Physics Topic 4 Atomic Structure

1-6 people developing the model of atom

Democritus-matter made up of tiny particles

John Dalton 1804-Atoms described as solid spheres. each element had a different type .

JJ Thompson1897- discovered electrons, he thought they could be removed. Plum pudding model the atom was a ball of positive charge with electrons scattered within.

Ernest Rutherford1909- Alpha scattering experiment, he shot a beam of alpha particles at thin gold foil expecting most of them to pass through but more than expected deflected and a few deflected back the way they had come so scientists realised most of the mass in an atom was concentrated at the centre in a tiny nucleus

Niels Bohr1911- noticed light emitted when atoms are heated only had a specific amount of energy so suggested electrons orbit the nucleus at distances called energy levels

Chadwick 1940- discovered neutrons(no charge) which explained the imbalance between the atomic and mass number.

atom size= and atom nucleus size=

1×10^-10 m 1/10000(nucleus)

Unstable isotopes tend to …

Known as…

decay into other elements and give out radiation as they try to become more stable radioactive decay

Ionising radiation is ..

ionising power -

radiation that knocks of electrons of their atoms creating positive ions.

how easily it can do this is ionising power

Alpha radiation

it can be used for…

when an alpha particle(2neutrons and 2 protons like helium nucleus) is emitted from the nucleus.

doesn’t penetrate far stopped by a sheet of paper

can only travel a few cm in air

strongly ionising because of it’s size smoke detectors

Beta particle …

for every…

fast moving electron released by the nucleus moderately ionising moderately far penetration into materials range in air is a few m absorbed by a sheet of aluminum around 5mm thick .

every beta particle emitted a neutron in the nucleus turns into a proton

gamma radiation…

often after… (nucleus) oak national pptx

waves of electromagnetic radiation released by the nucleus, penetrates far into materials travels a long distance through air several km. weak ionising because they pass through and don’t collide with atoms absorbed by thick sheets of lead. no change to mass or atomic number way of getting rid of excess energy.

alpha and beta particles emitted the nucleus is in an excited state so it releases gamma radiation to become unexcited lose energy

nuclear equations the mass and atomic numbers must be

beta decay (equations)

equal on both sides a neutron in the nucleus turns into a proton and releases a fast moving electron(beta particle)

alpha beta gamma radiation inside outside body…

these radiations can cause…

Alpha more dangerous inside-highly ionising can cause lots of damage (cells) less dangerous outside it can’t penetrate the skin. Beta is less dangerous inside the body- some of the radiation is able to escape outside more dangerous as it can penetrate the skin. Gamma is least dangerous inside the body as most will pass out and is least ionising outside can penetrate skin and damage internal organs.

cancer

Radioactivity can be…

measured using a Geiger muller tube and counter which records the count rate

count rate-

number of radioactive decays detected

half life

the half life is used to …

time taken for the amount of radiation emitted from a source or number of nuclei to halve

make predictions and find the rate of which a source decays

Activity-

measured in Bq-1 decay per second rate at which a source decays

what does a short on long half life mean?

short half life means activity falls quickly because nuclei are very unstable and rapidly decay- dangerous at start(emits a lot of radiation) long half life means activity falls more slowly, most nuclei dont decay for a long time releasing small amounts a radiation at an area for a long time (millions) of years

Short - activity decreases quickly

risk of harm decreases quickly

Background radiation

it comes form

make sure you always

low level radiation that is all around us. radiation from space cosmic rays naturally occurring unstable isotopes human activity fallout form nuclear explosion

subtract from your result

Irradiation

Safety

Precautions

when objects are near a radioactive source. Keep in a lead lined box stay behind barriers and use remote controlled arms

Contamination

safety

precaution

when unwanted radioactive atoms that could decay releasing radiation causing harm get onto an object - particles can get inside body.

Wear protective clothing, gloves, tongs

Risks with radiation

ionise atoms and molecules within them. lower does may do minor damage but can give rise to mutant cells growing uncontrollably(cancer) high does can kill the cells but cause radiation sickness

Gamma isotopes are used as … because..

medical tracers because they have a short half life so their radioactivity will disappear quickly. tracer are injected or swallowed an a computer converts the reading to a display where the strongest reading is coming from

Nuclear fission -

Usually the nucleus has to …

splitting of a large radioactive nuclei into smaller ones to release energy from large and unstable atoms . Usually the nucleus has to absorb a neutron before it splits. when the atoms splits it forms two lighter elements-two or three neutrons also released when these split . if these neutrons are slow enough to be absorbed by another nucleus this causes a chain reaction(more fission occurs)

GAMMA RAYS EMMITED

energy from nuclear fission

how is it contorlled?

used to heat up water making steam turning turbines. this energy can be controlled using control rods which control how quickly chain reactions occur by absorbing neutrons(slowing the reaction)

Nuclear fusion

joining of light radioactive nuclei join to make a heavier nucleus. -

nucleus not as heavy as the other two nuclei because some of the mass is converted to energy and released

Nuclear Fusion (how much energy)

problems

releases a lot of energy . tempurautres and pressured needed for fusion are so high fusion reactors are expensive to build and really hard to.