Chemical element of an element to exist in one of many structural forms is known as 'allotropy'. The standard state, also known as the reference state, of an element is defined as its thermodynamically most stable state at a pressure of 1 bar and a given temperature (typically at 298.15 K). In thermochemistry, an element is defined to have an enthalpy of formation of zero in its standard state. For example, the reference state for carbon is graphite, because the structure of graphite is more stable than that of the other allotropes. Several kinds of descriptive categorizations can be applied broadly to
Element collecting element in everyday use. Some are averse to collecting the element as a compound or alloy, while others find this acceptable. Collectors may isolate elements in their own homes. Hydrogen, for example, can be easily isolated via the electrolysis of water. In addition to the element samples, some element collectors also collect items connected with the element, such as manufactured goods containing the element, rocks and minerals with the element as a constituent or compounds of the element. Some manufacturers also sell coins made from pure elements, and density cubes made from the pure element can also be sourced on