Atoms, Ions and Compounds
It is easy to interpret a formula for an element or a compound, but it's a bit more complicated to
write the formula for a compound. How do you know what elements form the compound and in what proportion? To understand
how elements form compounds, an understanding of atoms and ions is essential.
Key Points to Remember:
1. All atoms are electrically neutral, except if they are ions
2. Ions are atoms that have gained or lost electrons
3. When writing formulas for compounds, the overall net charge must be zero, or if it's a polyatomic
ion, equal to the charge on the ion
4. If the compound contains a metal to a nonmetal, it is called an ionic bond and uses specific rules
for writing and naming the compounds
5. If the compound contains two nonmetals together, it is called a covalent bond and uses different
rules for writing and naming the compounds
Writing Formulas AND Naming Ionic Compounds
1. Use the first oxidation state listed on the periodic table for the nonmetal and metal
2. Bring them together placing the metal first and the nonmetal second
3. Equalize the charges by adding subscripts to the each of the ions
4. Polyatomic Ions are two or more covalently bonded atoms together that overall posess a net charge.
See the front of your reference table to find these. Use the overall net charge on the polyatomic ion when writing
formulas
5. To name, use the complete name of the metal ion; remove the -in ending from the nonmetal
ion and add -ide
6. If a metal has more than one oxidation state, use a roman numeral to indicate which ion
is to be used. For example, if the copper uses the +2 ion in a compound with Bromine, it would be called copper (II)
bromide
For Example
