alkalis (
51Electron shell — Periodic table with electron shells An electron shell may be thought of as an orbit followed by electrons around an atom s nucleus. The closest shell to the nucleus is called the 1 shell (also called K shell ), followed by the 2 shell (or L shell …
52Exothermic — In thermodynamics, the word exothermic outside heating describes a process or reaction that releases energy usually in the form of heat, but it can also release energy in form of light (e.g. explosions), sound, or electricity (e.g. a battery).… …
53Glass — This article is about the material. For other uses, see Glass (disambiguation). Moldavite, a natural glass formed by meteorite impact, from Besednice, Bohemia …
54Hafnium — lutetium ← hafnium → tantalum Zr ↑ Hf ↓ Rf …
55History of medicine — All human societies have medical beliefs that provide explanations for birth, death, and disease. Throughout history, illness has been attributed to witchcraft, demons, astral influence, or the will of the gods. These ideas still retain some… …
56Niobium — zirconium ← niobium → molybdenum V ↑ Nb ↓ Ta …
57Organic chemistry — Structure of the methane molecule: the simplest hydrocarbon compound. Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, composition, reactions, and preparation (by synthesis or by… …
58Platinum — This article is about the chemical element. For other uses, see Platinum (disambiguation). iridium ← platinum → gold Pd ↑ Pt ↓ Ds …
59Ruthenium — (pronEng|ruːˈθiːniəm) is a chemical element that has the symbol Ru and atomic number 44. A rare transition metal of the platinum group of the periodic table, ruthenium is found associated with platinum ores and used as a catalyst in some platinum …
60Silicon — Not to be confused with the silicon containing synthetic polymer silicone. aluminium ← silicon → phosphorus C ↑ Si ↓ Ge …
