10/11 Physics of Atoms Year Structure Part The · 2014-08-21 · Year 10/11 The Structure of...

Year 10/11

The Structure of Physics

Part 8: Atoms & rad

ioactivity

Contents

1. Atoms 2. Atomic structure 3. Molecules & compounds 4. Radioactivity 5. Fission 6. Fusion

Key to colour code Covered in Years 7‐9 and forms the foundation of GCSE levels G to D

Ordinary text Necessary for GCSE levels D to B

Necessary for GCSE levels B to A*

Necessary for Additional Physics 3 (SC3)

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Blue text box

Purple text box

Part8:Atoms&radioactivity

Rob Gough P a g e | 1 02 November 2012

1. Atoms & elements 1.1. Atoms

Atoms & elements

Atoms are the tiny units of all matter

There are about 100 different types of atoms

These different types of atoms are called the elements

The elements are arranged in ‘families’ in the Periodic Table

Hydrogen is the lightest element. The size of atoms

Atoms are very small

The diameter of a helium atom is about 100 pm

A pm stands for picometre

A picometre is one millionth millionth of a metre.

1.2. Elements & the periodic table The Periodic Table The Periodic Table groups the elements by their properties:

Elements on the left are metals

Metals are generally shiny

Metals conduct heat and electricity

Elements on the right are non‐metals

Non‐metals are generally dull

Non‐metals do not conduct heat or electricity as well

Elements in the left‐hand column are highly reactive

Elements in the right‐hand column do not react at all.

1.3. Chemical symbols Every element has its own unique chemical symbol. Some of the more common elements (starting with the lightest) are:

H – hydrogen

He – helium

C – carbon

N – nitrogen

O – oxygen

Na – sodium

Al – aluminium

K – potassium

Fe – iron

Cu – copper

Au – gold

U – uranium.

2. Atomic structure 2.1. The nucleus

The atomic nucleus

Most of the mass of an atom is at the centre

The centre is called the nucleus

The nucleus contains protons and neutrons

Protons are heavy, positively charged particles

Neutrons are heavy particles with no charge

Surrounding the nucleus are the electrons.

Size of the nucleus

The nucleus contains nearly all the mass of an atom

The nucleus is, however, 100,000 times smaller than an atom

Most of an atom is empty space!

2.2. Protons & neutrons Protons

Protons are positively charged particles

Protons are nearly 2000 times heavier than electrons

Protons are only found in the nucleus of atoms

The number of protons in the nucleus determines the element.

Neutrons

Neutrons carry no charge

They are ‘neutral’

Neutrons are almost 2000 times heavier than electrons

Neutrons have the same mass as protons.

Stability in the nucleus

Protons on their own would try to repel each other

This is the electrostatic force of repulsion

The neutrons help to prevent this repulsion

Neutrons bring stability to the nucleus.



The mass of an atom

The electrons are so light that they can be ignored in working out the mass of an atom

The atomic mass is the number of protons + neutrons

Protons and neutrons are called ‘nucleons’ because they are in the nucleus

The atomic mass is therefore the number of nucleon.

2.3. Electrons Electrons are tiny and light

They only weigh 1/2000 of the mass of a proton or neutron

Electrons have a negative charge

They go around the nucleus, like planets around the Sun.

Electrons & the nucleus

The negative electrons are attracted to the positive protons

This is the electrostatic force

This force holds atoms together

Normally, atoms are neutral

There are equal numbers of protons (+) and electrons (‐)

The proton number determines the element

The electrons determine the chemical properties.

Electron shells

Electrons go around the nucleus

Electrons are arranged in layers like an onion

These layers are called shells. Filling shells

Each shell only holds a certain number of electrons

When the inner shell is full, the next shell starts to fill up and so on.

