Isotopes
Physics: AQA A Level, topic 2.1.4
Isotopes
Atoms of the same element always have the same number of protons (i.e. same atomic number). But, atoms of the same element can have different numbers of neutrons. We call these isotopes. Hydrogen has three isotopes:
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Protium
- Protium is a hydrogen atom with 1 proton and 0 neutrons.
- 99.98% of hydrogen atoms are protium.
- It is used in hydrogen fuel cells and the production of plastics.
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Deuterium
- Deuterium is a hydrogen atom with 1 proton and 1 neutron.
- Around 0.02% of hydrogen atoms are deuterium.
- It is used in nuclear fusion.
Tritium
- Tritium is a hydrogen atom with 1 proton and 2 neutrons.
- It is very rare.
- It is used in thermonuclear fusion weapons.
Nuclides
A nuclide is a type of isotope.
Definition of a nuclide
- A nuclide refers to a specific nucleus that contains a certain number of protons and neutrons.
Example
- A carbon nuclide with 6 protons and 6 neutrons is different to a carbon nuclide with 6 protons and 7 neutrons. But, both are isotopes of carbon.
Carbon Dating
We can use our knowledge of isotopes to calculate the age of fossils.
Radioactive carbon-14
- All living organisms have the same amount of carbon-14 atoms as a percentage of all carbon isotopes.
- Once the organism dies, it no longer absorbs carbon from the atmosphere.
- Carbon-14 is radioactive and so will decay over a known half life.
- So, the older a fossil is, the fewer carbon-14 isotopes it will contain and the less radiation it emits.
Test yourself on Isotopes
Isotopes of hydrogen
Protium contains 0 neutrons and tritium contains 2 neutrons. How many more neutrons does tritium have than protium?
Which of the following is NOT a naturally occurring isotope of carbon?
Carbon Dating
Explain how radioactive carbon-14 can be used to find the age of a fossil.