Page "Chemical element" Paragraph 6

When two distinct elements are chemically combined, with the atoms held together by chemical bonds, the result is termed a chemical compound.

Two thirds of the chemical elements occur on Earth only as compounds, and in the remaining third, often the compound forms of the element are most common.

Chemical compounds may be composed of elements combined in exact whole-number ratios of atoms, as in water, table salt, and minerals as quartz, calcite, and some ores.

However, chemical bonding of many types of elements results in crystalline solids and metallic alloys for which exact chemical formulas do not exist.