Atomic Structure Flashcards
what was John Dalton’s model of the atom?
solid sphere model
how was the solid sphere model of the atom useful?
recognised atoms of a particular element differ from other elements
how was the solid sphere model of the atom wrong?
said atoms were indivisible
what was JJ Thomson’s model of the atom?
plum pudding model
describe the plum pudding model of the atom
a sphere of uniform positive charge with negative charges embedded in it to create an overall neutral charge
how was the plum pudding model of the atom correct?
recognised electrons
how was the plum pudding model of the atom wrong?
no nucleus
what was Rutherford’s model of the atom?
nuclear model
describe the nuclear model of the atom
small, positively-charged nucleus surrounded by empty space and then a layer of electrons to form the outside of the atom.
how was the nuclear model of the atom correct?
realised positive charge was localised in nucleus of atom
how was the nuclear model of the atom wrong?
didn’t explain why electrons remain in orbit around nucleus
what was Bohr’s model of the atom?
planetary model
describe the planetary model of the atom
- built on the nuclear
- suggested the electrons orbited the nucleus in different energy levels or specific distances from the nucleus.
- When atoms absorb energy, the electrons at a particular level are pushed up to higher levels (at bigger distances from the nucleus). In time, they jump back down to a lower level releasing light of definite frequencies.
how was the planetary model of the atom correct?
proposed stable electron orbits
how was the planetary model of the atom wrong?
model didnt work well for heavier atoms
what is the relative charge and mass of a proton?
+1 and 1
what is the relative charge and mass of a neutron?
0 and 1
what is the relative charge and mass of an electron?
-1 and negligible
what is the diameter of an atom?
1 x 10^-10 m
how can electrons move to higher energy levels?
if they gain energy
how can electrons gain energy?
by absorbing light or other EM radiation
what are unstable nuclei?
- when the ratio of protons and neutrons is unstable
- emit radioactivity to try to become stable
what are the 4 types of nuclear radiation?
- alpha
- beta
- gamma
- neutron
describe alpha radiation
- structure: 2 protons, 2 neutrons
- relative charge: +2
- relative mass: 4
- ionising power: high
- penetration: low; stopped bypaper
describe beta radiation
- structure: fast moving electron
- relative charge: -1
- relative mass: negligible
- ionising power: medium
- penetration: medium: stopped by few mm of aluminium
what is the beta decay equation?
n –> p^+ + e^-
what is half-life?
- the time taken for the number of radioactive nuclei to reduce by a half
- the time taken for activity to reduce by a half
describe gamma radiation
- structure: high frequency, electromagnetic wave
- relative charge: 0
- relative mass: 0
- ionising power: low
- penetration: high; slowed by lead and concrete
what is radiation exposure measured in?
- sieverts and millisieverts
- 1000 mSv = 1 Sv
how many mSv is 1Sv?
1000 mSv
what must you do, to measure the radioactivity of an object?
subtract background radiation
what is the most dangerous type of radiation, outside the body?
- alpha is the least dangerous as it is the least likely to be able to penetrate the body
- beta and gamma are more dangerous.
what is the most dangerous type of radiation, inside the body?
- if inhaled or ingested, alpha is the most dangerous as it is all absorbed by the part of the body which surrounds it.
- Gamma is the least dangerous as it can escape.
what does it mean if something is contaminated?
a radioactive material is on or in something and the thing is therefore radioactive (inhale, ingest, become covered in)
what does it mean to be irradiated?
exposed to ionising radiation - not radioactive itself
what are some uses of radiation?
- smoke detectors
- measuring thickness of materials
- finding cracks in pipes
- sterilising medical instruments
- killing cancer cells - radiotherapy
- chemical tracers
- dating archaeological finds
how do smoke detectors use radiation?
- alpha as the smoke will stop it reaching the detector
- source with a long half life is chosen to it doesn’t need replacing
how is radiation used to measure the thickness of materials?
- beta as the count is reduced if the material gets too thick
- source with a long half life is chosen to it doesn’t need replacing
how is radiation used to find cracks in pipes?
- beta as this will pass through the crack but not the pipe
- gamma would pass anyway, alpha would not pass through air
how is radiation used to sterilise medical instruments?
gamma radiation which destroys any contaminating bacteria
how is radiation used in radiotherapy?
gamma which kills cancerous cells, but can also damage healthy cells
how do chemical tracers use radiation?
- gamma as this will not be absorbed as much by the body and can be detected outside
- short half life
what can radiation exposure do?
- mutate DNA
- damage cells
- increase risk of cancer
list as many sources of background radiation as you can.
- natural
- air
- cosmic rays
- ground and buildings
- food and drink
- air travel
- artificial
- medical
- nuclear weapons
- nuclear power
describe the process of Nuclear fission
- uranium-235 or plutonium-239 nucleus hit by a neutron
- large nucleus splits into 2 smaller nuclei - barium and krypton
- 2 or 3 more neutrons are released - these fission neutrons are capable of causing another fission event and starting a chain reaction
- some energy is released, and gamma rays
how is nuclear fission controlled in a nuclear reactor?
control rods made of boron (dense and absorbent) are moved down to slow the rate of reaction by absorbing neutrons, or vice versa
describe the process of nuclear fusion
- under huge pressure, nuclei can fuse to make larger nuclei (eg hydrogen nuclei can fuse to make helium)
- lot of energy produced as some mass is converted into energy
During nuclear fusion, does the total mass of the particles decrease or increase?
decrease - some mass converted to energy
The idea of obtaining power from nuclear fusion was investigated using models. The models were tested before starting to build the first commercial nuclear fusion power station. Suggest why models were tested.
- to make sure the fusion process is possible
- to develop an understanding of the process / to make adaptations to the process
- to assess the efficiency of the process
- to make predictions
- assess safety risks
- to assess environmental impact
- set-up cost is lower
