Percentage Composition Essay

Compounds were defined in Chapter 1 as pure substances that can be chemically separated into elements, although always with specific ratios. This observation is called the law of definite proportions. It was also observed that when elements combine to form compounds, the ratio may be different, depending on the type of compound. This is the law of multiple proportions. Both observations were explained by Dalton's atomic theory. This theory states that atoms, the smallest form of an element, combine in simple whole-number ratios to form molecules, the smallest form of a compound.

The expression that shows the number and kind of each atom in a molecule is the chemical formula. Chemical formulas use the chemical symbol of the atom to express the type of atom and a subscript following the symbol to express the number of atoms in the molecule. If there is only one of a type of atom, no subscript is used. In addition to the number and type of atom, chemical formulas can (but don't have to) suggest the arrangement of the atoms.

Each compound has not only a formula, but also a name. Like the formulas, the name of the compound must provide sufficient information to identify the number and type of each atom in a molecule. Therefore, systems for naming have been developed. The type of system depends on the type of compound. For binary molecular compounds, which are normally comprised of two types of nonmetal atoms, there is a prefix on the name of the element to express the number of that type of atom. If there is only one of that type of atom, no prefix is used. The second element has its ending changed to ide. For binary ionic compounds, usually comprised of a metal and a nonmetal, the cation, then the anion are named. Cations are simply the name of the element for group 1A and 2A metals. For other metals, the name of the metal is followed by its charge in parentheses. The charge is written as a Roman numeral. Monatomic (one-atom) anions change the end of the element...