P4 - Atomic Structure Flashcards
What did John Dalton do
Said matter was made up of tiny spheres. Each element was a different atom
What did JJ Thomson do
Discovered electrons that could be removed from atoms. > spheres of positive charge with electrons in them ‘plum pudding model’
What did Rutherford do
Beam of alpha particles at thin gold foil. Some deflected but most went straight through. Some deflected as they hit the tiny nucleus - mainly empty space in atom
What did niels Bohr do
Electrons orbit at certain distances ‘energy levels’
What did James Chadwick do
Proved neutron existence > imbalance between mass and atomic number
Key information on atoms
Nucleus makes up most of mass - protons and neutrons
No overall charge as protons = electrons and cancel the charge out
Electrons can move or leave energy levels. Gain energy from EM radiation - higher level = further from nucleus
What are isotopes
Different forms of the same element
Isotopes of an element are atoms with the same number of protons but different number of neutrons
What do unstable isotopes try to do
They tend to decay into other elements. They give out radiation to become stabler (balance protons and neutrons or get rid of excess energy) ‘radioactive decay’
What do radioactive substances spit out
Spit out types of ionising radiation from nucleus - alpha beta or gamma
What is ionising radiation
Radiation that knocks electrons off, creating positive ions
Key information of alpha particles
They are helium nuclei (they’re the weird fish symbol or proportional to)
Alpha radiation is when an alpha particle is emitted from the nucleus. It is 2 neutrons and 2 electrons.
Don’t penetrate far into materials - stopped quickly
Only travel a few cm in air (absorbed by paper)
Size = strongly ionising
Beta particle key information
They are high speed electrons released from nucleus (they’re the German B for ‘ss’)
Have no mass and a charge of -1
Moderately ionising - penetrate moderately far and have a few metres in air (absorbed by aluminium sheet)
For every beta particle emitted, a neutron turns to a proton
Key information for gamma rags
They’re EM waves with a short wave length
Weird Y symbol
EM radiation released from nucleus
Penetrate far and travel long distance in air.
Weakly ionising as they pass through rather than colliding (absorbed by thick lead sheets)
What are nuclear equations
A way of showing radioactive decay
It’s written as
Atom before decay - > atom after decay + radiation emitted
What do alpha particles do if emitted
If an atom emits alpha particles, atomic number reduces by 2 mass reduces by 4 as it’s 4 He
2
Example of alpha emitted.
238 Uranium —> 284 Thorium + 4 He
92 90 2
What does beta decay do when emitted and example
Neutron turns into proton and releases a fast moving electron. Proton increased by 1. Mass stays the same 0 e
-1
14 carbon —> 14 nitrogen + 0 e
6. 7. -1
What do gamma rays do
Don’t change nucleus charge or mass. It’s a way of getting rid of excess energy from nucleus
What is half life
How quickly an unstable nuclei decay is measured using activity and half-life
What is radiation measured wi5
Geiger-Müller Tube and counter. It records count rate (amount of radiation counts per second)
Why is half life used and what is it
It is used as radioactive decay is random and you can’t predict what will decay and when
You can find out the time is takes for the amount of radiation emitted by a source to half.
Half life is used to find rate source decays (measured in becquerels Bq)
What happens each time a radioactive nucleus decays to try become stable
It’s activity decreases but never reaches 0. Use half life to see how quick activity drops
What is half life
Time taken for the number of radioactive nuclei in an isotope to half
Example of half life
Initial activity is 640 Bq Find activity as percentage after 2 half lives
640/2 = 320
320/2 = 160
(160/640)x100 = 25%
How do you plot a half life graph
Plot activity (y) against time (x) Half life found from finding time interval on - axis corresponding to halving of activity on 6 axis
Why is ionising radiation dangerous
It can enter living cells and ionise atoms within them - damage and kill cells
Chemical bonds in cells may be broken leading to mutation
What is irradiation
Exposure to radiation. Objects near a radioactive source are irradiated by it
Ways of reducing irradiation risk
Move away from substance. Lower dosage of radiation - fewer photons hit person as photons diffuse
Shield yourself - shield absorbs some radiation and decreases damage
Reduce exposure time
What is contamination
Radioactive particles getting onto objects
Dangers of contamination
Contaminated atoms might decay and radioactive particles could get into body
The substance is always giving off radiation so exposure is a long time until decontamination
What sources are the most dangerous if contaminated on outside body
Beta and gamma as they can penetrate far into the body and ionise atoms. Alpha won’t be able to penetrate far enough
Most dangerous contamination inside body
Alpha as the damage is in a localised area as alpha can’t penetrate far. Beta and gamma less dangerous as the contamination is in a larger area or passes out the body
How does a Geiger muller tube work
Radiation passes through tube and ionises gas inside it. This allows a short pulse of current to flow. The tube is attached to a sounder which counts the pulse of the current
