4-ATOMIC STRUCTURE

Question 1

model number 1- what does democritus and john dalton say

Answer 1

1804= matter was made up of tiny spheres (atoms) that could not be broken up= he reckoned each element was made up of a different type of atom

Question 2

model number 2- JJ thomson

Answer 2

around 100 years later, he discovers particles called electrons that could be removed from atoms- showing that daltons theory was not quite right
thomson suggested atoms were spheres of positive charge which negative electrons stuck in them like fruit in a plum pudding- model

Question 2

model number 2- JJ thomson

Answer 2

around 100 years later, he discovers particles called electrons that could be removed from atoms- showing that daltons theory was not quite right
thomson suggested atoms were spheres of positive charge which negative electrons stuck in them like fruit in a plum pudding- model

Question 3

model numer 3- Rutherford 1909-alpha scattering experiment

Answer 3

scientists in Rutherford’s lab fired beams of alpha particles at thin gold foil =although most particles went straight through sheet, some were deflected more than expected ,many deflected straight back =
-scientists realised that most of the mass of the atom must be concentrated in centre at nucleus = nucleus has positive charge =it repelled positive alpha particles
-most alpha particles passed straight through, most of atom is just empty space

Question 4

model number 4
-niels bohr= nuclear model

Answer 4

nuclear model resulted from alpha scattering experiment
positively charged nucelus surrounded by cloud of negative electrons
bohr said electrons orbiting nucleus do at certain distances called energy levels. =this agreed with experimental data

further evidence changed model to have nucelus made up of a group of particles (protons) which all had same positive charge adding up to overall charge of the nucleus

Question 5

model 5- 1932
James Chadwick

Answer 5

20 years after the idea of the nucleus was accepted, james chadwick proved existence of neutron explaining imbalance between atomic and mass numbers

Question 6

model 6-explain the current model of the atom

Answer 6

-nucleus is tiny but makes up most of the mass of the atom=contains protons(positive +1 charge ), neutrons =charge of 0, giving overall positive charge(radius of nucleus is 10000x smaller than radius of atom)
=rest of atom is empty space, negative elctrons (-1) on shells,gives atom overall size, radius is 1 x 10^-10 m
number of protons=number of electrons= equal but opposite charge

Question 7

explain how energy levels work in the current model of the atom

Answer 7

electrons in energy levels move within/ leave atom. if they gain energy by absorbing EM radiation, they move to a higher energy level further from the nucleus.
if they release EM radiation, move to a lower energy level closer to the nucleus, if one/more electrons leave atom=atom becomes positively charged ion

Question 8

atomic number

Answer 8

set number of protons(so each nucleus has a given positive charge )
number of protons in an atom is its atomic number

Question 9

mass number

Answer 9

it is the mass of the nucleus
number of protons + number of neutrons

Question 10

what are isotopes

Answer 10

-atoms with same number of protons (same atomic number=same charge on nucleus)
-different number of neutrons (different mass number)

Question 11

simple definition of radioactive decay

Answer 11

unstable isotopes tend to decay into other elements and give out radiation as they try to become more stable

Question 12

what do radioactive substances ‘‘spit out’’

Answer 12

one or more types of ionising radiation from their nucleus= alpha, beta, gamma radiation
also releases neutrons when they decay as they rebalance their atomic and mass number

ionising radiation knocks electrons off atoms creating positive ions . ionising power of a radiation source is how easily it can do this

Question 13

explain properties of alpha radiation
⍺

Answer 13

they are helium nuceli

alpha radiation is when an alpha particles ( ⍺) is emitted from nucelus

⍺ particle is 2 neutrons and 2 protons like a helium nucleus

dont penetrate very far into materials, stopped quickly

can only travel a few cm in air and are absorbed by a sheet of paper

because of size,they are strongly ionising

Question 14

explain beta radiation
β

Answer 14

beta particle is fast moving electron released by the nucleus
= virtually have no mass and a charge of -1

moderately ionising

penetrate moderately far into materials before colliding

has a range in air of a few metres

absorbed by a sheet of aluminium(around 5mm)

for every beta particle emitted, a neutron in the nucleus has turned into a proton

Question 15

explain gamma radiation
ɣ

Answer 15

gamma rays are waves of electromagnetic radiation released by the nucleus

penetrates far into materials without being stopped, will travel long distance through air

weakly ionising because they tend to pass through rather than collide with atoms, eventually they hitsomething and do damage

can be absorbed by thick sheets of lead or metres of concrete

Question 16

what can alpha radiation be used for

Answer 16

can be used in smoke detectors= it ionises air particles using a current to flow, if there is smoke in the air , it binds to the ions meaning the current stops and the alarm sounds

Question 17

what are beta emitters used for

Answer 17

used to test the thickness of sheets of metal as particles are not immediately absorbed by the material like alpha radiation would be and do not penerate as far as gamma rays

