atomic structure

What did john dalton discover about the atom

Said all atoms were empty space but made up elements

explain alpha properties

• alpha is the same as a helium NUCLEUS as consists of 2p and 2n

• it has lowest penetrating power so is absorbed by a think sheet of paper/ skin

• and only travels short distance through air

• this is because it has the highest ionising power and has +2 charge

explain beta

• a beta particle is a fast moving electron which is emitted from nucleus

• beta has moderate penetrating power as cannot penetrate through 5mm aluminium

• travels a longer range in air than alpha (1m)

• because it is more ionising than alpha (medium) and has a -1 charge

explain gamma properties

• it is a electromagnetic wave so high energy

• gamma is the most penetrating as is only stopped by serveral cm if lead or thick concrete

• largest range in air

• because gamma is least ionising and has neutral charge

what happens to the atom when a alpha particle is emitted

what happens to the nucleus

• 2p and 2n released

• nucleus: smaller by 2p and 2n and new element

what happens when beta particle emitted from nucleus

• a fast moving electron is released from nucleus

• so a neutron turns into a proton

what happens when gamma is released from nucleus

nothing is released from nucleus but caused nucleus to have less energy

order of stuff in atom

1. atom empty space

2. electrons

3. nucleus

4. shells

5. proton

6. neutron

What did JJ Thompson discover

Atoms have Electrons that have a negative but space of atom is positive which makes overall charge of atom neutral

What was the name of Jj Thompsons model

Plum pudding model

• electrons had negative charge

• Space of atom positive

• Overall charge neutral of atom

What did Rutherford discover

He discovered most of the atom was empty space but had a nucleus in centre which had a positive charge and held most of atoms mass

Explain differences with beta, gamma and alpha radiation

Alpha: high ionising power, weak penetrating power, 2 protons ad neutrons, +2 charge, same as helium atom

Beta: medium ionising and penetrating power, -1 charge, electron

Gamma: weak ionising power, high penetrating power, neutral charge

Explain the alpha scattering experiment

A beam of alpha particles were shot at a thin piece of gold foil

What were the results of alpha scattering experiment

• most particles went straight through : most of atom was empty space

• Some slightly deflected/bounced back : atom had something small and hard in centre which was nucleus

• Few deflected : nucleus had positive charge and so did alpha particle so like charges repel and contained most of atoms mass

What was the change Rutherford made from plum pudding model

Atom had a nucleus with a positive charge

• electrons orbit around nucleus

How many times bigger is a helium atom than alpha particle

More than 10,000 times bigger

What happens when a isotope emits alpha radiation/decay

Mass number decreases by 4 and atomic number decreases by 2

What happens when ana isotope emits beta radiation/decay

Mass number stays same but atomic number increases by 1

Explain differences between

What did bohr discover

Electrons orbit around the nucleus in shells/energy levels

What did Chadwick discover

Neutrons

What is the final model o the atom

• nucleus is made up of positively charged protons and neutrally charged neutrons so is positive charged

• Electrons which are negatively charged orbit around nucleus in shells

• Atom holds same amount of protons and neutrons

What is the nucleus

Dense core of protons and neutrons that is positively charged

What is the radius of an atom

1 × 10 (-10) m

Radius of nucleus

1 × 10 (-14)

Where is most mass of an atom concentrated

In nucleus

What proportion of radius of atom is radius of nucleus

1/10,000

What charge do atoms have and why

• positive charge

• Protons are positive charge

• Neutrons are neutrally charged

Give two ways an atoms electron arrangement ca be changed

1. Absorbing electromagnetic radiation in which they gain energy and move to higher energy level and move further from nucleus

2. Emitting electromagnetic radiation in which they lose energy and move to lower energy level and move closer to nucleus

What charge does overall atom have and why

• no overall charge

• Same number of protons and electrons

• Protons have positive charge and electrons have negative charge so charges cancel out

What is atomic number

Bottom number which is number of protons and electrons

What is mass number

Top number, number of protons and neutrons

What is an isotope of an atom

An atom of an element with the same number of protons but different number of neutrons

How do atoms turn to positive ions

• they lose one or more outer shell electrons

• Electrons are negatively charged so result of atom is positive

What charge And mass does proton have

• mass is 1

• Charge is +1

Charge of neutron and mass

• mass is 1

• Charge is 0

Charge an mass of electron

• charge is -1

• Mass is 0

Why do unstable nuclei give out radiation

To become more stable as stability increases as they release radiation

What is the name of the process which an unstable nuclei gives out radiation to become more stable

Radioactive decay

What is unit of radioactive activity

Becquerel (Bq)

What is count rate

The number of radioactive decays per second of a radioactive source

What could be used to measure count-rate

Geiger muller tube

State three types of nuclear radiation

• alpha

• Beta

• Gamma

What is an alpha particle made up of

• 2 protons and 2 neutrons

• Same as helium nucleus

What happens in alpha radiation

• dont penetrate far into materials, can only travel few cm in air and can be absorbed by sheet of paper

• Strongly ionising

practical to measure if a source emits alpha,beta, gamma

• move detector close to the source and record initial count rate

• move thin paper between source and detector

• alpha radiation won't penetrate through so if count rate of source is lower that means it has emitted

• as paper will absorb alpha radiation

as count rate= number of radioactive decays per sec and alpha emitted caused decay

how to test if a source emits beta

• repeat past but replace paper position with aluminium sheet

• if count rate significantly decreases this means it has emitted beta as beta is absorbed by aluminium sheets