Electron shells in detail

Electrons are arranged in layers called shells

The inner shell can only hold a maximum of 2 electrons

When this shell is full the next shell starts to fill

This second shell can only hold a maximum of 8 electrons

The third shell also can only hold 8 electrons

The fourth shell can hold 18 electrons

The fifth and higher shells hold more electrons.

Filling up the shells

Hydrogen has 1 electron in the inner shell

Helium has 2 electrons thus filling the inner shell

Lithium has 3 electrons with 1 electron in the second shell

Beryllium has 4 electrons with 2 in the second shell.

This continues up to neon:

Neon has 10 electrons

2 in the inner shell

8 of them filling the second shell which is now full.

Next is sodium

Sodium has 11 electrons

2 in the inner shell

8 in the second shell

One is in the third shell and so on. Electron shells and chemistry

In an element the number of protons and the number of electrons are the same

The higher elements have more electrons

The chemical behavior of an element depends on the number of electrons in the outer shell.

Ions

It is very difficult to change the nucleus of an atom

It is fairly easy to add or remove electrons

An atom that has lost or gained electrons is called an ion

When electrons are removed the atom becomes a positive ion

When electrons are added the atom becomes a negative ion.



2.4. Electron shells & chemistry The periodic table in detail

Atomic number increases as you move along each row

Elements in each column have similar chemical properties

These columns are called groups

There are essentially 8 columns or groups

These groups are numbered using Roman numerals

These are Group I to Group VIII. Group I

These are the alkali metals

They have 1 electron in their outer shell

This electron is easily donated to other elements to form compounds

They are shiny, soft and highly reactive

They react violently with water

In water they produce hydroxides (alkalis) and release hydrogen.

Group II

These are the alkaline earth metals

They have 2 electrons in their outer shell

They are shiny

They are fairly reactive

They generally react with water to form alkalis

They react strongly with acids. Group III

These are called rare earth metals


This group contains the largest number of elements

They are chemically active. Group IV

Known as the carbon group

Contain 4 electrons in their outer shell

Therefore contain 4 vacancies in their outer shell

They have the ability to form complex compounds

Carbon itself is central to organic chemistry.

Group V

Also called the nitrogen group


They therefore have 3 vacancies in their outer shell

They do not readily form compounds but when formed they tend to be stable

Contains metals and non‐metals. Group VI

Sometimes called the oxygen group

Consists mainly of non‐metals

They have 6 electrons in the outer shell

They have 2 vacancies in their outer shell

Are chemically reactive

But not as reactive as group VII. Group VII

This group are called the halogens


This means they have one vacancy in their outer shell

They are highly reactive non‐metals

Fluorine is its most reactive member forming very stable compounds.

Group VIII

This group contains the noble gases


They are generally chemically inert

They do not even exist in molecular form

They are all gases at room temperature.

2.5. Atomic number & atomic mass Atomic number

The proton number determines the element

The number of protons is called the atomic number

Hydrogen is the first element (atomic number: 1)

Helium is the second element (atomic number: 2)

Lithium is the third element (atomic number: 3) and so on.



Atomic mass

Protons & neutrons are heavy

Protons & neutrons are 2000 times heavier than electrons

Nearly all of an atom’s mass is in the nucleus

Atomic mass is the number of protons + neutrons

Protons & neutrons are collectively called nucleons

Nucleons are in the nucleus

The number of nucleons gives the atomic mass of that atom.

Element symbols Every element has its own unique symbol, for example:

Hydrogen is H

Helium is He

Lithium is Li

Carbon is C

Oxygen is O, and so on. Hydrogen in detail

Normal hydrogen has 1 proton, no neutrons

The nucleon count for hydrogen is therefore 1

The proton count is also 1

The combined information for

hydrogen is 11H

The top number is the nucleon count

The bottom number is the proton count.

Helium in detail

Helium has 2 proton and 2 neutrons

The nucleon count for hydrogen is therefore 4

The proton count is 2

The combined information for

hydrogen is 42He

The top number is the nucleon count (mass number)

The bottom number is the proton count (atomic number).

