P4

Question 1

Characteristics of an atom

Answer 1

Items are very small, having a radius of about 1×10^-10 metres

Question 2

What is the basic structure of an atom?

Answer 2

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

Question 3

What is the radius of the nucleus?

Answer 3

The radius of a nucleus is less than 1/10000 of the radius of an atom, most of the mass of an atom is concentrated in the nucleus

Question 4

How do the electron arrangements change?

Answer 4

• The electrons arranged at different distances from the brackets (different energy levels).
• The electron arrangement may change with the absorption of electromagnetic magnetic radiation move (further from the nucleus; a higher energy level) or by the invention of electromagnetic radiation (move closer to the nucleus; a lower energy level)

Question 5

What charge do atoms have and why?

Answer 5

Atoms have no overall electrical charge as in an atom, the numbers of electrons is equal to the number of protons in the nucleus

Question 6

What is the mass number of an element?

Answer 6

The total number of protons and neutrons in an atom

Question 7

What is the atomic number of an element?

Answer 7

The number of protons and electrons in the atom

Question 8

What are isotopes?

Answer 8

Isotopes of an element are atoms with the same number of protons (the same atomic number, and so the same charge on the nucleus) but a different number of neutrons (a different mass number). E.g. (18top 8bottom)O is an isotope of oxygen.

Question 9

If elements lose electrons in their outer shell what do the atoms turn into?

Answer 9

Positive ion

Question 10

What are similarities in the same isotopes?

Answer 10

They share similar chemical properties

Question 11

All elements have different isotopes, though how many stable isotopes are there?

Answer 11

One or two

Question 12

Note:

Answer 12

Go to page 196 and see how isotopes are

Question 13

What do new experimental evidence do to scientific models?

Answer 13

Leads them to be changed or replaced

Question 14

What were electrons thought to be before its discovery?

Answer 14

Atoms were thought to be tiny spheres that could not be divided (this was before 1897)

Question 15

What happened after the discovery of the electron (1897)?

Answer 15

• The discovery of the electron led to the plum pudding model of the atom
• JJ Thompson suggested The plum pudding model, that the atom is a pool of positive charge with negative electrons embedded in it

Question 16

What happened in 1909 with Rutherford’s experiment?

Answer 16

• They conducted the famous alpha particle scattering experiments
• They fired positively charged alpha particles at an extremely thin sheet of gold
• From the plum pudding model,they were expecting the particles to pass straight through the sheet or be slightly deflected at most
• This was because the positive charge of each atom was though to be very spread out through the pudding of the atom
• But,whilst most of the particles did go straight through the sheet,some were deflected more than expected,and a small number were deflected backwards
• So the plum pudding model could not be right

Question 17

What did the Rutherford experiment do as a result?

Answer 17

The results from the alpha particle scattering experiment lead to the conclusion that the mass of an atom is concentrated at the centre (nucleus), and that the nucleus was charged this nuclear model replace the pump pudding model

The nuclear model of the atom.In this a tiny,positive charged nucleus at the centre,where most of the mass is concentrated.A ‘cloud’ of negative electrons surrounds this nucleus - so most of the atom is empty space.

These were the conclusions because even though most alpha particles passed through, some bounced back.

Question 18

What did Niels Bohr do to the nuclear model?

Answer 18

• He adopted the nuclear model by suggesting that electrons orbit, the nucleus at specific distances
• The theoretical calculations of Bohr agreed with the experimental observations

Question 19

What did James Chadwick discover in 1932?

Answer 19

About 20 years after the idea of a nucleus was accepted, in 1932, James Chadwick proved the existence of the neutron, which explained the imbalance between the atomic and mass numbers

Question 20

The differences between the plum pudding model of the atom and the nuclear model of the atom

Answer 20

• Plum pudding model mass is distributed evenly
• Plum pudding model is a solid mass
• Plum pudding electrons embedded in the mass of positive charge
• Nuclear model positive charge occupies only a small part of the atom
• Nuclear model electrons orbit some distance from the centre
• Nuclear model the atom is mainly empty space
• Nuclear model mass is concentrated in the centre

Question 21

As some nuclei are unstable, what does this lead to?

Answer 21

The other unstable isotopes tend to decay into other elements and give out radiation as they try to become more stable (they fry to balance the number of protons and neutrons in their nucleus or get rid of any excess energy). This process is called radioactive decay

Question 22

What is activity?

Answer 22

Activity is the richest source of unstable nuclei decays. Activity is measured in becquerel(Bq)

Question 23

What is count-rate?

Answer 23

Count-rate is the number of decays recorded each second by a detector (e.g Geiger-Müller tube)

Question 24

What are the different types of nuclear radiation?

Answer 24

• An alpha particle
• A beta particle
• A gamma ray
• A neutron

Question 25

What are the characteristics of an alpha particle?

Answer 25

An alpha particle(a) - This consists of two neutrons and two protons(like a helium nucleus) They don't penetrate very far into materials and are stopped quickly - they can only travel a few cm in air and are absorbed by a sheet of paper

Question 26

What are the characteristics of an beta particle?

