Science - Physics - Atomic Structure - P4 Flashcards
what did Democtritus believe about matter in the 5th century BC?
all matter was made up of identical lumps called atoms
what did John Dalton discover in 1804 ?
that each element was made up of a different type of atom
what did JJ Thompson discover ?
electrons could be removed from atoms
what model did JJ Thompson create ?
plum pudding model
what is the plum pudding model ?
atoms where spheres of positive charge with tiny electrons scattered in them
what experiment did Rutherford carry out ?
the alpha particle scattering experiment
what was the alpha particle scattering experiment ?
where scientists fired a beam of alpha particles at thin gold foil
a circular detector screen surrounds the gold foil and the alpha source and is used to detect alpha particles deflected by any angle
what does a circular detector screen do ?
detect alpha particles deflected by an angle
what did Rutherford expect during the alpha particle scattering experiment ?
the positively charged alpha particles to go straight through or be slightly deflected by the electrons if the plum pudding model was true
when did the alpha particle scattering experiment take place ?
1909
what happened in the alpha particle scattering experiment ?
- most alpha particles went straight through the foil but some were deflected more than they had expected and the odd particle deflected straight back at them
what did the results of the alpha particle scattering experiment show ?
atoms must have small positively charged nuclei in the centre
why did the alpha particle scattering experiment show that atoms must have small positively charged nuclei in the centre ?
- most of the atom was empty space as most of alpha particles passed straight through the foil
- nucleus must have a large positive charge as some positively charged alpha particles were repelled and deflected by a big angle
- nucleus must be small as very few alpha particles were deflected back
what structure of the atom did Rutherford create ?
nuclear model
how did Bohr adapt the nuclear model ?
by saying electrons orbiting the nucleus can only do so at certain distances called energy levels
what did Chadwick prove ?
the existence of neutrons
what 3 particles did the nuclear model produce ?
electrons
protons
neutrons
what are electrons ?
negatively charged particles
what are protons ?
positively charged particles
what are neutrons ?
neutral particles
what part of the atom makes up most of its mass ?
nucleus
where is the nucleus ?
in the center of the atom
what does the nucleus contain ?
protons and neutrons
what do electrons do around the atom ?
orbit the outside of the nucleus
what do electrons give the atom ?
its overall size
what is the radius of the atom ?
1 x 10-10 n
what is the relative mass of the proton and neutron ?
1
what is the mass of an electron ?
1/2000
what is the charge of a proton ?
+1
what is the charge of an electron ?
-1
what is the charge of a neutron ?
0
what charge is an atom ?
0
why is the charge on an atom 0 ?
the charge on the electron is the same as the proton
what does the number of protons equal to ?
the number of electrons
how do electrons move further away from the nucleus ?
by gaining energy
absorbing EM radiation
moving to a higher energy level
what happens when electrons release EM radiation ?
they move to a lower energy level that is closer to the nucleus
what is the atomic number ?
the number of protons in the nucleus of an atom
what is the mass number ?
protons + neutrons in the nucleus of an atom
what are ions ?
charged particles
how are ions formed ?
by losing/gaining electrons
what is ionisation ?
the process of an atom having electrons added or removed
what is an isotope ?
different forms of the same element, atoms have the same number of protons but a different number of neutrons
isotopes have the same atomic number but a different …
nass number
what are unstable isotopes ?
radioactive isotopes
what do radioactive isotopes do ?
they decay into other elements and give out radiation
what is radioactive decay ?
unstable isotopes decay into other elements and give out radiation as they try to become more stable
what does radioactive decay being random mean ?
you have lots of unstable nuclei and don’t know when any one of them is going to decay, and you can’t do anything to make a decay happen
what is radioactive decay unaffected by ?
physical conditions
chemical bonding
what do radioactive substances emit ?
ionizing radiation
what is ionising radiation ?
radiation that knocks electrons of its atoms, creating positive ions
what does the ionising power of a radiation source tell you ?
how easily it is to knock electrons off atoms
what do radioactive substances do ?
spit out one or more types of ionising radiation from their nucleus as they decay and may release neutrons to rebalance their atomic and mass numbers
what are the 3 types of radiation ?
alpha
beta
gamma
what is alpha radiation ?
when an alpha particle is emitted from the nucleus
what is an alpha particle ?
2 neutrons and 2 protons
what happens when an atom decays by emitting an alpha particle ?
2 protons and 2 neutrons are lost from the nucleus
as protons have a relative charge of +1, what does alpha emission decrease the charge of the nucleus by ?
