FULL TOPIC 4: ATOMIC STRUCTURE

Who was the first person to discover the atom?

Democritus (5th century BC)

In 1804 who agreed with Democritus?

John Dalton, matter was made up of tiny spheres that couldn't be broken up - each element was made up of a different type of atom

What did JJ Thomson discover?

electrons

When did J.J. Thomson discover the electron?

1897

What kind of model did JJ Thomson suggest?

atoms were spheres of positive with tiny negative electrons stuck in them (plum pudding model)

When did Rutherford attempt the alpha scattering experiment?

1909

What did Rutherford discover?

Nucleus (gold foil) and protons (after Neils Bohr)

What is the alpha scattering experiment?

Rutherford set up an experiment where he fired a beam of positive alpha particles towards some thin gold foil. He found most of the particles went straight through the foil. This suggested that there was lots of empty space, however he noticed that some alpha particles were deflected, with a few by more than 90 degrees. = concentrated positive nucleus in the centre of the atom since two positive forces repel.

What was Rutherfords nuclear model?

A compact nucleus (fully positive) with a cloud of negative charge - the atom should collapse

When did Niels Bohr make his discovery?

1913

What did Niels Bohr discover?

Electrons orbit the nucleus, held in shells = prevents the atom from collapsing

What did James Chadwick discover?

Neutrons in the nucleus

What is the radius of an atom?

1 x 10^-10 metres = 0.1 nanometers

What is the radius of a nucleus?

1x10^-14 metres

Isotope

Atoms of the same element that have different numbers of neutrons

Which types of iodising radiation are spat out during radioactive decay

alpha, beta, gamma radiation (may release neutrons)

What is an alpha particle?

2 proton and 2 neutrons (helium nucleus)

How penetrating are alpha particles?

Not very penetrating; they only travel a few centimeters in air.

Why are alpha particles highly ionising?

They are highly ionising due to their size.

What can absorb alpha particles?

Alpha particles are absorbed by paper.

What is a beta particle?

A fast moving electron (no mass) (charge of -1)

How penetrating are beta particles?

Moderately penetrating, have a range of a few metres in the air

How ionising are beta particles?

Moderately ionising (less than alpha, more than gamma)

What can absorb beta particles?

A sheet of aluminium (around 5mm)

What happens to the nucleus when a beta particle is emitted?

A neutron turns into a proton as the negative charge has left it

What are gamma rays?

Waves of electromagnetic radiation released by the nucleus

What can absorb gamma rays?

Thick sheets of lead or meters of concrete

Why are gamma rays weakly ionising?

Tend to pass through each other rather than collide with atoms

How penetrating are gamma rays?

They penetrate far into materials without being stopped and will travel a long distance through air.

When an unstable nucleus emits an alpha particle what happens?

lose 2 protons 2 neutrons (subtract 4 from mass and 2 from atomic number)

When an unstable nucleus emits a beta particle what happens?

gains a proton (add one to the atomic number)

Equation for neutron emission?

subtract 1 from mass

What do we measure activity in?

Becquerels (Bq), 1 Bq = 1 decay per second

Half life

Time taken for the no. of radioactive nuclei to half in a sample

Where does background radiation come from?

Natural sources such as rocks and cosmic rays from space.

Man-made sources such as the fallout from nuclear weapons testing and nuclear accidents.

What are radiation doses measured in?

Sieverts (Sv) or millisieverts (mSv)

How are nuclear radiation used in medicine?

Exploration of internal organs

control or destruction of unwanted tissue.

Why do we use gamma radiation for medical tracers?

They are less harmful than alpha or beta radiation - want to use isotopes with the shortest half life as possible, emit radiation for a short period of time

How does ionising radiation (beta particles) help in medicines?

Radiotherapy

What does radiation sickness cause?

Vomiting, tiredness, hairloss

Irradiation

The process by which objects are exposed to radiation

What determines how harmful radiation is?

1. type of radiation

2. where your'e exposed to it

3. the amount

What types of radiation are ionising?

alpha, beta, gamma, and X-ray

Why is ionising radiation so dangerous?

They enter living cells and interact with the molecules (ionising DNA - causes mutations = cancer)

What are some non ionising radiation?

UV rays, visible light, infra-red, microwave, and radiowave

which non ionising radiation is still dangerous?

UV rays - cause skin cancer

What precautions can we take when handling radiation?

wearing gloves, overalls, using tongs, keeping item in a lead lined box

Nuclear fission

the splitting of a large and unstable nucleus

Spontaneous fission is rare, for the fission to occur it needs to_

first absorb a neutron

How does nuclear fission work?

1. The unstable nucleus undergoing nuclear fission splits into 2 smaller nuclei.

2. It also emits 2 or three more neutrons + gamma rays

3. Chain reaction

What is an explosion caused by a nuclear weapon caused by?

Uncontrolled chain reaction

How do we control the rate of fission?

Control rods that are lowered into the reactor to absorb neutrons - slows down reactions

What do we use the energy from nuclear fission for whilst the control rods are in action?

The energy produced is used to heat up water, the steam is then used to drive the turbines which generates electricity.

What is nuclear fusion?

The joining of two light nuclei to form a heavier nucleus.

What happens to some of the mass during nuclear fusion?

Some of the mass may be converted into the energy of radiation.

Pros of nuclear fusion?

Pros: abundant source of energy, no pollution, no risk of meltdowns

Cons of nuclear fusion?

Only happens at really high temperatures

Pros of nuclear fission?

Uranium or plutonium is relatively cheap + produces large and steady amount of energy

Doesn't produce greenhouse gases

Cons of nuclear fission?

Very expensive to build

Nuclear waste is expensive to get rid of - buried underground in special bunkers

Risk of major disaster if malfunctions

Superstitions people don't like nuclear energy (scared)