# data[].attributes.body
Models of the Atom

# data[].attributes.attachment_link.readable_text
In ancient Greece, most people thought that matter was made up of combinations of four elements: earth, air, fire and water.

There were a small number of Greeks who had a different idea. They believed that if there was a piece of wood for example, it could be cut into smaller and smaller pieces until it ended up as a piece of wood that was so small it couldn't be cut anymore.

The ancient Greek philosopher Demokritos (460-370 BCE) thought that matter was made up of millions of tiny, uncuttable pieces of that same matter. In fact, the word comes from the word 'atomos', which means uncuttable.

The plum pudding model

After discovering the electron in 1897, J J Thomson proposed that the atom looked like a .

To explain the two types of static electricity, he suggested that the atom consisted of positive 'dough' with a lot of negative stuck in it. This was consistent with the evidence available at the time:

solids cannot be squashed, therefore the atoms which make them up must be solid throughout

rubbing two solids together often results in static charge so there must be something (electrons) on the outsides of atoms which can be transferred as atoms collide

# data[].attributes.attachment_link.title
Developing the atom - Models of the atom - AQA - GCSE Physics (Single Science) Revision - AQA - BBC Bitesize

# data[].attributes.attachment_link.description
In ancient Greece, most people thought that matter was made up of combinations of four elements: earth, air, fire and water. There were a small number of Greeks who had a different idea.

# data[].attributes.body
Atoms, Isotopes & Ions

# data[].attributes.attachment_link.title
Structure of the atom - Atoms, isotopes and ions - AQA - GCSE Physics (Single Science) Revision - AQA - BBC Bitesize

# data[].attributes.attachment_link.description
Learn about and revise the structure of atoms, atoms and isotopes and ions with GCSE Bitesize Physics.

# data[].attributes.body
Radioactive Decay

# data[].attributes.attachment_link.readable_text
Elements with fewer protons, such as the ones near the top of the , are stable if they have the same number of neutrons and protons. For example carbon, carbon-12 is stable and has six protons and six neutrons.

However as the number of protons increases, more neutrons are needed to keep the nucleus stable. For example lead, lead-206 has 82 protons and has 124 neutrons.

Nuclei with too many, or too few, neutrons do exist naturally but are unstable and will by emitting .

# data[].attributes.attachment_link.title
Radioactive decay - Radioactive decay - AQA - GCSE Physics (Single Science) Revision - AQA - BBC Bitesize

# data[].attributes.attachment_link.description
Elements with fewer protons, such as the ones near the top of the , are stable if they have the same number of neutrons and protons. For example carbon, carbon-12 is stable and has six protons and six neutrons. However as the number of protons increases, more neutrons are needed to keep the nucleus stable.

# data[].attributes.body
Uses & Dangers of Radiation

# data[].attributes.attachment_link.readable_text
Shining visible from a torch beam onto a hand lights the hand up because the hand has been exposed to light.

Irradiation from can damage living cells. This can be put to good use as well as being a hazard.

Irradiation for sterilisation

Irradiation can be used to preserve fruit sold in supermarkets by exposing the fruit to a source - typically cobalt-60. The emitted by the cobalt will destroy any bacteria on the fruit but will not change the fruit in any significant way. The process of irradiation does not cause the irradiated object to become radioactive.

Medical irradiation

Doctors also use radioactive sources for a number of reasons, eg:

beams of gamma rays, called a gamma knife, can be used to kill cancerous tumours deep inside the body

These beams are aimed at the tumour from many different directions to maximise the dose on the tumour but to minimise the dose on the surrounding soft tissue. This technique can damage healthy tissue, so careful calculations are done to establish the best dose - enough to kill the tumour, but not so much so that the healthy tissue is damaged.

In medical applications that involve using radioactive sources, efforts are made to ensure that irradiation does not cause any long-term effects. This is done by considering:

If the half-life chosen is too long, the damaging effects of the radiation would last for too long and the dose received would continue to rise.