2
what does the mass number decrease by during alpha decay ?
4
give properties of alpha particles ?
big
heavy
slow moving
don’t penetrate far into materials
strongly ionising
what does strongly ionising mean ?
they bash into lots of atoms and knock electrons off them before they slow down so makes lots of ions
what is a beta particle ?
a fast moving electron released by a nucleus
what is the mass of a beta particle ?
basically 0
what is the charge of a beta particle ?
-1
what happens when a nucleus decays by beta decay ?
a neutron turns into a proton in the nucleus, releasing a beta particle
what does beta decay do to the charge of the nucleus ?
increase the charge on the nucleus by 1
what does beta decay do to the mass number ?
nothing
what are the properties of beta particles ?
fast
small
moderately ionising
moderately penetrating g
what can alpha particles be absorbed by ?
a sheet of paper
what can beta particles be absorbed by ?
a sheet of aluminium
what are gamma rays ?
very short wavelength electromagnetic waves released by the nucleus
what are the mass and charge of gamma rays ?
they have no mass/charge
what are the properties of gamma rays ?
- penetrate far into materials
- weakly ionising
why are gamma rays weakly ionising ?
they tend to pass straight through rather than collide with atoms, eventually they hit something and do damage
what can gamma rays be absorbed by ?
metre of concrete
what are alpha and beta decays written as ?
nuclear equations
what are nuclear equations ?
reactions that show what atoms you start with, what radiation is emitted and what atoms are left with
what has to be balanced in nuclear equations ?
mass and atomic numbers
what can happen after alpha or beta decay ?
gamma emission to get rid of excess energy
what element is alpha particles ?
helium nuclei
what is a beta particle shown as ?
0
e
-1
what are beta particles ?
electrons
what can radiation be measured with ?
Geiger Muller tubes
what do Geiger Muller tubes do ?
record the number of radiation counts reaching it per second
what is half life ?
the time it takes for the number of nuclei of a radioactive isotope in a sample to halve
what can half life be used to do ?
find the rate at which the source decays - its activity
what is activity measured in ?
becquerals (Bq)
what happens to the radioactivity of a sample over time ?
it decreases
what happens when a radioactive nucleus decays to become a stable nucleus ?
the activity as a whole will decrease = older sources emit less radiation
what is the issue with trying to measure radioactive decay ?
the activity never reaches 0
what does a short half-life mean ?
the activity falls quickly because the nuclei are very unstable and rapidly decay
why are sources with a short half life dangerous ?
they emit high amounts of radiation at the start, but they quickly become safe
what does a long half life mean ?
the activity falls more slowly because most of the nuclei doesn’t decay for a long time
how do things with a long half life release radiation ?
in small amounts, over a long period
why can things with a long half life be dangerous ?
nearby areas are exposed to radiation for years
how do you calculate half life ?
by dividing by 2 until you get to the desired number
how can you use graphs to work out the half life of a radioactive isotope ?
plot the graph of radioactivity against time
how can you find half life on a graph ?
find the time interval on the bottom axis corresponding to a halving activity on the vertical axis
what is irradiation ?
when objects are exposed to radiation
what can you do to reduce risks of irradiation ?
keep sources in lead lined boxes
stand behind barriers
be in a different room and use remote controlled arms to handle sources
what is contamination ?
when unwanted radioactive atoms get onto or into a material
give an example of contamination ?
touching a radioactive source without gloves
how is touching a radioactive source harmful ?
contaminating atoms may then decay, releasing radiation which can harm you
why is contamination harmful ?
radioactive particles could get inside your body
what kind of radiation causes the most harm outside of the body ?
gamma
beta
why is gamma and beta the most harmful radiation outside the body ?
it can penetrate the body and get into delicate organs
why is alpha radiation less dangerous outside of the body ?
it cannot penetrate the skin and is easily blocked by a small air gap
what is the most dangerous type of radiation inside the body ?
alpha
why are beta and gamma sources less harmful inside the body ?
they mostly pass straight out of the body without doing much damage
why is alpha radiation more harmful inside the body ?
they do lots of damage in a localised area
is contamination or irradiation more concerning when working with alpha sources ?
contamination
what is radiation dose ?
a measure of risk of harm to your body due to exposure to radiation
what does radiation dose depend on ?
the type and amount of radiation you are exposed to
the higher the radiation dose the more you have the risk of developing what ?
more risks you have to developing cancer
what is radiation dose measured in ?
sieverts (Sv)
what is the radiation dose due to background radiation ?
small
what is background radiation ?
low level radiation that is present at all times
what does background radiation come from ?
