Physics Paper 1: Atomic Structure Flashcards
What is the radius of an atom?
1 × 10 to the power of -10 m
What does the nucleus of an atom contain?
Protons (+) and neutrons (-)
What is the overall charge of the nucleus in an atom?
Positive charge
Where are electrons found in an atom?
In energy levels which are at different distances from the nucleus
What happens with energy levels in an atom?
Energy levels further away from the nucleus are at a higher energy than those closer to the nucleus
What happens when an atom absorbs electromagnetic radiation?
An electron can move from a lower energy level to a higher energy level
What happens if an atom emits electromagnetic radiation?
The electron returns to a lower energy level
What does the atomic number tell us about an atom?
The number of protons (and electrons)
What does the mass number tell us about an atom?
Number of protons + neutrons
Why do atoms have no overall charge?
Because the number of positive protons is equal to the number of negative electrons, so they cancel each other out so the atom is neutral overall
How do we find the amount of neutrons in an atom?
Subtract the atomic number from the mass number
What is an isotope?
Atoms of the same element with different numbers of neutrons
What is an ion?
An atom that has gained or lost one or more electron
What did the Ancient Greeks believe?
They believed everything is made of atoms and atoms are tiny spheres which can’t be divided
What was discovered in 1897?
Scientists discovered that atoms contain tiny negative particle (electrons), atoms are not tiny spheres that cannot be divided, they must have an internal structure
What is the plum pudding model?
An atom is a ball of positively charged particles with electrons embedded in it
Describe the alpha scattering experiment
1) first tool a piece of gold foil- gold is useful because it can be hammered out into thin foil
2)fired alpha particles at gold foil
3)most alpha particles passed straight through the gold foil without changing direction
4)some particles got deflected and went different directions and others completely bounced off it
What were the results of the alpha scattering experiment?
1)most went straight through-atoms are mostly empty space- plum pudding model was wrong
2)Some alpha particles deflected means centre of atom must have a positive charge that repelled alpha particles
3)because some bounced straight back this mean the mass of the atom must be concentrated in the centre (nucleus)
What did the scientists swap the plum pudding model with because of the alpha scattering experiment?
The nuclear model
What did Niels Bohr discover?
.electrons orbit the nucleus at specific distances
.called orbits energy levels
What did James Chadwick discover?
The nucleus also contains neutrons
What do some isotopes have?
An unstable nucleus
How do isotopes with an unstable nucleus become stable again?
The nucleus gives out radiation, this is called radioactive decay
True or false: radioactive decay is a random process?
True
What is activity?
The rate at which a source of unstable nuclei decay
What is activity measured in?
Becquerel (Bq)
How is activity measured?
Using a Geiger-Muller tube
What is count rate?
Number of decays per second
What does alpha radiation consist of?
2 protons and 2 neutrons (same as helium nucleus)
What does beta radiation consist of?
A high speed electron
What does gamma radiation consist of?
Electromagnetic radiation
What is the penetrating power of Alpha decay?
Travels around 5cm
What is the penetrating power of beta decay?
Travels around 15cm
What is the penetrating power of gamma?
Travels several meters
What is alpha stopped by?
Paper
What is beta stopped by?
Aluminium
What is gamma stopped by?
Lead
How ionising is alpha?
Very strongly ionising
How ionising is beta?
Quite strongly ionising
How ionising is gamma?
Weakly ionising
What happens during alpha decay?
Atomic number decreases by 2, mass number decreases by 4
What happens during beta decay?
Atomic number increases by 1, mass number does not change
What happens during gamma decay?
Atomic number + mass number stay the same
What is half life?
.The time it takes for the number of nuclei of the isotope in a sample to halve
.half life can also be the time it takes for the count rate (activity) from a sample containing the isotope to fall by half
How can ionising radiation be dangerous?
It can increase the risk of cancer in humans
What is irradiation?
Exposing an object to nuclear radiation
What is irradiation used for?
.to sterilise- usually done by heating
Why does an object not become radioactive when it is irradiated?
Because the object only cones in contact with the radiation and not the radio active atom
What are some protection methods?
.gloves protect against alpha
.beta and gamma reduced using a lead apron
.Shielding
.limiting time near radiation
.monitoring
What is contamination?
When unwanted radioactive isotopes end up on other materials
Why is contamination hazardous?
Because radioactive atoms decay and emit ionising radiation
How hazardous is alpha radiation to humans?
Strongly ionising, but easily stopped by dead skin cells, but dangerous is inhaled or swallowed
House hazardous is beta to humans?
Quite ionising and can penetrate into the body
How hazardous is gamma radiation to humans?
Weakly ionising, can penetrate into the body but likely to pass straight through
Why do scientist peer review)
To check there was no false claims
