Atomic structure

Question 1

Define the term proton

Answer 1

A positively charged particle found in the nucleus of an atom

Question 2

Define the term neutron

Answer 2

A neutral particle found in the nucleus of an atom

Question 3

Define the term electron

Answer 3

A negatively charged particle that orbits the nucleus of an atom.

Question 4

Define the term atom

Answer 4

The smallest unit of an element, contains neutron(s) and proton(s) in the nucleus and electron(s) in outer shells. It always has a neutral charge

Question 5

Define the term ion

Answer 5

An ion will be positive when an electron is removed from an atom or negative if an electron is added

Question 6

Define the term atomic number

Answer 6

The atomic number tells us how many protons there are in an atom, it is sometimes called the Z number. It defines an elements postion on the periodic table

Question 7

Define the term mass number

Answer 7

The mass number tells us the total of protons and neutrons in an atom it is sometimes called the A number

Question 8

Define the term element

Answer 8

A substance which is made from only one type of atom

Question 9

Define the term compound

Answer 9

A substance which is made from more than one type of atom.

Question 10

Some elements have different isotopes, what does this mean?

Answer 10

The name of an element is defined by its atomic number ie the number of protons in the nucleus but some elements have different numbers of neutrons and therefore different mass numbers, they are called isotope of the element.
Eg Sodium has two isotopes Na23 and Na 24, both have 11 protons but one has 12 neutrons and the other 13.

Question 11

Who first suggested the idea of atoms

Answer 11

Democritus a Greek philosopher (460-370BC)

Question 12

Who discovered that electrons were emitted from the surface of hot metal and when was it.

Answer 12

J J Thompson in 1897, he showed that they were negatively charged and less massive than an atom.

Question 13

What model did J J Thompson suggest for the atom.

Answer 13

The plum pudding model with electrons dotted around inside a positively charged sphere

Question 14

What is an alpha particle?

Answer 14

It is a positively charged helium ion He2+

Question 15

Describe the gold foil experiment carried out by Geiger and Marsden in 1909

Answer 15

They directed a beam of alpha (He2+) particles which travel very quickly through a thin sheet of gold . They expected all of the particles to pass through but a small number were deflected and bounced back.

Question 16

How did Rutherford explain the results of the gold foil experiment

Answer 16

He suggested that the deflection of the alpha particle was due to an electrostatic charge between the particle and a very small charged nucleus, he also said the nucleus could be massive.. He said that the nucleus may be either positively or negatively charged. A positive charged nucleus would deflect the positively charged alpha particle away whereas a negatively charged one would pull the particle toward and around it.

Question 17

How is the gold foil experiment explained nowadays.

Answer 17

The diameter of the nucleus of an atom is tiny in comparison to the atom 1:20000. The nucleus is positively charged. Most of the alpha particles pass through the gold atom. A few hit the nucleus and were deflected back as the positive charges repelled each other. Some came near the nucleus and were deflected slightly. .

Question 18

Who discovered that there are neutrons in the nucleus of an atom.

Answer 18

James Chadwick 1932

Question 19

Describe the model of the atom suggested by Neils Bohr in 1913

Answer 19

He suggested that electrons orbit the nucleus at specific distances.

Question 20

Explain the positive and negative points of Bohr’s 1913 explanation of the model of the nucleus

Answer 20

Positive
1. It explains why hydrogen emits particular wavelengths of electromagnetic radiation
Negative
It does not allow a full explanation of the behaviour of atoms in larger atoms

Question 21

Describe the discovery of radioactivity

Answer 21

1. Discovered by Henry Becquerel
2. In 1898
3. He left uranium salts next to a photographic plate which was sealed into a black bag.
4. When the plate was developed it had been affected as if it had been exposed to light.
5. He realised that particles had been emitted from the uranium salts and passed through the bag.

Question 22

Describe nuclear decay

Answer 22

Most atoms have stable nuclei, some however do not and throw out particles to make themselves more stable. It is a random process and it not affected by other factors such as temperature and chemical reactions. Radium is one element which does this. The name for it is radioactivity.

