P1 - Atomic structure Flashcards
What did Democritus think about the model of the atom?
He thought all matter was made up of identical lumps called atomos.
When Democritus come up with his atom model theory?
5th century BC Greece
What did John Dalton think about the model of the atom?
That matter was made up of atoms that couldn’t be broken up, and that each element was made up of a different type of atom.
When did John Dalton come up with his atom model theory?
1804
What did J.J. Thomson think about the model of the atom?
He discovered particles called electrons that could be removed from atoms. He suggested that atoms where spheres of positive charge with negative electrons embedded in them, it was called the plum pudding model.
When did J.J. Thomson come up with the plum pudding model?
1904
What was the Alpha scattering experiment?
They fired a beam of alpha particles at thin gold foil. Based on the plum pudding model they expected the particles to pass straight through the gold sheet or be slightly deflected. Some particles did go straight through the sheet but some where deflected more than than expected and a few were deflected back the way they had come.
What did Ernest Rutherford and his students think about the model of the atom?
Because a few alpha particles were deflected back they realised most of the mass of the atom must be concentrated at the centre in a tiny nucleus. This nucleus must also have positive charge as it repelled the positive alpha particles. As nearly all passed through, most of the atom is empty space. They had discovered the first nuclear model of the atom.
When did Rutherford conduct the alpha scattering experiment?
1909
What was the nuclear model that developed from the alpha scattering experiment?
A positively charged nucleus surrounded by a cloud of negative electrons.
What did Niels Bohr say about the atom model?
Electrons orbiting the nucleus do so at certain distances called energy levels. Futher experiments caused him to change it to a nucleus made up of a group of protons.
When did Niels Bohr make his discoveries?
Early 1900 after Rutherford
What did James Chadwick do?
Proved the existence of the neutron which explained the imbalance between the atomic and mass numbers.
When did James Chadwick discover the neutron?
1932
Current model of the atom
In book
What is an isotope?
atoms with the same number of protons (atomic number) but a different number of neutrons (different mass number)
Outline the process of radioactive decay
Unstable isotopes tend to decay into other elements and give out radiation as they try to become more stable
Name the three types of ionising radiation
gamma γ
alpha α
beta β
Where does ionising radiation come from?
Radioactive substances emit it from their nucleus
Other than radiation, what do radioactive substances emit?
Neutrons (when they decay) as they balance their atomic and mass numbers
What does ionisng radiation do?
It knocks electrons off atoms, creating positive ions. Ionising power of a radiation source is how easy it is to do this.
What are alpha particles?
Helium nuclei
What is alpha radiation?
When an alpha particle is emitted from the nucleus
What is an alpha particle made up of?
Two neutrons and two protons
Which radiations are the most, moderate, least penetrating?
Gamma most
Beta moderate
Alpha least
Which radiations are the most, moderate, least penetrating?
Alpha most
Beta moderate
Gamma least
How far does alpha penetrate and what stops it?
Not far, stopped quickly.
Only travel a few cm in air, and are absorbed by a sheet of paper.
What is alpha radiation used for?
Smoke detectors, ionises air particles causing a current to flow then if there is smoke in the air it binds to the ions, stopping the current and sounding the alarm.
What are beta particles?
High speed electrons
A fast moving electron released by the nucleus
What is the mass and charge of a beta particle?
Virtually no mass
Charge of -1
How far does beta penetrate and what stops it?
Penetrates moderately far, before colliding
Range in air of few metres, absorbed by sheet of aluminium (around 5 mm)
For every beta particle emitted, a neutron in the nucleus has….
Turned into a proton
What are beta particles used for?
Beta emitters are used to test the thickness of sheets of metal, as the particles are not immediately absorbed and dont penetrate too far.
What are gamma rays?
EM waves with a short wavelength
Waves of electromagnetic radiation released by the nucleus
How far does gamma penetrate and what stops it?
Far into materials without being stopped, travel a long distance through air.
