4. Atomic Structure

Question 1

What is the approximation for the radius of an atom?

Answer 1

1x10⁻¹⁰ metres.

Question 2

What are the three subatomic constituents of an atom?

Answer 2

1. Proton 2. Neutron 3. Electron

Question 3

Where is most of the mass of an atom concentrated?

Answer 3

In the nucleus.

Question 4

What proportion of the total radius of an atom is the radius of the nucleus?

Answer 4

1/10000th

Question 5

Describe the arrangement of protons

Answer 5

neutrons

Question 6

What charge does the nucleus of an atom have? Why?

Answer 6

• Positive charge. - The nucleus contains protons (positive charge) and neutrons (no charge).

Question 7

Give two ways that an atom’s electron arrangement can be changed.

Answer 7

1. Absorbing electromagnetic radiation. 2. Emitting electromagnetic radiation.

Question 8

How does an atom’s electron arrangement change when it absorbs EM radiation?

Answer 8

Electrons move further away from the nucleus (higher energy level).

Question 9

How does an atom’s electron arrangement change when it emits EM radiation?

Answer 9

Electrons move closer to the nucleus (lower energy level).

Question 10

How does the ratio of electrons to protons result in the atom having no overall charge?

Answer 10

The number of protons equals the number of electrons, and their charges cancel each other out.

Question 11

What do all forms of the same element have in common?

Answer 11

They all have the same number of protons.

Question 12

What is the atomic number?

Answer 12

The number of protons in an atom.

Question 13

What is an atom’s mass number?

Answer 13

The total number of protons and neutrons in the atom.

Question 14

What is an isotope?

Answer 14

An atom of an element that has a different number of neutrons but the same number of protons.

Question 15

How do atoms turn into positive ions?

Answer 15

By losing one or more electrons.

Question 16

What may lead to a scientific model being changed or replaced?

Answer 16

Discovery of new experimental evidence that doesn’t agree with the existing theory.

Question 17

How did the plum-pudding model describe the atom?

Answer 17

A ball of positive charge with negatively charged electrons distributed evenly throughout.

Question 18

Prior to the discovery of the electron

Answer 18

what was believed about the atom?

Question 19

Which experiment led to the plum-pudding model being discarded?

Answer 19

Rutherford’s alpha-scattering experiment.

Question 20

What is the currently accepted model of the atom?

Answer 20

The Bohr nuclear model.

Question 21

What were the conclusions of Rutherford’s alpha-scattering experiment?

Answer 21

1. Most of the mass is concentrated in the nucleus. 2. The nucleus is positively charged.

Question 22

What reinforces a scientific theory?

Answer 22

When experimental results agree with theoretical predictions.

Question 23

What did James Chadwick’s experiments prove?

Answer 23

The existence of neutrons.

Question 24

Why do unstable nuclei give out radiation?

Answer 24

To become more stable by undergoing radioactive decay.

Question 25

What is radioactive decay?

Answer 25

The process where an unstable nucleus emits radiation to become more stable.

Question 26

Define the activity of an unstable nucleus.

Answer 26

The rate of decay of a source of unstable nuclei.

Question 27

What is the unit of radioactive activity?

Answer 27

Becquerel (Bq).

Question 28

What is count-rate?

Answer 28

The number of radioactive decays per second for a radioactive source.

Question 29

Give an example of a detector used to measure count-rate.

Answer 29

Geiger-Muller tube.

Question 30

What are the four types of nuclear radiation?

Answer 30

1. Alpha particles 2. Beta particles 3. Gamma rays 4. Neutrons

Question 31

What are the constituents of an alpha particle?

Answer 31

Two protons and two neutrons (same as a helium nucleus).

Question 32

What is the range of an alpha particle through air?

Answer 32

A few centimetres (typically 2-10 cm).

Question 33

What will stop beta radiation?

Answer 33

A thin sheet of aluminium or several metres of air.

Question 34

What will stop gamma radiation?

Answer 34

Several centimetres of lead or a few metres of concrete.

Question 35

Which type of radiation is most ionising?

Answer 35

Alpha radiation.

Question 36

Which type of radiation is least ionising?

Answer 36

Gamma radiation.

Question 37

State any changes to mass or charge due to emission of a gamma ray.

Answer 37

Both mass and charge remain unchanged.

Question 38

Describe the nature of radioactive decay.

Answer 38

- Random. - Which nucleus decays and when is determined by chance.

Question 39

Define the half-life of a radioactive isotope.

Answer 39

1. The time it takes for the number of unstable nuclei in a substance to halve. 2. The time it takes for the count rate to halve.

Question 40

What is radioactive contamination?

Answer 40

The presence of unwanted radioactive nuclei on other materials.

Question 41

What is irradiation?

Answer 41

The process of exposing a material to nuclear radiation (the material does not become radioactive).

Question 42

Why is it important to publish studies on the effects of radiation?

Answer 42

To allow findings to be independently checked (peer review).