What Are Isotopes?
Our world is made up of around 90 elements such as hydrogen, helium, and lithium. Look closely at any one element and you will find a nucleus made up of protons and neutrons, surrounded by electrons. A hydrogen atom contains one proton while a helium atom contains two, and so on. The number of protons in the nucleus is what differentiates elements from one another. But it is also understood that within a single element there can be a different number of neutrons as well. For any one element, of course, the number of protons is always the same, but with more neutrons the element will be heavier. Each of these forms of a single element—which contain the same number of protons but a different number of neutrons—is called an isotope. Isotopes can be found in the semiconductors we discussed earlier. Germanium (Ge), for example, has five naturally occurring isotopes with mass numbers (number of protons + number of neutrons) of 70, 72, 73, 74, and 76. Silicon, on the other hand, has just three stable isotopes, numbered 28, 29, and 30.