Other detailed examples Potassium:

Element symbol K

Has 19 protons and 20 neutrons

Nucleon count is 39

Potassium is therefore 3919K .

Sodium:

Element symbol Na

Has 11 protons

Has 23 nucleons

Sodium is therefore 2311Na .

How many neutrons are there in sodium? Simplifying the symbols

Hydrogen has 1 proton

Any atom with one proton is hydrogen

Lithium has 3 protons

Any atom with 3 protons is lithium

Therefore, there is no need to state the element and the proton count.

Examples:

Hydrogen 1 11H H

Potassium 39 3919K K

2.6. Isotopes An isotope is an element with a

different number of neutrons

As long as the proton count does not change it is still the same element

Isotopes of an element behave the same in chemical reactions

They are, however, heavier or lighter depending on the number of neutrons.

Isotopes of hydrogen

Normal hydrogen has no neutrons so

the symbol is 11H

Some hydrogen atoms also have a

neutron so the symbol is then 21H

This is an isotope of hydrogen called deuterium

It also combines with oxygen to make water H₂O

This types of water is called ‘heavy water’

There is no problem drinking heavy water

In ordinary water about 1 in 5000 water molecules is heavy.

3. Molecules & compounds 3.1. Chemical bonds

Atomic forces, electrons & the nucleus

The forces holding electrons in atoms are electrostatic in nature

The electrons are held at certain energy levels

These energy levels are sometimes called shells

It takes energy to remove electrons from these shells

The closer the shell is to the nucleus, the more energy required to remove its electrons.



These facts are important when considering how atoms join together with what are called “chemical bonds”. Chemical bonds, forces and energy

On a simple level the bonds that hold atoms together in molecules are forces

The forces are electrostatic in nature

They involve the arrangements of negative electrons around positive nuclei

The bonds which hold molecules together in a solid or liquid are also forces.

This does not give a complete picture, however, of what is happening at the atomic level. Work (energy), force and distance are related and it is just as important to see these chemical bonds in energy terms:

It takes energy to remove electrons from an atom

It takes energy to break apart atoms in a molecule

It takes energy to overcome the forces of attraction between molecules.

Types of bonds There are 5 types of chemical bonds. In general order of strength, these are:

Ionic

Covalent

Metallic

Hydrogen bond

Van der Waals. Ionic bonds

Usually involves metallic and non‐metallic atoms

Outer electrons from the metal atoms move to the non‐metallic atom

The metal atoms become positively charged ions

The non‐metallic atoms become negatively charged ions

The outer shell of the metal ion is empty and therefore removed

The outer shell of the non‐metallic ion becomes stable full

Ionic compounds form crystalline solids which dissolve in a solvent to form ionic solutions

Ionic liquids can be formed by melting ionic compounds.

Covalent bonds

Outer electrons are shared between atoms

The idea of ‘sharing’ is, however, rather simplistic

These electrons spend some of their time in the outer shell of one atom and some time in the outer shell of the other atom

Molecular oxygen and water are examples of covalent bonds.

Ionic & covalent bonds

Most chemical bonds are considered to have both ionic and covalent characteristics

Some bonds are more ionic and some more covalent

It usually takes less energy to break covalent bonds than ionic bonds.

Metallic bonds

Outer electrons in metals are not held firmly in the outer shell

These electrons are called conduction electrons

These electrons move easily between the positive ions of the metal lattice

It is the forces between these electrons and the positive ions that create the metallic bond

Metallic bonds come in a wide range of strengths depending on the metal

The bond strength determines the melting point.

Metals have a large range of melting points (MP):

Tungsten, MP 3422 °C

Iron, MP 1538 °C

Lead, MP 327 °C

Mercury, liquid at room temperature (MP ‐39 °C).

Resulting properties of metals:

Free electrons result in high electrical and thermal conductivity

They have high tensile strength

They are ductile and malleable – the ions can be rearranged under tension or compression leading to a change of shape.



