Complete the statement.
Silicon is ().

 - an elementary substance
 - a compound
You can tell whether silicon is an elementary substance or a compound by counting the number of atomic symbols in its chemical formula. An atomic symbol consists of either one capital letter or a capital letter followed by one or two lowercase letters.
The chemical formula for silicon contains one atomic symbol: Si. So, the formula tells you that silicon is composed of only one chemical element.
Since silicon is composed of only one chemical element, silicon is an elementary substance.