Advantages and disadvantages of irradiation

Advantages

sterilisation can be done without high temperatures

it can be used to kill bacteria on things that would melt

Disadvantages

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

# data[].attributes.attachment_link.title
Irradiation - Uses and dangers of radiation - AQA - GCSE Physics (Single Science) Revision - AQA - BBC Bitesize

# data[].attributes.attachment_link.description
Shining visible from a torch beam onto a hand lights the hand up because the hand has been exposed to light. Irradiation from can damage living cells. This can be put to good use as well as being a hazard. Irradiation can be used to preserve fruit sold in supermarkets by exposing the fruit to a source - typically cobalt-60.

# data[].attributes.body
Nuclear Fission & Fusion

# data[].attributes.attachment_link.readable_text
In a , a is absorbed into a nucleus (typically uranium-235). This causes the nucleus to become uranium-236, which is violently unstable.

The entire nucleus splits into two large fragments called ' '. In addition to the 'daughter' products, two or three neutrons also explode out of the fission reaction and these can collide with other uranium nuclei to cause further fission reactions. This is known as a .

The fast moving neutrons carry most of the energy from the reaction with them (99%) but before the neutrons can collide with fresh uranium nuclei, they need to be slowed down.

This is so that the energy can pass on to other components in the nuclear reactor, which is used to heat water to drive the that turn the .

# data[].attributes.attachment_link.title
Nuclear fission - Nuclear fission and fusion - AQA - GCSE Physics (Single Science) Revision - AQA - BBC Bitesize

# data[].attributes.attachment_link.description
In a , a is absorbed into a nucleus (typically uranium-235). This causes the nucleus to become uranium-236, which is violently unstable. The entire nucleus splits into two large fragments called ' '. In addition to the 'daughter' products, two or three neutrons also explode out of the fission reaction and these can collide with other uranium nuclei to cause further fission reactions.

# data[].attributes.body
Sample Exam Questions

# data[].attributes.attachment_link.readable_text
Multiple choice questions are perhaps the easiest to complete - you simply put a cross in a box - however, the questions often have two answers that could, at first glance, be correct. Don't make the mistake of reading the first answer and thinking this is correct without checking all the others.

If it says 'Tick one box', you must tick box. If you leave it blank or tick two or more boxes you will get zero marks. These multiple-choice questions will not start with command words like 'Describe...' or 'Explain...'. They will be written in the form of a question like or

There will be more multiple choice questions on the Foundation paper.

Sample Question 1 - Foundation

When food is eaten, some of the radiation the food emits is detectable outside the body.

Which type of radiation would not be detectable outside the body?
This question is AQA material which is reproduced by permission of AQA.

Alpha particles are stopped by skin alone so would not be able to penetrate the many layers of tissue in the body.

Sample Question 2 - Foundation

The activity of a sample of potassium-40 is measured 3 times.

The measurements are given below.

Which of the following statements explains why the readings are different?
This question is AQA material which is reproduced by permission of AQA.

As radioactive decay is random, repeated measurements are unlikely to be identical.

Sample Question 3 - Higher

A nucleus is much smaller than an atom.

Approximately how many times smaller is a nucleus than an atom?
This question has been written by a Bitesize consultant as a suggestion to the type of question that may appear in an exam paper.

A nucleus is 10,000 times smaller than an atom.

# data[].attributes.attachment_link.title
Atomic structure - Multiple choice questions - Sample exam questions - AQA - GCSE Physics (Single Science) Revision - AQA - BBC Bitesize

# data[].attributes.attachment_link.description
Multiple choice questions are perhaps the easiest to complete - you simply put a cross in a box - however, the questions often have two answers that could, at first glance, be correct. Don't make the mistake of reading the first answer and thinking this is correct without checking all the others.

# data[].attributes.body
Models of the Atom

# data[].attributes.attachment_link.readable_text
In ancient Greece, most people thought that matter was made up of combinations of four elements: earth, air, fire and water.

There were a small number of Greeks who had a different idea. They believed that if there was a piece of wood for example, it could be cut into smaller and smaller pieces until it ended up as a piece of wood that was so small it couldn't be cut anymore.