The hydrogen bond

This is the force between a hydrogen atom in one molecule and an electronegative atom in another molecule

The hydrogen atom is electropositive

The hydrogen bond is weaker than the covalent bond but stronger than van der Waals force

It is responsible for the high boiling point of water

It is also important in the structure of DNA.

Van der Waals force

This is a relatively weak force

It acts where atoms or molecules exhibit electric dipoles

A dipole has a positive side and a negative side

Dipoles line up with opposite charged sides attracted to each other

These dipoles can be natural or induced

The force increases with molecular size

This explains why small hydrocarbons have a low boiling point and large hydrocarbons have a high boiling point.

3.2. Size of atoms & molecules The size of an atom

An atom is not easily measured

Heavier atoms have more electron shells and become less well defined

A hydrogen atom is approximately 100,000 fm

1 fm = 10ˉ¹⁵ m

A hydrogen atom is therefore 10ˉ¹⁰ m = 100 pm

10 million hydrogen atoms = 1 mm. Experiment Measuring the size of an oil molecule

Prepare a 1mm drop (sphere) of oil on a thin wire

Fill a large tray with water

Sprinkle talcum powder lightly over the surface of the water

Put the oil drop in the centre of the tray

The oil expands over the water’s surface pushing the talcum powder out of the way

This continues until the oil is one molecule thick

Measure the diameter of the oil disc.

Calculation Let:

Radius of oil drop be r

Size of oil molecule be t

Radius of oil disc be R. As the volume of the oil drop is the same as the volume of the oil disc then:

⁴/₃ π × r³ = t × π×R² So: t = ⁴/₃ × r³/R² From this formula, the thickness, t, of an oil molecule can be calculated. Typically an oil molecule is 2 × 10⁻⁹ m. Estimating the size of an atom

The oil drop experiment gives the size of an oil molecule as 2 × 10⁻⁹ m

Given that an oil molecule is a long hydrocarbon chain consisting of about 12 atoms, the approximate size of an atom can be calculated:

2 × 10⁻⁹ ÷ 12 = 1.6 × 10⁻¹⁰ m = 160 pm This compares favourably with the previous estimate of the size of an atom (100 pm).

3.3. Intermolecular forces Nearly all molecules are attracted to

each other

The forces involved are electrostatic in nature

There are 2 kinds of forces called cohesion and adhesions.

Cohesion

Cohesion is the force of attraction of molecules of the same kind

These forces are electrostatic in nature

The strength of the force depends on the kind of molecule.

Example: water

Water molecules ‘stick’ to each other

There exists a cohesive force between water molecules

This is because the water molecules exhibit an electric dipole

The molecules arrange themselves to be attractive.



Adhesion

Adhesion is the force between different kinds of molecules

This force is electrostatic in nature

The strength of the force depends on the molecules involved

This is why glues for sticking things together are called ‘adhesives’.

Surface tension in liquids

Inside a liquid the cohesive force of surrounding molecules acts in all directions

At the surface the cohesive forces only act downwards and sideways

The molecules at the surface want to be closer together

This creates a ‘skin’ effect at the surface

This ‘skin’ effect is called surface tension.

Surface tension in water

This tries to pull water into a ‘blob’

This is why raindrops are round. The meniscus

The shape of the liquid surface in a container is called the meniscus.

The meniscus shape depends on:

The strength of cohesion between the liquid molecules

The strength of adhesion between the liquid molecules and the container molecules

The meniscus shape is more noticeable in a narrow container.

Example 1: water in a clean glass

Adhesion is greater than cohesion

The water prefers to stick to the glass

The meniscus is concave

This means the water curves downwards from glass.

Example 2: mercury in glass

Cohesion is greater than adhesion

The mercury prefers to stick to itself

The meniscus is convex

This means the surface curves upwards from the glass.

