Astrophysicists use the term "metal" to refer collectively to all elements in a star that are heavier than the lightest two, hydrogen and helium, and not just traditional metals. A star fuses lighter atoms, mostly hydrogen and helium, to make heavier atoms over its lifetime. Used in that sense, the metallicity of an astronomical object is the proportion of its matter made up of the heavier chemical elements.
Many elements and compounds that are not normally classified as metals become metallic under high pressures; these are formed as metallic allotropes of non-metals, for example, physicists were able to keep Hydrogen in its solid state under more than 3 million times the atmospheric pressure and deduce its metallic properties.
The strength and resilience of metals has led to their frequent use in high-rise building and bridge construction, as well as most vehicles, many home appliances, tools, pipes, non-illuminated signs and railroad tracks. Precious metals were historically used as coinage.
The elements which are considered as metals under ordinary conditions are shown in yellow on the periodic table below. The remaining elements are shown either as nonmetals or as metalloids of intermediate character.
The atoms of metallic substances are typically arranged in one of three common crystal structures, namely body-centered cubic (bcc), face-centered cubic (fcc), and hexagonal close-packed (hcp). In bcc, each atom is positioned at the center of a cube of eight others. In fcc and hcp, each atom is surrounded by twelve others, but the stacking of the layers differs. Some metals adopt different structures depending on the temperature.