P4 - Atomic Structure

Question 1

What are atoms

Answer 1

• Atoms are very small

* Have a radius of about 1x10(-10) metres

Question 2

What is the basic structure of an atom?

Answer 2

Positively charged nucleus composed of both protons and neutrons surrounded by negatively charged electrons

Question 3

What is the radius of a nucleus

Answer 3

Less than 1/10000 of the radius of an atom

Question 4

Where is most of the mass of an atom concentrated

Answer 4

In the nucleus

Question 5

Electron arrangement (3)

Answer 5

• Electrons are arranged at different distances from the nucleus (different energy levels)
• Electron arrangements may change with the absorption of electromagnetic radiation
• Electron arrangement may also change by the emission of electromagnetic radiation

Question 6

In an atom, what is the number of electrons equal to

Answer 6

The number of protons in the nucleus - so they have no overall electrical charge

Question 7

What do all atoms of a particular element have

Answer 7

The same number of protons

Question 8

Atomic number

Answer 8

(bottom) Is the number of protons in an atom of an element

Question 9

Mass number

Answer 9

• Is the total number of protons and neutrons in an atom

* Is at the top

Question 10

What do atoms of the same element have?

Answer 10

Different number of neutrons - these are called isotopes of that element

Question 11

Isotopes

Answer 11

Occur when atoms of the same element have a different number of neutrons

Question 12

What do atoms turn into when they lose one or more outer electrons

Answer 12

Positive ions

Question 13

Differences between isotopes to differences in conventional representations of their identities, charges and masses (3)

Answer 13

• Some atomic nuclei are unstable
• The nucleus gives out radiation as it changes to become more stable
• This is a random process called radioactive decay.

Question 14

Before the discovery of the electron what were atoms thought to be

Answer 14

Tiny spheres that could not be divided

Question 15

Plum pudding model

Answer 15

Suggested that the atom is a ball of positive charge with negative electrons embedded in it

Question 16

What was the conclusion made from the results of the alpha particle scattering experiment (2)

Answer 16

• That the mass of an atom was concentrated at the centre (nucleus) and that the nucleus was charged
• This nuclear model replaced the plum pudding model

Question 17

How did Niels Bohr adapt the nuclear model

Answer 17

By suggesting that electrons orbit the nucleus at specific distances

Question 18

What did later experiments (after Niels Bohr) lead to the idea of (3)

Answer 18

• Led to the idea that the positive charge of any nucleus could be subdivided into a whole number of smaller particles
• Each particle having the same amount of positive charge
• The name proton was given to these particles

Question 19

Whose work provided evidence to show the existence of neutrons within the nucleus

Answer 19

James Chadwick’s

Question 20

Why did the new evidence from the alpha particle scattering experiment lead to a change in the atomic model? (2)

Answer 20

• From the plum pudding model, they expected the particles to pass straight through the gold sheet or only be slightly deflected
• But although most of the particles did go straight through the sheet, some were deflected more than expected and a few were deflected back - which the plum pudding could not explain

Question 21

Plum pudding model

Answer 21

Suggested that atoms were spheres of positive charge with tiny negative electrons struck in them like fruit in a plum pudding

Question 22

Nuclear model (2)

Answer 22

• Realised that most of the mass of the atom must be concentrated at the centre in a tiny nucleus - this must also have a positive charge
• realised most of the atom is empty space

Question 23

Atomic nuclei

Answer 23

• Are unstable
• The nucleus gives out radiation as it changes to become more stable
• This is a random process called radioactive decay

Question 24

Activity

Answer 24

• Is the rate at which a source of unstable nuclei decays

* Measured in becquerel (Bq)

Question 25

Count rate

Answer 25

Is the number of decays recorded each second by a detector (e.g Geiger-Muller tube)

Question 26

4 ways nuclear radiation may be emitted

Answer 26

• Alpha particle (a)
• Beta particle (ß)
• Gamma ray (y)
• neutron (n)

Question 27

Alpha particle (a)

Answer 27

Consists of two neutrons and two protons, it is the same as a helium nucleus

Question 28

Beta particle (ß)

Answer 28

A high speed electron ejected from the nucleus as a neutron turns into a proton

Question 29

Gamma ray (y)

Answer 29

• Electromagnetic radiation from the nucleus

Question 30

Symbol for an alpha particle

Answer 30

Check photos

Question 31

Symbol for a beta particle

Answer 31

Check photos

Question 32

What is the half-life of a radioactive isotope? (2)

Answer 32

• Is the time it takes for the number of nuclei of the isotope in a sample to halve,
• Or the time it takes for the count rate (or activity) from a sample containing the isotope to fall to half its initial level

Question 33

How to calculate the final activity as a percentage of the initial activity (2)

Answer 33

• Find the activity after each half-life

* Now divide the final activity by the initial activity, then multiply by 100 to make it a percentage

Question 34

What is radioactive contamination?

Answer 34

Is the unwanted presence of materials containing radioactive atoms on other materials

Question 35

What is the hazard from contamination due to?

Answer 35

The decay of the contaminating atoms- the type of radiation emitted affects the level of hazard

Question 36

What is irradiation? (2)

Answer 36

• Is the process of exposing an object to nuclear radiation

* The irradiated object does not become radioactive

Question 37

Hazards associated with irradiation and contamination (2)

Answer 37

• Cancers - as it can damage cells

* mainly cause harm

Question 38

Why are findings of studies into the effects of radiation on humans important?

Answer 38

To be published and shared with other scientists so that the findings can be checked by peer review