Example 3: water on a greasy plate

Adhesion of water with grease is low

Cohesion is greater than adhesion

The water prefers to stick to itself

The water does not stick to the greasy plate

We say the water does not ‘wet’ the plate.

Capillary action

A capillary is a narrow tube

The meniscus shape is more curved in a capillary.

If adhesion is greater than cohesion:

The liquid will climb up the tube

This is called capillary action

This is why water climbs up filter paper in chromatography.

Surfactants Surfactants are compounds that:

Reduce the cohesive forces in a liquid

Reduce the adhesive forces between different molecules.

Surfactants in washing‐up liquids

Help water to stick to the grease

Increase the ‘wetting’ to improve cleaning.

Surfactants in biology

The alveoli are small sacs in the lungs

The alveoli surface is wet to promote gaseous exchange

The water has a strong surface tension that would collapse the alveoli

Biological surfactants prevent this collapse.

4. Radioactivity 4.1. Stability in the nucleus

Neutrons and stability

Radioactivity is a property of unstable nuclei

Positive charges repel

Protons in the nucleus repel

We would expect the nucleus to fly apart

Neutrons help to make the nucleus stable

The higher the element, the more neutrons are needed for stability.



Some isotopes are unstable

If a nucleus has too many or too few neutrons it can be unstable

This means the nucleus can change into another element by emitting radiation.

4.2. Radiation Nuclear radiation There are 3 types of radiation:

Alpha particles

Beta particles

Gamma rays. Alpha particles

These are helium nuclei

They contain 2 protons (2+) and 2 neutrons

They are large and easily stopped

They only travel through about 1cm of air

They are stopped by paper or skin

Because they have 2 protons they are highly ionizing

Alpha particles are written as α⁺⁺ or

as 42He

Note: an alpha particle is NOT an atom – it has no electrons.

Beta particles

Beta particles are electrons

They are negatively charged

Because they only have one charge they are only slightly ionizing

They are very small

They will travel through 5 cm of air, paper, skin & thin aluminium

They are stopped by thick aluminium

The beta particle symbol is β⁻ or e⁻. NOTE: these electrons are being emitted from the nucleus and NOT from the electron shells surrounding the nucleus. Gamma rays

Part of the electromagnetic spectrum

High frequency, highly energetic waves

Will pass through many materials unhindered

Only stopped by thick lead and concrete

If they do hit an atom they energize electrons and cause ionization

Gamma rays are therefore also ionizing radiation.

4.3. Radiation & living things Radiation can damage living tissue

DNA and cell instructions can be damaged

Ionizing radiation can change the chemistry in the cytoplasm.

The effect of alpha particles

Alpha particles carry 2 positive charges

They will try to grab electrons from any surrounding atoms

Alpha radiation is highly ionizing

Inside a living cell this can change the chemistry.

The effect of beta particles

Beta particles are electrons

They have a single negative charge

Being small they can easily enter a cell

They increase the number of electrons in the cell

These will ionize atoms

This can disrupt the workings of the cell.

The effects of gamma radiation

Gamma rays are very energetic

They can travel right through the human body without hitting anything

If they do hit an atom they can create a cascade of excited electrons

This can seriously disrupt the workings of cells.

4.4. Detecting & measuring radiation Some workers could be exposed to high levels of radiation:

Hospital staff using X‐ray machines

Workers in the nuclear industry. Measuring activity of an isotope

Activity is the number of decays per second

This depends on the number of radioactive atoms and the half‐life

Activity is measured in Becquerels (Bq)

1 Bq = 1 decay per second. Radiation dose

Also called absorbed dose or total ionizing dose (TID)

It is measured as the energy received per unit mass

The SI unit is the Gray (Gy)

1 Gy = 1 Joule per kg of body mass



This is not a good indicator of the biological effect

More information is needed on the nature of the radiation e.g. alpha, beta or gamma.

