Semiconductor Technology from A to Z

An element consists of many identical atoms (meaning atoms with the same number of protons, i.e. the same atomic number) and is a substance that cannot be broken down further by chemical means. The mass of an element is determined solely by the number of protons and neutrons, since the mass of the electrons is negligibly small. Hydrogen, with one proton and no neutrons, has a mass number of 1; the next heavier element, helium, has a mass number of 4 (2 protons + 2 neutrons). The mass number gives the number of particles in the nucleus. Multiplying it by the atomic mass unit u = 1.660·10^-27 kg gives approximately the mass of an atom – for helium, 6.64·10^-27 kg.

Chemical elements are usually named after the initial letters of their Latin or Greek names (hydrogen [H] from Latin hydrogenium, lithium [Li] from Greek lithos).

The periodic table of the elements arranges all chemical elements in order of increasing proton number (nuclear charge, atomic number), grouped according to their chemical properties into periods as well as main and subgroups.

The period indicates the number of electron shells, while the main group indicates the number of electrons in the outermost shell (1 to 8 electrons). Groups 1 and 2, as well as 13–18, form the main groups; groups 3–12 form the subgroups.

The first element with one shell (period 1) and one outer electron (group 1) is hydrogen, H. The next element, helium, He, has only one electron shell just like hydrogen and is therefore also in period 1. Since the first shell is already completely filled with two electrons, helium is not in group 2 but in group 18 (the noble gas group).

To accommodate further electrons, a new shell must be started. Lithium is therefore found in group 1, period 2 (two electrons in the first shell, one valence electron in the second shell). A shell can hold a maximum of 2n² electrons, where n stands for the period.

After the first two valence electrons in the outermost shell have been filled in groups 1 and 2, starting from the fourth period further inner shells are first completed with electrons before the outermost shell is fully filled with electrons across groups 13 to 18.

The Periodic Table of the Elements

Important elements in semiconductor technology

Elements on the left side of the periodic table are metals. These tend to give up valence electrons in order to reach a stable electron configuration (the noble gas configuration). On the right side of the periodic table are the nonmetals, which take up additional electrons to reach the noble gas configuration. Between them are the metalloids, such as silicon and germanium.