Atomic Structure

approximate radius of an atom

1 × 10^10

radius of a nucleus

less than 1/10000 of the atom

current model of the atom

• nucleus at the centre

• proton, neutron and electrons

• mainly empty space

• electrons orbit in shells

What were atoms through to be before the discovery of the electron

tiny spheres that could not be divided

What did the discovery of the electron lead to?

The plum pudding model

Plum pudding model

atoms are a ball of positive charge with negative electrons embedded in it

What did Niels Bohr suggest about electrons

They orbit the nucleus at specific distances

Who discovered the neutron

James Chadwick

Rutherford’s Alpha scatterring Experiment

• fired alpha particles at a thing gold foil

• most particles travelled straight through the foil

• some were slightly deflected and very few were deflected straight back

Conclusion of the experiment

Most of the atom is empty space, with a small, dense, positively charged nucleus that causes the deflection of some alpha particles.

isotope

same number of protons

different number of neutrons

• charge doesnt change

• mass changes

ion

different number of protons

same number of neutrons

• charge does change

• mass doesnt change

alpha radiation α or ⁴₂He

• helium nucleus (2 protons 2 neutrons)

• an alpha particle is emitted from the nucleus

• strongly ionising

• weakly penetrating

• doesnt travel far in air (few cm)

• stopped by paper

• used in smoke detectors

beta radiation β or ⁰₋₁e

• fast moving electron released by the nucleus

• moderately ionising

• moderately penetrating

• travels further in air (few metres)

• stopped by aluminium

• used in material thickness testing

gamma radiation γ

• an electromagnetic wave released from the nucleus

• weakly ionising

• highly penetrating

• travels far in air

• stopped by lead

• used in sterilising medical equpment

what is half life

The time taken for half of the radioactive nuclei in a sample to decay.

radiation is a random process.

what is radiation measured with

a Geiger-Muller counter

What is activity?

the rate at which the source decays

it is measured in becquerels

What do radioactive sources give out as they decay?

radiation

risks of radiation

• irradiation

• contamination

irradiation

• exposure to radiation

• usually beta or gamma as they can penetrate the skin

• can be reduced by keeping sources in a lead lined box

contamination

• radioactive particles that get onto objects

• usually alpha as they damage in a localised area

• can be prevented by using the correct PPE such as gloves or special suits

atomic number

the number of protons in an atoms nucleus

mass number

total number of protons and neutrons