Detectors

Photographic film badges

Geiger‐Müller tube (GM tube)

Thermoluminescent dosimeters (TLD)

Cloud chamber. Background radiation

Radioactive elements occur naturally

They are found in the air, in rocks, building materials and so on

All radiation detectors will pick up this natural radiation

It is called background radiation

To a certain extent, all living things can cope with this radiation.

4.5. Radioactivity & decay Radioactive decay If a nucleus is unstable then:

The nucleus can emit radiation

The nucleus changes into another element

This is called radioactive decay. There are 2 types of decay process:

Alpha decay

Beta decay. Alpha decay

The nucleus emits an alpha particle (helium nucleus)

The nucleus loses 2 protons & 2 neutrons.

This means:

The atomic number goes down by 2

The atomic mass goes down by 4. Beta decay

A neutron changes into a proton and

An electron is ejected from the nucleus.

0n p e

This means:

The atomic number goes up by 1

The atomic mass (nucleon count) stays the same.

Radioactive decay is a random process

We cannot predict when a radioactive atom will decay

We can measure the time for half of the atoms to decay

This time is called the half‐life

Different elements have half‐lives varying from a fraction of a second to billions of years.

Example of alpha decay Thorium decays into radium emitting an alpha particle.

Thorium isotope: 22890Th

Radium isotope: 22488Ra

228 224 490 88 2Th Ra He

Example of beta decay Potassium decays into calcium emitting a beta particle.

Potassium isotope: 4019K

Calcium isotope: 4020Ca

40 4019 20K Ca

Note that:

A neutron has changed into a proton, emitting an electron

0n p e

4.6. Half‐life The random nature of radioactivity

Radioactivity is a random process

There is no way of knowing when one atom will decay

The activity of a sample will however decrease with time

While there are a lot of radioactive atoms the decay rate is high

Once they have decayed they cannot decay again

Slowly, the activity falls. Half‐life

Half‐life is the time it takes for half of the radioactive atoms in a sample to decay

Half‐life can be measured very accurately.

Example: A radioactive source has a half‐life of 3 hours. If there are 28 g to begin with, how much is left after 9 hours?



Solution:

After 3 hours there will be 14 g left

After another 3 hours there will be 7 g left

After another 3 hours there will be 3.5 g left

Therefore, after 9 hours there will be 3.5 g. Isotope & half‐life

Half‐life is unique to each isotope

It cannot be changed by temperature or pressure or anything else

Depending on the isotope, half‐life can range from fractions of a second to billions of years.

Examples of half‐lives

Lanthanum (¹³⁸La): 10 billion years

Carbon‐14 ( 146C ): 5,700 years

Radium (²²⁶Ra): 1,600 years

Bismuth (²¹⁰Bi): 5 days.

4.7. Radioactive dating Radiocarbon dating All living things contain carbon

Normal carbon is C12 (6 protons, 6 neutrons)

C14 is a radioactive isotope

C14 has 6 protons & 8 neutrons

The half‐life of C14 is 5,700 years

Measure the C14:C12 ratio in a dead organism

This tells you how long ago it died. Uranium dating

Uranium has a half‐life of 4,500 million years

Uranium decays into lead

Measure the ratio of lead to uranium

From this we can calculate the age of the Earth.

5. Fission 5.1. Fission

Energy & mass

Albert Einstein (1879‐1955) is remembered for his theories of Special and General Relativity

The great discovery here was the relationship between mass and energy

This is encapsulated in the formula:

2E mc

Where:

Mass m has an intrinsic energy (E) within it

And c is the velocity of light. If 5 tonnes of matter could be converted into pure energy it would be enough to run the whole planet for a year. Nuclear fission

Fission means splitting apart

If an element heavier than iron can be split into lighter elements then energy is released

The usual candidate here is uranium‐235

When U‐235 is hit by a neutron it briefly comes unstable U‐236 before splitting into 2 lighter elements and releasing 3 more neutrons

These neutrons carry kinetic energy from the reaction

This kinetic energy can be turned into heat.

