Stable and unstable nuclei
The balance of Subatomic particle with a positive charge and a relative mass of 1. The relative charge of a proton is +1. and Uncharged subatomic particle, with a mass of 1 relative to a proton. The relative charge of a neutron is 0. in a The central part of an atom. It contains protons and neutrons, and has most of the mass of the atom. The plural of nucleus is nuclei. determines whether a nucleus will be stable or unstable.
Too many neutrons or protons can upset this balance making the nucleus unstable.
Elements with fewer protons, such as the ones near the top of the periodic table, are stable if they have the same number of neutrons and protons.
For example carbon, carbon-12 is stable and has six protons and six neutrons.
However as the number of protons increases, more neutrons are needed to keep the nucleus stable.
For example lead, lead-206 has 82 protons and has 124 neutrons.
Nuclei with too many, or too few, neutrons do exist naturally but are unstable and will disintegrate (or decay) by emitting radiation.
This is called radioactive decay.
It is important to realise that radioactive nuclei disintegrate:
- spontaneously;
- and randomly.
This means that the process of radioactive decay can not be speeded up or slowed down by artificial means (spontaneous decay).
It also means that we cannot tell when a particular unstable nucleus will decay (random decay).
Key points
- Some nuclei are unstable.
- They disintegrate, emitting radiation randomly, and spontaneously.
- Such nuclei are described as radioactive.