P4 - Atomic Structure Flashcards
What is an isotope?
Form of an element with atoms that have the same number of protons but a different number of neutrons
What was the plum pudding model?
Who created the plum pudding model?
Atoms were spheres of positive charge with tiny negative electrons stuck in them
J. J. Thomson (in 1897)
What was the alpha scattering experiment?
. Positively charged alpha particles were fired at a thin sheet of gold foil
. Most went straight through but a few scattered
What conclusions did the alpha scattering experiment lead to?
The alpha scattering experiment led to the discovery that…
. Most of an atom is empty space
. Atoms contain positively charged particles (protons) in the middle
. There is a concentrated mass in the middle - nucleus
How was it discovered that the plum pudding model is wrong?
And what was the plum pudding model replaced with?
1909 - Ernest Rutherford conducted the alpha particle scattering experiment
1911 - Ernest Rutherford created the nuclear model of the atom
What are the 4 types of radiation?
Alpha, Beta, Gamma, and neutron
What is radioactive decay?
When the nuclei of some atoms are unstable they release radiation in order to become stable.
This is a random process.
What is radiation?
Energy being transferred through waves or particles from a source.
What is nuclear radiation?
Energy being transferred through waves or particles from a nucleus.
What is ionising radiation?
Energy being transferred through waves or particles from a source, turning atoms into ions through the process.
What is alpha radiation?
A particle made of 2 protons and 2 neutrons, the same as the nucleus of a helium atom.
Represented by α.
What is beta radiation?
When a neutron splits and turns into a proton.
A high energy electron is released as a side product.
Represented by β.
What is gamma radiation?
An electromagnetic wave that gets rid of excess energy.
Represented by γ.
Why does beta decay not change an atom’s mass number?
The number of neutrons decreases by 1 and the number of proton increases by 1.
Describe alpha radiation?
- penetration power - what it is stopped by
- ionising power
- range in air
Weakly penetrating - stopped by paper
Highly ionising
Range in air: 5-6cm
Describe beta radiation?
- penetration power - what it is stopped by
- ionising power
- range in air
Moderately penetrating - stopped by a thin 2-3mm sheet of aluminium
Moderately ionising
Range in air: 1 metre
Describe gamma radiation?
- penetration power - what it is stopped by
- ionising power
- range in air
Highly penetrating - stopped by 1m concrete or thick sheet of lead
Weakly ionising
Range in air: unlimited
What is the mass and charge of alpha radiation?
Mass: 4
Charge: +2
What is the mass and charge of beta radiation?
Mass: 0
Charge: -1
What is the mass and charge of gamma radiation?
It does not have a mass or change because it is an electromagnetic wave
What is activity?
The number of radioactive nuclei that decay every second
What is activity measured in?
What device is used to measure activity?
Becquerels (bq)
1 bq = 1 nucleus decaying every second.
Geiger counter
(Geiger-müller tube)
What is half life?
The time taken for half of the radioisotope to decay
What are the two reasons we measure half life?
1- Radioactive decay is RANDOM, so we cannot tell when any particular nucleus will decay but we do know that half of them will decay in a certain time.
2- The half life is always the same for any particular radioactive isotope. Whereas the time take for ALL the radioisotopes in a sample to decay would depend on how many you had to begin with.
