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5.2 identify that isotopes of some elements may be unstable and emit radiation
identify that isotopes of some elements may be unstable and emit radiation
- Isotopes are different forms of the same element. Most occur naturally and some are manufactured. Isotopes of an element have the same number of protons and electrons but a different number of neutrons in the nucleus. i.e. they have a different mass number.
Mass number = number of protons + number of neutrons.
- Isotopes of oxygen, for example, have all eight protons but 16O has eight neutrons while 18O has ten neutrons. The superscript before the symbol for the atom designates which isotope of the element is present. It might also be written as oxygen-16 or oxygen –18.
- The additional number of neutrons in the nucleus makes some isotopes unstable and the particles in the nucleus change until they reach a more stable state. If the isotope decays by α decay, two protons and two neutrons (a helium nucleus) are emitted from the nucleus. If the isotope decays by β decay then a neutron changes to a proton + an electron and the electron leaves the nucleus. Geiger Counters or Liquid Scintillation Counters can detect both types of particles.