Answer 26

- A beta particle (B) is simply a fast-moving electron released by the nucleus - Beta particles have virtually no mass and a charge of -1 - They are moderately ionising. They penetrate moderately far into materials before colliding and have a range in air of a few metres They are absorbed by a sheet of aluminium (around 5 mm) - For every beta particle emitted, a neutron in the nucleus has turned into a proton

Question 27

What are the characteristics of a gamma ray?

Answer 27

- Gamma rays (y) are waves of electromagnetic radiation released by the nucleus - They penetrate far into materials without being stopped and will travel a long distance through air - This means they are weakly ionising because they tend to pass through rather than collide with atoms. Eventually they hit something and do damage - They can be absorbed by thick sheets of lead or metres of concrete

Question 28

What is radiation used for in todays society?

Answer 28

Today, to benefit humankind, radiation is used in medicine, academics, and industry, as well as for generating electricity. In addition, radiation has useful applications in such areas as agriculture, archaeology (carbon dating), space exploration, law enforcement, geology (including mining), and many others

Question 29

Note:

Answer 29

Check page 197 and see how nuclear equations work

Question 30

What does the emission of different types of nuclear radiation cause?

Answer 30

A change in mass or a change of the nucleus

Question 31

What does alpha decay cause?

Answer 31

Both the mass and charge of the nucleus to decrease

Question 32

What does beta decau cause?

Answer 32

Beta decay does not cause the mass of the nucleus to change but does cause the charge of the nucleus to increase

Question 33

What does gamma ray cause?

Answer 33

Gamme ray does not cause the mass or the charge of the nucleus to change

Question 34

Note:

Answer 34

Students should be able to use the names and symbols of common nuclei and particles to write balanced equations that show single alpha (a) and beta (B) decay. This is limited to balancing the atomic numbers and mass numbers. The identification of daughter elements from such decays is not required.

Question 35

Is radioactive decay fixed or random?

Answer 35

- Radioactive decay is entirely random - So you can't predict exactly which nucleus in a sample will decay next, or when any one of them will decay

Question 36

What is half-life of a radioactive isotope?

Answer 36

You can find out the time it takes for the amount of radiation emitted by a source to halve. It can be used to make predictions about radioactive sources, even though their decays are random. Half-life can be used to find the rate at which a source decays - its ACTIVITY. Activity is measured in becquerels, Bq (where 1 Bq is I decay per second)

Question 37

Concept of half-life

Answer 37

- Half-life is the time it takes for half of the unstable nuclei in a sample to decay or for the activity of the sample to halve or for the count rate to halve. - Count-rate is the number of decays recorded each second by a detector, such as the Geiger-Muller tube

Question 38

Note:

Answer 38

Hey, AQA says that student should be able to determine the half life of a radioactive isotopes given information The initial activity of a sample is 640 Bq. Calculate the final activity as a percentage of the initial activity after two half-lives. 1) Find the activity after each half-life. 2) Now divide the final activity by the initial activity, 2 half-lives: 320 ÷ 2 = 160 then multiply by 100 to make it a percentage,ratio or decimal depending on what the question asks for

Question 39

Note:

Answer 39

AQA says students should be able to calculate the net secline expressed as a ratio in radioactive admission after a given number of half lives

Question 40

What is radioactive contamination?

Answer 40

- Radioactive contamination is the unwanted presence of materials containing radioactive atoms of other materials - The Hazard from contamination is due to the decay of the contaminating atoms - The type of radiation emitted affects the level of the hazard

Question 41

What is irradation?

Answer 41

- Irritation is the process of exposing an object of nuclear radiation - The irritated object does not become radioactive

Question 42

State the hazards associated with contamination

Answer 42

- Radioactive isotopes may not go where they are wanted - It can be difficult to ensure that the contamination is fully removed so small amounts of radioisotope may still be left behind - Exposure to radioactive materials can potentially damage healthy cells

Question 43

State the hazards associated with irridation

Answer 43

- it may not kill all bacteria on an object it can be very harmful - standing in the environment where objects are being treated by irradiation could expose people’s cells to damage and mutation

Question 44

What is the most dangerous radiation outside the body?

Answer 44

- Beta and gamma sources, This is because beta and gamma can penetrate the body and get to the delicate organs - Alpha is less dangerous because it can't penetrate the skin and is easily blocked by a small air gap

Question 45

What is the most dangerous radiation inside the body?

Answer 45

- Alpha sources, because they do all their damage in a very localised area - So contamination, rather than irradiation, is the major concern when working with alpha sources - Beta sources are less damaging inside the body, as radiation is absorbed over a wider area, and some passes out of the body altogether - Gamma sources are the least dangerous inside the body, as they mostly pass straight out - they have the lowest ionising power

Question 46

What precautions must be taken to protect against any hazard that the radiactive source used in the process of irridation may present

Answer 46

- Keeping radioactive sources shielded when not in use, for example in a lead-lined box - Wearing protective clothing to prevent the body becoming contaminated - Limiting exposure time so less time is spent with radioactive materials - Handling radioactive materials with tongs to increase the distance from them - Monitoring exposure using detector badges

Question 47

Note:

Answer 47

AQA says It is important for the findings of studies into effects of radiation on humans to be published and checked with other side, so that the findings can be checked by peer review