• but if stays the same or increases this shows its gamma as gamma particles will pass through

What is a beta particle

Fast moving electron which is released from nucleus

What happens in beta nuclear radiation

• penetrate moderately far into materials

• Stopped by 5mm aluminium

• Travel few metres in air

• Moderately ionising

What happens when a beta particle is emitted/released from nucleus

Neutron in nucleus turns to proton

What is a gamma particle

Waves of electromagnetic radiation Released by nucleus

Explain gamma nuclear radiation

• penetrate far into materials and long distance through air

• Absorbed by metres of concrete of thick sheets of lead

• Weakly ionising as they pass through rather colliding with atoms

What radiation is most ionising

Alpha

What radiation is least ionising

Gamma

Wha can be used to show radioactive decays

Nuclear equations

What is another name for nuclear radiation

Radioactive decay

What happens when an atoms electron emits an alpha particle/alpha decay occurs

• Atomic number ( protons) reduce by 2

• mass number reduce by 4

What happens when beta decay occurs

• a neutron turns into a proton and fast moving electron released from nucleus

• Atomic number increases by 1 (number of protons)

• Mass number stays same

What happens in gamma decay/ gamma ray released from nucleus

No change

how to know if a source has more stable nuclei

will have longer half life as more stable nucleus is means the less likely it is to decay

Describe nature of radioactive decay

• random

Define half-life of a radioactive isotope

• time it takes for number of unstable nuclei in a substance to halve

What is radioactive contamination

Unwanted radioactive isotopes end up on other materials

Why is contamination a hazard (what happens when u touch radioactive substance)

Contaminating atoms can decay which release radiation which causes you harm

When is contamination dangerous

If it gets into body

How to reduce getting contamination

• use gloves and tongues when handling sources

• Protective suit to avoid inhaling substances/lab coat with gas mask

What is irradiation

The process of exposing a material to nuclear radiation

Why is it important for results of studies on effects of radiation to be published and shared with other scientists

To allow findings to be independently checked (peer review)

How to reduce irradiation

• keep sources in key and lead lined boxes

• Stand behind bars when handling substances

During alpha radiation is contamination or irradiation the most concern inside the body and outside the body differences

Contamination is of alpha particles is most dangerous inside the body

• irradiation (alpha particles outside body) will be less harmful as alpha has a low penetrating power so can be stopped by dead skin cells and won’t be able to penetrate through human skin

• contamination will be more harmful as it can be absorbed by living tissues as alpha radiation is highly ionising so cause greater risk of harm to tissues

When is alpha radiation the most dangerous and what is its ionising power

• dangerous inside body if inhaled or swallowed

• Strongly ionising but stopped by dead skin cells

How dangerous i beta radiation And what is it like if happens in body

• less dangerous than alpha in body as radiation absorbed over wider area and some pass out altogether

• Quite ionising and can penetrate into skin then into body

What is gamma radiation like in body

• least dangerous

• Ionising power is weak

• Can penetrate into body but likely to pass through and not cause harm

Explain how an atoms electron arrangement can change once absorbed EM radiation

• electrons move further away from nucleus

• They move to a higher energy level

Explain how an atoms arrangement changes when it emits electromagnetic radiation

• electrons move closer to nucleus To lower energy level

Are isotopes stable

Only some are stable the others aren’t so have to give out radiation to become stable

for radioactive isotopes of it as done passed more half lifes what does this show

• it is less harmful

• as it is more stable since released more radiation to become stable

• so dosage of new radiation released would be smaller

• eg 100 → 50 → 25 → 12.5 (gets smaller)

what does it tell us if it has passed less half lives

• source is more unstable

• so would be a higher risk as will continue to half releasing higher radiation

What is count rate

The number of radioactive decays per second of radioactive source

Why is a source of beta radiation more hazardous than a source of alpha radiation?

Because beta radiation can penetrate through materials more easily causing harm than alpha

how does chemotherapy/radiotherapy work

• gamma emitters are used so gamma rays penetrate through human skin

• which are directed onto areas of body with infected/cancerous cells

• they will absorb radiation and die to prevent disease spreading through body

disadvantage of radio/chemotherapy

• difficult to direct accurately to only destroy infected cells so healthy cells may be damaged and killed (irradiated) causing ill side effects

what are the harms with ionising radiation

• if it penetrates through human body, radioactive isotopes can decay and release radiation to healthy cells

• which damages cells and can cause them to mutate DNA

• leading to cancer

what are the side effects of high amount of radiation entering body

• tiredness

• sickness ( feel ill )

• hair loss

how may ionising radiation be a benefit to humans

• can be used as radiotherapy to destroy cancer cells

what are the two types of radiotherapy

• external souces which use gamma rays - less harmful as pass straight out body

• internal sources - which use beta radioactive source by placing it near infected/damaged cells

what is a medical tracer

it is a radioactive isotope that is used to track movement around the body (eg blood) and normally use gamma

why for medical tracers is gamma radiation used

• it is lowest ionising power so it less harmful to body cells as can pass straight out body rather releasing radiation

how do medical tracers work

• inject radioactive isopropyl

• which can be used to track movement of isopropyl around body to track radiation they emit

• to check if organs working properly by checking that absorb normal amount by organs

how to minimise harm of medical tracers

• use gamma radiation

• use radioactive isotopes with shortest half life as possible to will emit radiation for a short period and then pass out the body

• use low dose