P4 - Atomic Structure

Atomic Structure:

Early Ideas

matter made up of undetectable pieces of that same matter

Atomic Structure:

Plum Pudding Model

Atoms look like a plum pudding

positive ‘dough’

negative electrons within

Atomic Structure:

Rutherford

Fired alpha (+) particles at thin piece of gold

most passed straight through = atoms mostly empty space

small number deflected at large angles = + charge inside atoms (like charges repel!)

very small number coming back = + charge is concentrated in small volume

Atomic Structure:

Neil Bohr

Electrons in shells/energy levels

coloured flames shows energy release from electrons moving down energy levels

Atomic Structure:

James Chadwick

Proved existence of neutrons

similar experiment to Rutherford

Used sheet of Be and paraffin block instead of gold

Mass Number

Sum of number of protons + neutrons

Atomic Number

Number of protons = number of electrons

Number of Neutrons =

mass number - atomic number

Isotopes

Atoms of the same element with the same numbers of protons and electrons but

different number of neutrons

Reactivity of Isotopes

Same between different isotopes because same electron structure

Ions

atoms that have gained/lost electrons

forming charges

Stable Nuclei

neutrons and protons in proportion

Unstable Nuclei

nucleus with too many/few neutrons

will decay by emitting radiation

Alpha Radiative decay

nucleus has too few neutrons

emits 2 protons & 2 neutrons

Beta Radioactive Decay

nucleus has too many neutrons

emits an electron

Gamma Radioactive Decay

after alpha or beta decay

nucleus too hot still

emits gamma rays as it cools

mass and atomic numbers remain the same

Neutron Emission (Radioactive Decay)

neutron emitted

natural or artifical process

mass number -1

atomic number the same

Properties of Nuclear Radiations:

Ionising Power

Ability of radiation to ionise (provide a charge) to an atom

Properties of Nuclear Radiations:

Penetrating Power

how far into a material radiation will travel

Half-Life

time required for half an unstable nuclei to decayC

Count Rate

number of decays recorded each second

Irradiation

Exposure of an object to a radiation source

Advantages of Irradiation

Sterilises without high temperatures

kills bacteria on things that would melt

Disadvantages of Irradiation

may not kill all bacteria

can harm living cells too

Contamination

an object has radioactive material introduced to it

Advantages of Contamination

radioactive isotopes used as medical and industrial tracers

isotopes with small half-lives means limited exposure

imaging processes can replace some invasive surgical procedures

Disadvantages of Contamination

radioactive isotopes may not follow a path exactly

small amounts may be left behind

potential damage to healthy cells

Effects of Radiation on the Human Body

eyes - cataracts

Thyroid - Cancer

Lungs - damages DNA

Stomach - remains and continues irradiation

reproductive organs - sterility or mutations

skin - burns and cancer

bone marrow - leukaemia and other blood disease

Managing Risks of Radiation

keeping sources shielded, e.g., in lead boxes

protective clothing

avoid skin contact

face masks

limited exposure times

tongs - safe distance away

monitoring equipment, e.g., detector badges

Nuclear Fission

splitting of large nuclei into small

1. neutron absorbed into nucleus

2. becomes unstable

3. split into 2 daughter nucleus

4. additional neutrons released

5. Repeat

How can Nuclear Fission produce electricity?

energy release during

energy heats power into steam

steam turns turbines

generators produce electricity

Fission Reactors:

Nuclear Fuel

rods held in so neutrons released will fly out and cause fission

Fission Reactors:

Graphite Core

slows neutrons down to increased adsorption to nearby rod

Fission Reactors:

Control Rods

Raised and lowered to stop neutrons changing speed of reaction

Fission Reactors:

Coolant

Drives turbines in power stations

Fission Reactors:

Concrete Shield

prevents release of radioactive materials

Nuclear Fusion

forming heavy nucleus from 2 small light nuclei

in stars under high temperature and pressure

forms He nuclei

release of energy as mass is lost

process powers sun and other stars