Question 18

explain how nuclear equations work

Answer 18

total mass and atomic numbers have to balance

shows radioacitve decay by using element symbols

atom before decay => atom after decay + radiation emitted

Question 19

how does alpha decay work

Answer 19

it always emits an alpha particle(helium nucleus)

use this to calculate the remaining mass and atomic numbers

eg.
238 = 234 + 4
U => Th + He
92 = 90 + 2

new element formed bc atomic number changes

Question 20

explain beta decay

Answer 20

when beta decay occurs, neutron in nucleus turns into a proton and releases fast moving electron(beta particle)

number of protons in nucleus has increased by 1
=increasing + charge of nucleus (atomic number)

nucleus has lost a neutron, gained proton, mass doesnt change

e.g.
14 14 0
C => N + e
6 7 -1

new element is formed bc atomic number changes

Question 21

why dont gamma rays change charge or mass of nucleus

Answer 21

gamma rays are a way of getting rid of excess energy from a nucleus

there is no change to the atomic mass or atomic number of the atom

Question 22

what can radiation be measured with

Answer 22

geiger muller tube and counter

this records the count rate (the number of radiation counts reaching it per second)

Question 23

what does it mean when someone says radioactive decay is random

Answer 23

you cannot predict which nucleus in a sample will decay next or when any one of them will decay

Question 24

what is half life and what can this be used for

Answer 24

the time it takes for the amount of radiation emitted by a source to halve= half life
its used to make predictions about radioactive sources even though decays are random
it can be used to find the rate at which a source decays= this is the activity which is measured in bequerels
(1 Bq= 1 decay per second)

Question 25

what is activity

Answer 25

half life is used to find the rate at which a source decays = the activity
which is measured in bequerels
1 Bq = 1 decay per second

Question 26

how does the radioactivity of a source decrease over time

what is the problem that occurs with this

Answer 26

each time a radioactive nucelus decays to become a stable nucelus the activity as a whole will decrease (older sources emit less radiation)

for some isotopes it takes a few hours before nearly all unstable nuclei have decayed, whilst others last for a million years

the problem with trying to measure this is that the activity never reaches 0 which is why half life is used to measure how quick the activity drops off

Question 27

what is half life

Answer 27

the time taken for the number of radioactive nuclei in an isotope to halve

it is also
the time taken for the activity(count rate) to halve

Question 28

what is meant by a short half life

Answer 28

the activity falls quickly
because the nuclei are very unstable and rapidly decay

sources with a short half life are dangerous bc of the high amount of radiation they emit at the start but they quickly become safe

Question 29

what is meant by a long half life

Answer 29

activity falls more slowly because most of the nuclei dont decay for a long time- the source just sits there releasing small amounts of radiation for a long time
, this can be dangerous because nearby area are exposed to radiation for (millions of) years

Question 30

practice q
how would you calculate the final activity as a percentage of the initial activity (640 Bq)after 2 half lives

Answer 30

e.g. 640 Bq
1 half life= 640/2=320
2 half lives=320/2=160

160/640= 0.25 x 100= 25 %

Question 31

how can you measure half life using a graph

Answer 31

if you plot a graph of activity against time (taking into account background radiation) line with curve descending downwards

half life is found from graph by finding time interval on the bottom axis corresponding to a halving of the activity on vertical axis

Question 31

how can you measure half life using a graph

Answer 31

if you plot a graph of activity against time (taking into account background radiation) line with curve descending downwards

half life is found from graph by finding time interval on the bottom axis corresponding to a halving of the activity on vertical axis

Question 31

how can you measure half life using a graph

Answer 31

if you plot a graph of activity against time (taking into account background radiation) line with curve descending downwards

half life is found from graph by finding time interval on the bottom axis corresponding to a halving of the activity on vertical axis

Question 31

how can you measure half life using a graph

Answer 31

if you plot a graph of activity against time (taking into account background radiation) line with curve descending downwards

half life is found from graph by finding time interval on the bottom axis corresponding to a halving of the activity on vertical axis

Question 32

explain what background radiation is

Answer 32

low level radiation that is around us at all times

you should always measure and substract background radiation from results to avoid systematic errors

Question 33

where does background radiation come from

Answer 33

1- radioactivity of naturally occuring unstable isotopes around us- in air, food, building materials, rocks under our feet
2- radiation from space= cosmic rays, mostly from Sun= but earths atmosphere protects us from much of this radiation
3- radiation due to human activitye.g. fallout from nuclear explosions/waste= but this represents a tiny proportion of the total background radiation

Question 34

what is radiation dose

Answer 34

the risk of harm to body tissues due to exposure to radiation
measured in sieverts(Sv)
the dose from background radiation is small so milliseverts are used
(1Sv=1000mSv)

radiation dose varies depending on where you live/ if you have a job the involves radiation

Question 35

what is irradiation

Answer 35

objects near a radioactive source is irradiated by it. (exposed to a radioactive source) we’re always being irradiated by background radiation sources

irradiating something does not make it radioactive

=keeping something in lead lined boxes(standing behind barrier/ being in a different room and using remote controlled arms help reduce effects or irradiation)

Question 36

what is contamination

Answer 36

if unwanted radioactive atoms get onto/ into an object= it is contaminated
e.g. if you touch a radioactive source without wearing gloves= hands would be contaminated

contaminating atoms might then decay releasing radiation that could cause harm

contamination is dangerous because radioactive particles could get inside your body

gloves and tongs should be used when handling sources to avoid particles getting stuck on skin/under nails= industrial workers wear protective suits to stop them breathing in particle

