Atomic Structure and radiation Flashcards
What is the nuclear model of the atom
The nucleus makes up most of the atom’s mass
It contains positively charged protons and neutrally charged neutrons
Overall positive charge
The rest of the atom is mostly empty space
Negative electrons circulate around outside nucleus giving the atom its overall size
How big is the nucleus compared to the whole atom
Radius of nucleus is 10,000 times smaller than the radius of the atom
What are relative charges and masses of the particles
Proton mass = 1 charge =+1
Neutron = 1 charge = 0
Electrons = 1/2000 charge =-1
Key rules of atoms
1 no overall charge
2 charge of an electron is same size as charge of proton but opposite
3 so number of protons = number of electrons
4 adding or removing electron makes atom charged particle called ion
What are isotopes
Atoms of an element with the same number of protons but different number of neutrons
So same atomic number but different mass numbers
Most elements have isotopes but usually one or two stable ones
Other unstable ones are radioactive and decay into other elements giving out radiation
What are unstable isotopes
Most elements have isotopes but usually one or two isotopes
Other isotopes tend to be radioactive so they decay into other elements and give out radiation
Three types of radiation- alpha, beta, gamma
What happens with unstable isotopes with atomic number over 83
With atomic numbers above 83
Often decay by losing an alpha particle
Include radium, uranium, plutonium
What happens to isotopes with atomic number less than 83
They tend to undergo beta decay
What are alpha particles
A particle consisting of 2 protons, 2 neutrons and a helium nucleus
Relative mass 4 and charge +2
Relatively big, heavy and slow moving
Don’t penetrate very far and stop quickly when travelling in air
They are strongly ionising because they collide into many atoms dislodging electrons
What are beta particles
An electron created and emitted from nucleus
When a neutron changes to proton a beta particle is emitted
Charge -1 mass of 0
They penetrate moderately, have long range and moderately ionise
What are gamma particles
Radiation emitted by unstable nuclei after alpha or beta emission
Electromagnetic wave
no mass and no charge
Doesn’t change the number of protons and neutrons
Ionise weakly
Travel far and pass through glass paper and aluminium
What is neutron emission
Neutrons are emitted by some atoms due to alpha particles colliding with unstable nuclei
This cause ps neutrons to be emitted from the nucleus
What are sources of background radiation
10% Cosmic radiation 51% Air by way of Radon gas from rock radiation 12% Food 12% medical xrays 14% rocks and building materials 1% nuclear industry
Also man made eg nuclear weapons tests or accidents or waste
What is an example of non natural background radiation
Nuclear power station
Nuclear weapon testing
Nuclear accidents eg Chernobyl
What safety protection would the teacher use to handle and store radioactive samples
Keep as far away as possible from source of radiation so
Use long handled tools - avoid skin contact
Keep source pointing away
Spend little time as possible in at risk areas
Stay behind concrete barriers or using lead plates
Store in lead box - put away immediately
If regular contact use lead apron and face masks
Patients having radiotherapy expose little of body as possible
Why is a radioactive tracer used in the body
patient drinks liquid with small amount radioactive substance
liquid flows in and out kidney so reading goes up and down
blocked kidney shows reading up and stays up
iodine is used -half life of 8 days so quickly becomes stable
Gamma radiation can be detected outside the body
Half life is long enough for the test to be carried out
Why do scientists use journals to share their findings
1 it becomes part of the scientific record
2other scientists can develop their work
3 it must be peer reviewed before it can be published
What is the process when a nucleus of an atom is struck by a neutron causing the nucleus to split into smaller fragments
A fission reaction
What is the process when 2 small nuclei are fused together to form single larger nucleus
A fusion reaction
What did Ernest Rutherford discover
Alpha radiation @ - stopped by paper
Beta radiation B - passes through paper
Gamma radiation Y - more penetrating than beta
Radioactive substances have unstable nucleus
Become stable by emitting alpha beta and gamma radiation
An unstable nucleus decays when it emits radiation
Radioactive decay is random event
What is background radiation- examples
In the environment- air , ground, in buildings
Space - cosmic rays
Devices - X-ray
What is the difference between plum pudding model and nuclear Rutherford model
1 nuclear model shows mass concentrated at centre/ nucleus.
Pp model shows mass evenly distributed
2 nuclear model - positive charge occupies only small part of atom.
Ppm - positive charge spread throughout atom
3 nm - electrons orbit some distance from centre of nucleus
Ppm- electrons embedded in mass of charge
4 nm - atom mostly empty space
Ppm - solid mass
Why did Rutherford s show plum pudding was incorrect
Plum pudding model could not explain findings of some alpha particles deflecting backwards away from and some passing through thin foil
Fire positive alpha particles at thin gold sheet
100000 measurements
Very small number of alphas deflect backwards
Why
Nucleus must be positive to deflect or repel alphas
Nucleus v small so few alphas deflect backwards
What happens when alpha particles hit thin gold foil
1 most alpha particles pass straight through
2 the number deflected decreases as deflection angle deflection increases
Because - gold foil nucleus at centre has positive charge so repels alphas
- nucleus much smaller than the atom
- much empty space to pass through
how do we represent an element
atomic number =number of protons
mass number = number of protons and neutrons
neutral atom - number of protons=number of electrons
radioactive dating
carbon dating
uranium dating
