excited’?

Answer 27

It has gained energy and moved to a higher energy level.

Question 28

Emission of radiation from an atom may lead to _____________ moving to a ______________ energy level.

Answer 28

electrons, lower.

Question 29

What is emitted when electrons become ‘de-excited’?

Answer 29

Waves (e.g. Light, Infra-red) are emitted as electrons fall back to a lower energy level.

Question 30

How can an atom be ionised by radiation?

Answer 30

When an outer shell electron gains enough energy to be completely removed from the atom.

Question 31

If ionisation happens in DNA it can cause ___________ which may result in ____________.

Answer 31

mutations, cancer.

Question 32

Why might a nucleus be unstable?

Answer 32

The forces within the nucleus are unbalanced.

Question 33

What is 'radioactive decay'?

Answer 33

When an unstable nucleus changes to become more stable by giving out radiation.

Question 34

What is ionising radiation?

Answer 34

A particle or energy that is able to liberate outer shell electrons from atoms.

Question 35

Name the three types of naturally occurring ionising radiation.

Answer 35

* Alpha * Beta * Gamma

Question 36

What is a 'radioactive substance'?

Answer 36

A substance that spontaneously gives out radiation from the nuclei of its atoms.

Question 37

Why do we describe radioactive decay as random?

Answer 37

Because we cannot predict when a given nucleus will decay.

Question 38

What is 'nuclear radiation'?

Answer 38

A collective term for the particle and/or energy that is emitted when an unstable nucleus decays.

Question 39

What is an alpha particle?

Answer 39

Two protons and two neutrons - a helium nucleus.

Question 40

Write the symbol for alpha radiation.

Answer 40

𝛂.

Question 41

During an alpha decay, how does the atomic number change?

Answer 41

Decreases by 2.

Question 42

During an alpha decay, how does the mass number change?

Answer 42

Decreases by 4.

Question 43

What is a beta particle?

Answer 43

A fast moving electron.

Question 44

Write the symbol for beta radiation.

Answer 44

𝛃.

Question 45

Describe the decay within the nucleus that leads to a beta emission.

Answer 45

A neutron decays into a proton and electron and the electron is ejected from the nucleus.

Question 46

During a beta decay, how does the atomic number change?

Answer 46

Increases by 1.

Question 47

During a beta decay, how does the mass number change?

Answer 47

Mass number does not change.

Question 48

What is gamma radiation?

Answer 48

A high energy (electromagnetic) wave.

Question 49

Write the symbol for gamma radiation.

Answer 49

𝛄.

Question 50

What is the range of alpha radiation in air?

Answer 50

Short - a few cm in air.

Question 51

What is the range of gamma radiation in air?

Answer 51

More than 1m.

Question 52

What's the range of beta radiation in air?

Answer 52

Less than 1m.

Question 53

What will absorb (stop) alpha radiation?

Answer 53

Paper or skin.

Question 54

What will absorb (stop) beta radiation?

Answer 54

A few mm of aluminium.

Question 55

What will absorb (stop) gamma radiation?

Answer 55

Several centimetres of lead or concrete.

Question 56

What is the ionising power of alpha radiation?

Answer 56

Very high.

Question 57

What is the ionising power of beta radiation?

Answer 57

Medium - less than alpha but more than gamma.

Question 58

What is the ionising power of gamma radiation?

Answer 58

Low (compared to alpha and beta - still dangerous!).

Question 59

Define 'activity' of a source.

Answer 59

The number of decays per second.

Question 60

What are the units of activity?

Answer 60

Becquerels (Bq).

Question 61

What does an activity of 7Bq mean?

Answer 61

7 decays per second.

Question 62

Define 'count rate'.

Answer 62

Number of decays per second measured by detector.

Question 63

Why is the count rate different to the activity?

Answer 63

We cannot measure all radioactive decays that occur.

Question 64

Define 'half life'.

Answer 64

The time taken for the number of radioactive nuclei in a sample to halve.

Question 65

What is radioactive 'contamination'?

Answer 65

The unwanted presence of materials containing radioactive atoms.

Question 66

Define 'irradiation'.

Answer 66

When an object is exposed to ionising radiation.

Question 67

Does an irradiated object become radioactive itself?

Answer 67

No.