Question 37

ways to avoid contamination

Answer 37

gloves and tongs should be used when handling sources to avoid particles getting stuck on skin/under nails= industrial workers wear protective suits to stop them breathing in particle

Question 38

explain how the seriousness of irradiation and contamination depends on the source

Answer 38

1- outside the body= beta & gamma sources are most dangerous, beta & gamma penetrate the body to get to delicate objects
(alpha is less dangeous bc it cant penetrate the skin, easily blocked by a small air gap) high levels of irradiation from all sources are dangerous(esp ones emitting beta and gamma)

2- inside body= alpha is most dangerous bc all damage is done in very localised area, contamination is major concern when working w alpha sources.
beta =less damaging inside body=radiation absorbed over wider area & some passes out of body altogether.
gamma sources least dangerous inside body= most passes straight out(has lowest ionising power)

Question 39

why is it important for data to be published

Answer 39

so it can be peer reviewed, can be quickly accepted leading to more improvements in use of radioactive sources

Question 40

risks of using radiation

Answer 40

• can enter living cells and ionise atoms and molecules within them leading to tissue damage
• lower doses tned to cause minor damage without killing the cells=gives rise to mutant cells which divide uncontrollably=cancer
  -higher doses kill cells completely, causes radiation sickess(vomiting,tiredness,hair loss)if a lot of cells all get blatted at once

Question 41

how are gamma sources used in medical tracers

Answer 41

certain radioactive isotopes can be injected into people (or swallowed) and progress in body can be followed with external detector, computer converts reading to a display showing where the strongest reading is coming from
e.g. iodine 123 absorbed by thyroid gland like iodine 127=gives out radiation which can be detected to indicate whether thyroid gland is taking in iodine as it should
- isotopes taken into body like this is usually GAMMA(never alpha) so radiation passes out of body without causing much ionisation=should have short half life , radioactivity inside patient quickly disappears

Question 42

how is cancer treated with radiation

Answer 42

radiotherapy= high doses of ionising radiation kills all living cellls= used to treat cancers
gamma rays directed carefully , at right dosage to kill cancer cells without damaging too many normal cells
radio emitting implants (beta emitters) can be out next to/inside tumours
(bit of damage is inevitable done to normal cells, makes patient feel very ill)

Question 43

alternative risks and benefits of using radioactive materials

Answer 43

tracers can be used to diagnose life threatening conditions while risk of cnacer from one use of a tracer is very small

prolonged exposure to radiation poses future risks causing side effects, those with cancer may choose to have radiotherapy as it may get rid of cancer entirely(benefits outweigh risks)

Question 44

what is perceived risk

Answer 44

how risky a person thinks something is , not the same as actual risk of a procedure, can vary from person to person

Question 45

what is nuclear fission

Answer 45

type of nuclear reaction used to release energy from large and unstable atoms (uranium/plutonium) by splitting them into smaller atoms

spontaneous fission rarely happens, nucleus has to absorb neutron before split
when atom splits, it forms 2 new lighter elements= roughly same size, w energy in kinetic energy stores

2/3 neutrons released when atom splits , if any neutrons are moving slow enough to be absorbed by another nucleus = causes more fission to occur=chain reaction

energy not transferred to kinetic energy store is carried away by gamma rays

energy carried away by gamma rays and in kinetic store of remaining free neutrons & other decay products can be used to heat water making steam to turn turbines and generators

Question 46

explain how chain reactions

Answer 46

2/3 neutrons released when atom splits , if any neutrons are moving slow enough to be absorbed by another nucleus = causes more fission to occur=chain reaction

Question 47

during nuclear fission,what can energy carried by gamma rays and in kinetic stores be used for ?

Answer 47

used to heat water to make steam to turn turbines and generators

Question 48

how can the amount of energy produced by fission in a nuclear reactor be controlled

Answer 48

by changing how quickly the chain reaction can occur
done by using control rods which are lowered and raised inside a nuclear reactor to absorb neutrons
slows down chain reaction and controls amount of energy released

Question 49

how do nuclear weapons work

Answer 49

uncontrolled chain reactions lead to lots of energy being released as an explosion

Question 50

explain nuclear fusion

Answer 50

opposite of nuclear fission

2 light nuclei collide at a high sped and join (fuse) to create larger, heavier nucleus e.g. hydrogen nuclei can fuse to produce a helium nucleus

heavier nucleus produced by fusion=doesnt have as much mass s the 2 separate nuclei did
mass of lighter nuclei is converted to energy which is released as radiation

fusion releases a lot of energy(more than fission does for a given mass of fuel)

scientists have not found a way of using fusion to generate energy to use=temperatures and pressure needed for fusion so high that fusin reactors are hard and expensive to build

Question 51

why have scientists not found a way of using to fusion to generate energy to use

Answer 51

scientists have not found a way of using fusion to generate energy to use=temperatures and pressure needed for fusion so high that fusin reactors are hard and expensive to build