The ancient Greek philosopher Demokritos (460-370 BCE) thought that matter was made up of millions of tiny, uncuttable pieces of that same matter. In fact, the word comes from the word 'atomos', which means uncuttable.

The plum pudding model

After discovering the electron in 1897, J J Thomson proposed that the atom looked like a .

To explain the two types of static electricity, he suggested that the atom consisted of positive 'dough' with a lot of negative stuck in it. This was consistent with the evidence available at the time:

solids cannot be squashed, therefore the atoms which make them up must be solid throughout

rubbing two solids together often results in static charge so there must be something (electrons) on the outsides of atoms which can be transferred as atoms collide

# data[].attributes.attachment_link.title
Developing the atom - Models of the atom - AQA - GCSE Combined Science Revision - AQA Trilogy - BBC Bitesize

# data[].attributes.attachment_link.description
In ancient Greece, most people thought that matter was made up of combinations of four elements: earth, air, fire and water. There were a small number of Greeks who had a different idea.

# data[].attributes.body
Atoms, Isotopes & Ions

# data[].attributes.attachment_link.title
Structure of the atom - Atoms, isotopes and ions - AQA - GCSE Combined Science Revision - AQA Trilogy - BBC Bitesize

# data[].attributes.attachment_link.description
Learn about and revise the structure of atoms, atoms and isotopes and ions with GCSE Bitesize Combined Science.

# data[].attributes.body
Radioactive Decay

# data[].attributes.attachment_link.readable_text
Elements with fewer protons, such as the ones near the top of the , are stable if they have the same number of neutrons and protons. For example carbon, carbon-12 is stable and has six protons and six neutrons.

However as the number of protons increases, more neutrons are needed to keep the nucleus stable. For example lead, lead-206 has 82 protons and has 124 neutrons.

Nuclei with too many, or too few, neutrons do exist naturally but are unstable and will by emitting .

# data[].attributes.attachment_link.title
Radioactive decay - Radioactive decay - AQA - GCSE Combined Science Revision - AQA Trilogy - BBC Bitesize

# data[].attributes.attachment_link.description
Elements with fewer protons, such as the ones near the top of the , are stable if they have the same number of neutrons and protons. For example carbon, carbon-12 is stable and has six protons and six neutrons. However as the number of protons increases, more neutrons are needed to keep the nucleus stable.

# data[].attributes.body
Uses & Dangers of Radiation

# data[].attributes.attachment_link.readable_text
Shining visible from a torch beam onto a hand, lights the hand up because the hand has been exposed to light.

Irradiation from can damage living cells. This can be put to good use as well as being a hazard.

Irradiation for sterilisation

Irradiation can be used to preserve fruit sold in supermarkets by exposing the fruit to a source - typically cobalt-60. The emitted by the cobalt will destroy any bacteria on the fruit but will not change the fruit in any significant way. The process of irradiation does not cause the irradiated object to become radioactive.

Advantages and disadvantages of irradiation

Advantages

sterilisation can be done without high temperatures

it can be used to kill bacteria on things that would melt

Disadvantages

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

# data[].attributes.attachment_link.title
Irradiation - Uses and dangers of radiation - AQA - GCSE Combined Science Revision - AQA Trilogy - BBC Bitesize

# data[].attributes.attachment_link.description
Shining visible from a torch beam onto a hand, lights the hand up because the hand has been exposed to light. Irradiation from can damage living cells. This can be put to good use as well as being a hazard. Irradiation can be used to preserve fruit sold in supermarkets by exposing the fruit to a source - typically cobalt-60.

# data[].attributes.body
Sample Exam Questions

# data[].attributes.attachment_link.title
Atomic structure - Multiple choice questions - Sample exam questions - AQA - GCSE Combined Science Revision - AQA Trilogy - BBC Bitesize

# data[].attributes.attachment_link.description
Learn about and revise Atomic Structure exam questions with GCSE Bitesize Combined Science