Final answer:
Cobalt, represented by the symbol Co, is an element because it consists of single, uncombined atoms and cannot be reduced to simpler substances. Compounds like carbon monoxide (CO) contain two different elements, while cobalt can also form ions with specific charges, such as Co2+ for the cobalt(II) cation.
Step-by-step explanation:
Cobalt is known to be an element because it is a pure substance that cannot be broken down into simpler substances by chemical means. The symbol for cobalt is Co, which represents a single atom of the element. This can be contrasted with a compound, which consists of two or more elements that are chemically combined in a fixed ratio. For instance, CO represents carbon monoxide, a compound made up of carbon (C) and oxygen (O).
When discussing ions of cobalt, we see variations such as cobalt(II) cation, indicated by a 2+ charge. Ions are atoms or groups of atoms that have gained or lost electrons, resulting in a net charge. For example, the cobalt(II) ion (Co2+) indicates a cobalt atom that has lost two electrons. The valency or oxidation state of ions is specified when there are multiple common charges for an element, as with cobalt that can also have a 3+ charge, resulting in the cobalt(III) ion.
Furthermore, cobalt can form various compounds, such as cobalt(II) chloride hexahydrate, with the formula CoCl₂·6H₂O, where 'Co' symbolizes the cobalt element within that compound.