Question 23

Identify the four types of radioactive emission.

Answer 23

1. Alpha particles
2. Beta particles
3. Electromagnetic waves (gamma rays)
4. Neutrons

Question 24

Explain the term alpha decay

Answer 24

An alpha particle consists of 2 protons and 2 neutrons. When an alpha particle is emitted from a nucleus it causes the nucleus to change into another with a mass number of 4 less and an atomic number 2 less.

Question 25

Explain what a beta particle is and what happens to an element when one is emitted from it’s nucleus

Answer 25

A beta particle is a fast moving electron.
When a beta particle is emitted from a nucleus a neutron turns into a proton. The mass number of the element remains the same but the atomic number increases by 1

Question 26

Describe a gamma ray

Answer 26

A gamma ray is an electromagnetic wave, they are sometimes given out with either an alpha or beta particle. They do not have any mass or charge and therefore do not affect the mass number or atomic number of the element. They do carry energy away from the nucleus which makes the nucleus more stable.

Question 27

Describe what happens when a neutron is emitted from a nucleus during radiation

Answer 27

This is a rare but dangerous occurrence, some very unstable nuclei can emit a neutron causing the mass number to reduce by one, the atomic number remains the same.

Question 28

How does radiation damage body tissues?

Answer 28

All types of radiation cause ionisation. The ions which are made in the body damage the body tissues.

Question 29

Describe an experiment to show the ionising effect of radium .

Answer 29

1. On a gold leaf electroscope the gold leaf is repelled from the positively charged metal stem and so sticks out.
2. When the radium source is brought near the electroscope the leaf falls.
3. The alpha particles from the radium create +ve and -ve ions in the air above the electroscope.
   4, The +ve ions are repelled from the electroscope and the -ve ones are attracted.
   The negative ions neutralise the metal stem so the gold leaf is no longer repelled.

Question 30

Describe the properties of radiation in regards to alpha, beta and gamma particles

Answer 30

1. Alpha particles travel about 5cm through air but can be stopped by a piece of paper. They ionise air very strongly.
   2, Beta particles can travel several metres through air, they can be stopped by a sheet of aluminium a few cm thick. They ionise air but not as strongly as alpha particles.
2. Gamma rays can travel huge distances through air, they can only be stopped by a thick sheet of lead. They only ionise the air weakly.

Question 31

What is the name of the tube used to detect ionising radiation.

Answer 31

A Geiger Muller tube

Question 32

Describe radioactive decay in radioactive materials

Answer 32

The atoms of some radioactive materials emit alpha, beta or gamma radiations from their nuclei. It is however a random process, it is not possible to predict when a nucleus will decay.

Question 33

Explain the term half life

Answer 33

It is the time taken for half of the nuclei in a radioactive sample to decay. Every type of radioactive material has a different half life. It has the symbol t1/2

Question 34

What is the count rate of a radioactive source?

Answer 34

It is used when measuring the number of particles emitted per second in a GM tube

Question 35

What is a Bequerel?

Answer 35

The unit used to describe the number of particles emitted from a radioactive source in 1 second.
(Bq)

Question 36

Describe the term half life

Answer 36

It is the time taken for the number of nuclei in a radioactive isotope to halve.
In a half life the count rate or activity of the radioactive sample also halves.

Question 37

Explain the effects of radiation damage in the body

Answer 37

1. Radiation damage is caused by ionisation which creates chemicals, these can destroy human cells.
2. Alpha particles cause the most damage as they ionise the most, however they do not travel very far so are less dangerous than gamma rays.
3. Although gamma rays cause less ionisation they can penetrate the body from several metres away.
4. Moderate exposure to radiation can cause cancers and birth defects. High doses of radiation are likely to be fatal.

Question 38

What is irradiation?

Answer 38

The process of exposing an object to nuclear radiation without the object becoming radioactive

Question 39

What is meant by the term radioactive contamination?

Answer 39

When radioactive isotopes get into places where we do not want them it is called contamination. This happened after the nuclear disasters in Chernobyl and Fukushima