Absorbed by thick sheets of lead or metres of concrete.
Why are gamma rays weakly ionising?
They tend to pass through rather then collide with atoms, eventually they hit something and do damage.
What do nuclear equations show?
Radioactive decay using element symbols
How are nuclear equations written?
atom before decay -> atom after decay + radiation emitted
What is the main rule of nuclear equations?
The total mass and atomic numbers must be equal on both sides
Mass and atomic numbers have to balance
What does alpha decay do to the nucleus?
Decreases the charge and mass
When an atom emits an alpha particle (alpha decay) what happens to the atomic and mass numbers?
Its atomic number reduces by two
Its mass number reduces by four
What can an alpha particle be written as in nuclear equations?
A helium nucleus
Symbol He
Top 4
Bottom 2
What does beta decay do to the nucleus?
Increases the charge, mass stays the same
What happens during beta decay?
A neutron in the nucleus turns into a proton and releases a fast moving electron (beta particle)
What does the number of protons increase by during beta decay?
1
How is a beta particle written in nuclear equations
Symbol e
Top 0
Bottom -1
What do gamma rays do to the charge and mass of the nucleus?
Nothing, they get rid of excess energy from the nucleus
What do half life and activity measure?
How quickly unstable nuclei decay
What can radiation given out from the nuclei be measure with?
A Geiger Muller tube and counter which records the count rate
What does count rate mean?
The number of decays recorded each second
What is half life?
The time taken for the number of radioactive nuclei in an isotope to halve
And the time taken for the activity and count rate to halve
What is activity?
The rate at which a source decays
What is activity measured in?
Becquerels
Bq
1 Bq is 1 decay per second
Older radioactive sources emit….
less radiation, each time the nucleus decays to become stable the activity as a whole will decrease
What does a short halve life mean?
The activity falls quickly because the nuclei are very unstable and rapidly decay
How do you measure half life with a graph?
Plot a graph of activity (y) against time (x)
The half life is found by halving the activity then drawing a line along till it reaches the line, then draw down and repeat halving it again till you cant anymore.
What is background radiation?
Low level radiation around all the time
What is exposure to radiation called?
Irradiation
Does irradiation make something radioactive?
No
How can you reduce the effects of irradiation?
Keep sources in lead lined boxes
Stand behind barriers
Use remote controlled arms from a different room
What is it called when unwanted radioactive atoms get into or onto an object?
Contamination
What are ways to prevent contamination?
Gloves and tongs
Protective suits
What radiations are most dangerous outside the body (irradiation) and why?
Beta and gamma as they can penetrate and get into organs, whilst alpha cannot penetrate the skin
What radiation is most dangerous inside the body (contamination) and why?
Alpha as they do damage in a very localised area, whilst beta sources are absorbed over a wide area and some passes out, gamma passes straight out (least ionising)
Describe 3 risks of radiation?
- Can enter living cells and ionise atoms and molecules within them, leading to tissue damage
- Lower doses cause minor damage to cells that causes cell mutation called cancer
- Higher doses kill cells completely causing radiation sickness, vomiting, tiredness, hair loss
What is gamma medically used for?
Medical tracers
Radiotherapy
How do gamma medical tracers work?
Radioactive isotopes are injected or swallowed by people and their progress around the body is followed with an external detector, used to see if thyroid is taking in iodine
Why is gamma used for medical tracers?
Because it passes out of the body with little ionisation and has a short half life
How is gamma used for radiotherapy?
Rays are directed with a specific dosage to kill cancer cells
How is beta used to treat cancer?
Beta emitters or other radiation emitting implants can be put next to or inside tumours
What is nuclear fission?
The splitting of a large, unstable nucleus into two smaller, daughter nuclei
What is nuclear fusion?
The joining or fusion of two smaller nuclei to form a larger and heavier nucleus
What is released during nuclear fission?
Two or three neutrons and energy
What is released during nuclear fusion?
A lot of energy
