When only one pair of shared electrons is involved in a covalent bond, the linkage is called a bond.

When only one pair of shared electrons is involved in a covalent bond , the linkage is called a single bond.

in theory, limestone is composed principally of the compound calcium carbonate - caco3, but in reality this compound is deposited in conditions involving a number of other compounds as impurities so it ends up being a mixture of many compounds.

hope this : -)

tony (lordcaos066)