- radioactivity of naturally occurring unstable isotopes
- radiation from space
- radiation due to man made sources
give an example of radioactivity of naturally occurring unstable isotopes ?
air, food, building materials, rocks
what is radiation from space known as ?
cosmic rays
where do cosmic rays come from ?
the sun
give an example of radiation from man made sources ?
nuclear weapons tests
nuclear accidents, e.g Chernobyl
dumped nuclear waste
how does your location affect the amount of radiation you are exposed to ?
- underground rocks cause higher levels of radiation at the surface which can release radioactive radon gas and gets trapped inside peoples houses
people who live at high altitudes are exposed to more background radiation in the form of cosmic rays
what can a radon detector do ?
tell you if your house has a dangerous level of radon
what does a radon outlet piper do ?
keep the level of radon gas down
how does occupation affect the amount of radiation you are exposed to ?
- nuclear industry workers and uranium miners are exposed to 10 times the normal radiation
- radiographers use ionising radiation
- underground miner have rocks around them with radiation
what can nuclear industry workers and uranium miners do to reduce the amount of radiation they are exposed to ?
wear protective clothing and face masks to stop them from touching or inhaling radioactive material
monitor their radiation dose using radiation badges and having regular check ups
how is ionising radiation harmful to living cells ?
they collide with molecules which causes ionisation which damages or destroys the molecules
what do lower doses of ionising radiation do to the cells ?
causes minor damage
this can give rise to mutant cells which divide uncontrollably
the cells keep dividing making more cells, forming a tumour = cancer
what do higher doses of ionising radiation do to the body ?
kill cells completely, causing radiation sickness
what does the extent of the harmful effects of radiation depends on ?
- how much exposure you have to the radiation
- the energy and penetration of the radiation since some types are more hazardous than others
what are medical tracers ?
radioactive isotopes which are injected or swallowed and their progress around the body can be followed using an external detector
how do medical tracers work ?
a computer converts the readings from the external detector to a display showing where the strongest readings are coming from
what do medical tracers help with ?
doctors investigate whether the patients internal organs are functioning as they should be
what type of emitters can enter the body ?
ONLY
beta
gamma
how long should the radioactivity source inside a patient last for ?
a few hours so it quickly disappears
what is radiotherapy ?
a treatment of cancer using ionising radiation e.g gamma rays
what can radiotherapy be used for ?
treating cancer
how does radiotherapy work ?
high doses of radiation kills all living cells including cancer cells
why does radiation in radiotherapy have to be directed carefully ?
so it can kill the cancer cells without damaging to many normal cells
what do radioactive implants do ?
they are put next to tumours
what re the disadvantages of radiotherapy ?
- they damage normal cells making the patient feel ill
what are the advantages of radiotherapy ?
it can get rid of cancer completely
what is nuclear fission ?
a nuclear reaction used to release energy from large and unstable atoms by splitting them into smaller atoms
how does nuclear fission happen ?
the nucleus has to absorb a neutron before it will split
when the atom splits it forms 2 new lighter elements that are roughly the same size
how can more nuclear fission occur during nuclear fission- a chain reaction begin ?
if neutrons released in the original nuclear fission are moving slowly enough to be absorbed by another nucleus causing more fission to occur = chain reaction
in nuclear fission how is the energy not transferred to kinetic energy stores of the product carried away ?
by gamma rays
what can the energy carried away by the gamma rays, and in the kinetic energy stores of the remaining free neutrons and decay products be used for ?
to heat water
to make steam to turn turbines and generators
what is the amount of energy released by nuclear fission controlled by ?
how quickly the chain reaction can occur
how is the amount of energy released by fission controlled ?
by using control rods which are lowered and raised inside the nuclear reactors to absorb neutrons, slow down the chain reaction and control the amount of energy released
what does uncontrolled chain reactions in nuclear fission lead to ?
lots of energy being released as a nuclear explosion = how atomic bombs work
what is nuclear fusion ?
2 light nuclei collide at high speed and fuse to create larger, heavier nucleus
give an example of nuclear fusion ?
hydrogen nuclei fuses to produce a helium nucleus
why doesn’t the heavier nucleus created in nuclear fusion not have the same mass as the 2 separate light nuclei ?
some of the mass is converted into energy and released