Fission chain reaction

In U‐235 fission, 1 neutron in leads to 3 neutrons flying out

The U‐235 atom splits into 2 smaller atoms releasing energy

If these 3 neutrons can be arranged to hit further U‐235 atoms then a chain reaction is established

Very quickly enormous amounts of energy can be released.

5.2. Nuclear bombs & power stations The atomic bomb (A‐bomb)

A critical mass of U‐235 produces fission

A chain reaction starts

An enormous amount of energy is released in a very short space of time.

Nuclear reactors

These use U‐235 to produce fission

The chain reaction is controlled so as to avoid a nuclear explosion

The heat produced is used to produce steam

The steam drives a turbine

The turbine drives a generator

The generator makes electricity.



5.3. Nuclear waste By‐products of nuclear fission

The products of nuclear fission are the lighter elements and the extra neutrons

The lighter elements are themselves radioactive

They release radiation as they decay into other radioactive elements

The half‐lives of these processes can be very long

The process continues until stable, non‐radioactive elements are created

This can take tens of thousands of years

The neutrons hit other atomic nuclei and make them radioactive

Again, a series of radioactive decays occurs

The half‐lives of these processes can be very long.

Handling nuclear waste Radioactive materials with short half‐lives:

All radioactivity produces heat

To prevent overheating these materials must be kept cool

They can be kept in special containers in ponds until radiation levels are acceptable.

Radioactive materials with long half‐lives:

Some of these materials have half‐lives of thousands if not millions on years

There is no clear idea what to do with them yet

They must be kept safe for longer than the Egyptian pyramids have been standing.

6. Fusion 6.1. Fusion in stars

Hydrogen fusion

Fusion means joining together

A star’s energy comes from the fusion of hydrogen into helium

The core of a star has sufficiently high temperature and pressure to overcome the mutual repulsion that protons (hydrogen nuclei) feel

If you compare the mass of the hydrogen nuclei before with the helium nuclei after the nuclear reaction then a small amount of mass has been ‘lost’

This lost mass has been turned into energy in the form of heat and light

This is the process of hydrogen fusion that goes on in stars.

Fusion of higher elements

Nuclear fusion doesn’t stop with making helium

Helium can be fused together to make higher elements

At each stage, energy is released

The process stops, however, with iron

Beyond iron, it takes more energy to produce the fusion

Inside normal stars the fusion stops at iron.

Creating elements beyond iron

Elements higher than iron can only be produced in a supernova

A supernova occurs when a star larger than our Sun reaches the end of its life

See Section 9: Creating the higher elements.

6.2. Artificial fusion Hydrogen fusion has been achieved outside stars. These are:

The uncontrolled fusion of hydrogen in a hydrogen bomb

Attempts at the controlled fusion of hydrogen to produce energy for electricity.

The hydrogen bomb (H‐bomb)

The H‐bomb derives its additional destructiveness from hydrogen fusion

This is achieved by first detonating an A‐bomb

Within the core of the U‐235 is a pellet of a hydrogen compound

The intense temperature and pressure of the fission reaction compresses the hydrogen until fusion takes place

This increases the energy released. Fusion power

Hydrogen fusion uses a fusion reactor

High temperature and pressure mimic the centre of a star

These conditions are needed to overcome the mutual repulsion that protons (hydrogen nuclei) feel

As helium is formed energy is released

This energy is turned into heat



The heat is used to make steam that can be used to make electricity

These devices are still in the experimental and developmental stages.

Types of fusion reactor There are 2 main types of fusion reactor that can create the high temperature and pressure for proton confinement:

Magnetic confinement

Laser confinement.

Acknowledgements I would like to thank the following people for their help and advice on the section on Chemical Bonds:

Nick Christou – Headteacher at East Barnet School, North London

Warwick Conway.

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