The existence of isotopes was first suggested by the English radiochemist Frederick Soddy in 1912 ....…
Isotopes are variants of a particular chemical element. Each element has a given number of protons and electrons, but each isotope has a different number of neutrons. The existence of isotopes was first suggested by the English radiochemist Frederick Soddy in 1912, while he was a lecturer at the University of Glasgow. The term isotope, Greek for “at the same place,” was coined by Margaret Todd, a Scottish physician and family friend of Soddy, during a dinner in Glasgow, when Soddy explained that different isotopes of a single element occupy the same position on the periodic table.
The number of nucleons (protons and neutrons) in the nucleus is the mass number, and each isotope of a given element has a different mass number. For example, carbon-12, carbon-13 and carbon-14 are three isotopes of the element carbon with mass numbers 12, 13 and 14, respectively. The atomic number of carbon is 6, which means that every carbon atom has 6 protons. Carbon-12 has six neutrons and therefore a mass number of 12 (6 protons + 6 neutrons), carbon-13 has 7 neutrons (13=6+7) and carbon 14 has 8 neutrons (14=6+8).
By studying a sample (e.g. rock or fossil) scientists can use the ratio of isotopes (e.g. helium 3 to helium 4) to determine key indicators such as the age of the sample.