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P4 - Atomic Structure (Isotopes and Nuclear Radiation (Isotopes are…
P4 - Atomic Structure
Isotopes and Nuclear Radiation
Isotopes are Different Forms of the Same Element
They all have a set number of protons - atomic number
Mass number is number of protons and neutrons
Isotopes have the same protons but different neutrons
All elements have isotopes
Unstable isotopes decay into other elements
Radioactive substances give off alpha, beta or gamma radiation
They can release neutrons
Ionising radiation knocks electrons off
Alpha Particles are Helium Nuclei
Consists of two neutrons and two protons
Don't penetrate very far
Strongly ionising
Beta Particles are High-Speed Electrons
No mass and a charge of -1
Moderately ionising
For every beta particle emitted, a neutron turns into a proton
Gamma Rays are EM Waves with a Short Wavelength
Gamma rays are electromagnetic radiation
They penetrate far into materials
They are weakly ionising
Absorbed by thick lead
Nuclear Equations
Mass and Atomic Numbers Have to Balance
Nuclear equations show radioactive decay using element symbols
atom before decay -> atom after decay + radiation emitted
Total mass and atomic numbers must be equal
Alpha Decay Decreases the Charge and Mass of the Nucleus
Made of two protons and two neutrons
Charge of nucleus decreases
Can be written as helium nucleus
Beta Decay Increases the Charge of the Nucleus
A neutron turns into a proton and releases an electron
Nucleus charge has increased by 1
Mass doesn't change
Gamma Rays Don't Change the Charge or Mass of the Nucleus
Ways to get rid of excess energy
No change in atomic or mass number
Irradiation and Contamination
There are Risks to Using Radiation
Ionising radiation can enter living cells and lead to cancer
Exposure to Radiation is called Irradiation
Objects near a radioactive source are irradiated by it
Irradiating something doesn't make it radioactive
Keeping sources in lead boxes reduce risk of irradiation
The source could be in a different room
Contamination is Radioactive Particles Getting onto Objects
If unwanted radioactive atoms get onto something, it's contaminated
These atoms may then decay
Contamination is dangerous if it gets inside your body
Gloves and tongs should be used if handling sources
Some industrial workers wear suits
The Seriousness of Irradiation and Contamination Depends on the Source
Beta and gamma are most harmful outside
Beta and gamma can penetrate the body
Alpha can't penetrate skin
Inside, alpha is most dangerous
High levels of irradiation from all sources is dangerous
Beta sources are less damaging inside the body
Developing the Model of the Atom
Rutherford Replaced the Plum Pudding Model with the Nuclear Model
John Dalton thinks each element is made of a different type of atom
J J Thomson discovered electrons and led to plum pudding model
Rutherford's alpha scattering experiment - plum pudding model couldn't explain it
Most of the mass must be concentrated in nucleus - conclusions from experiment
Most of the atom has to be empty space - nuclear model
...Which Developed into the Current Model of the Atom
Nuclear model was a positive nucleus with a cloud of electrons
Bohr came up with idea of energy levels
Changed to have protons that add up to the charge of the nucleus
James Chadwick proved the existence of neutrons
Half-life
Radioactivity is a Totally Random Process
Radioactive substance give out radiation no matter what
Can be measured with a Geiger-Muller tube and counter
Decay is entirely random
The time it takes for the amount of radiation to halve is the half-life
Half-life can be used to find the rate of decay
The Radioactivity of a Source Decreases Over Time
Each time a nucleus decays, the activity slows down
For some isotopes it's a matter of hours, some it's years
The activity never reaches zero
The half-life is the time taken for the number of radioactive nuclei in an isotope to halve :warning:
Can be described as the time taken for activity to fall by half