Atomic structure

Question 1

What is the radius of an atom?

Answer 1

1 × 10 to the power of -10 m.

Question 2

What are the charges of protons and electrons?

Answer 2

Protons= +1
Electrons= -1

Question 3

How is electromagnetic radiation emitted?

Answer 3

When an electron drops in a lower energy level.

Question 4

What is a positive ion?

Answer 4

An atom that loses one of its outer electrons to become a positive ion.

Question 5

What is a negative ion?

Answer 5

An atom that gains an extra electron to become a negative ion.

Question 6

What is the atomic number?

Answer 6

The number of protons in an atom.

Question 7

What is the mass number?

Answer 7

Total number of protons and neutrons.

Question 8

What is an isotope?

Answer 8

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

Question 9

Who discovered the electron and when was it discovered?

Answer 9

Discovered by J.J Thompson in 1897.

Question 10

What was the plum pudding model?

Answer 10

It depicts the atom as a ball of positive charge with electrons embedded in it.

Question 11

What did Rutherford and Marsden do in 1905?

Answer 11

They bombarded thin gold foil with alpha particles.

Question 12

What happened in the Rutherford and Marsden experiment?

Answer 12

Most particles passed straight through, some particles deflected back and some particles were deflected slightly.

Question 13

What was the conclusion of the Rutherford and Marsden experiment?

Answer 13

The conclusion was that:
-the mass of the atom was concentrated in a central nucleus, which was positively charged
-the electrons surrounded this nucleus.

Question 14

How did Niels Bohr adapt this nuclear model?

Answer 14

He suggested that electrons orbit the nucleus at specific distances.

Question 15

What did James Chadwick find out in 1932?

Answer 15

He discovered the neutron.

Question 16

What is the activity of a radioactive source and what is it measured in?

Answer 16

The activity of a radioactive source is the rate at which the atom decays. Measured in becquerels (Bq).

Question 17

What are the 3 main types if nuclear radiation?

Answer 17

Alpha, Beta and Gamma

Question 18

What is the least and most ionising radiation?

Answer 18

Alpha is the most ionising and gamma is the least ionising.

Question 19

Alpha (a).

Answer 19

Components- 2 neutrons/protons. Ejected from the same nucleus.
Hazards-Highly likely to be absorbed and cause damage if passing through living cells.

Question 20

Beta (β).

Answer 20

Components- High-speed electron. Ejected from the nucleus as the nucleus turns into a proton.
Hazards-Likely to cause damage if absorbed by living cells.
-Can penetrate the body to inner organs.

Question 21

Gamma (γ).

Answer 21

Components-Electromagnetic radiation. Emitted from the nucleus.
Hazards-Likely to pass through living cells without being absorbed and causing ionisation.

Question 22

What is the 4th type of nuclear radiation?

Answer 22

It is a neutron (n) that can be emitted during radioactive decay.

Question 23

What is radioactive contamination?

Answer 23

It is the unwanted presence of materials containing radioactive atoms on other materials.

Question 24

What is irradiation?

Answer 24

-Is the process of exposing an object to nuclear radiation
-Can be deliberate or accidental
-Does not cause the object to become radioactive.

Question 25

How to protect against unwanted radiation?

Answer 25

• By Using sources of the lowest activity possible for the shortest amount of time possible.
• Wear appropriate protective clothing such as a lead apron.
• Not handling sources with bare hands.

Question 26

What is the half-life of a radioactive isotope?

Answer 26

-The average time it takes for half of the nuclei to decay.
-The time it takes for the count rate, or activity, of a sample containing the isotope to fall to 50% of its original value.

Question 27

The half-life of a radioactive isotope is 2 years and the initial activity is 800Bq. What will be the activity after 6 years?

Answer 27

2 years=1/2 count rate
4 years=1/4 count rate
6 years=1/8 count rate
final count rate=1/8 * initial activity
=1/8 * 800=100Bq

Question 28

What are the features of isotopes with short half-lives?

Answer 28

-Are very unstable and emit radiation very quickly so exposure can be very hazardous.
-Do not remain radioactive for very long.

Question 29

What are the features of isotopes with short half-lives?

Answer 29

-Are more stable and remain radioactive for a very long time.
-Emit radiation slowly, so exposure is less hazardous.

Question 30

How is nuclear radiation used in medical tracers?

Answer 30

They are used to look at internal organs.
-A radioactive isotope is ingested or injected into the body.
-As it travels around the body, it can be detected on the outside.

Question 31

How is nuclear radiation used to monitor kidney function?

Answer 31

-An isotope that will pass through the kidneys is used.
-If it builds up in one kidney and not the other, this could indicate that one of the kidneys is not working efficiently.

Question 32

How can nuclear radiation be used to look for blockage/damage in the intestines?

Answer 32

-If there is a blockage, then radioactivity cannot be detected after the blockage.
- If the intestines are damaged, the radioactive source can be seen to pass out of the intestines into other areas of the body.

Question 33

How is nuclear radiation used for the treatment of tumours?

Answer 33

-A tumour in the thyroid gland could be treated with radioactive iodine, which gathers in the glands and destroys nearby cells.
- A focused beam of gamma rays can be used to destroy some tumours.

Question 34

Which source would be the best tracer and why?

Answer 34

Gamma-ray because:
-They can penetrate the body and be detected on the outside.
-They are the least ionising.

Question 35

What is nuclear fission?

Answer 35

It is the splitting of a large unstable nucleus (normally uranium or plutonium).

Question 36

How does nuclear fission occur?

Answer 36

It will not normally occur it self-usually, the unstable nucleus must absorb a neutron first.

Question 37

What happens during nuclear fission?

Answer 37

The nucleus:
-Splits into two smaller nuclei of roughly equal size.
-Emits two or three neutrons, gamma rays and energy.

Question 38

What happens during nuclear fusion?

Answer 38

During fusion:
-Two light nuclei join together to form a heavier nucleus.
-Some of the mass is converted into energy and some of this energy may be emitted as radiation.
Nuclear fusion requires very high temperatures and pressures to:
-Overcome the electrostatic repulsion.
-Bring the positive nuclei close enough together for fusion to take place.

Question 39

What happens when an alpha particle is emitted?

Answer 39

-The mass number of the element is reduced by 4.
-The atomic number is reduced by 2.
This is because 2 protons and 2 neutrons are emitted from the nucleus.

Question 40

What happens when a beta particle is emitted?

Answer 40

-The mass number does not change.
-The atomic number is increased by 1.
This is because a neutron turns into a proton and an electron, and the electron is emitted as the beta particle.

Question 41

What happens when a gamma ray is emitted?

Answer 41

There is no change in mass or charge of the nucleus.

Question 42

How to write a balanced decay equation?

Answer 42

-The mass numbers on the right-hand side must add up to the same number as those on the left.
-The atomic numbers on the right must have the same total as those on the left.
Eg 219= 215 + 4 and 86= 84 +2