ionic+compounds


 * Naming Ionic Compounds**

To name ionic compounds, one must ask some important questions:
 * 1) Is there a metal present? If so, never use prefixes, for those are only used in covalent compounds.
 * 2) What type of metal is it, Type I or Type II? If it is a Type II, then you must use its proper roman numeral in the name.
 * 3) Is there a polyatomic ion present? If there is, be sure to use its proper name, not the names of the individual atoms.

Naming ionic compounds is as easy as writing the name of the ions in the order they appear.

For example, KBr is simply potassium bromide.

And LiOH is lithium hydroxide.

Just remember to use the "ide" endings, or to identify the proper polyatomic ion.

The only catch is when the metal is a type (II) ion, which requires you to use the correct charge and report it in parentheses.

Example: FeO versus Fe 2 O 3.

In FeO, write the obvious names first, leaving the roman numeral for last: iron ( ? ) oxide.

For Fe 2 O 3, it would be iron ( ? ) oxide as well.

To determine which iron is used in each, figure out the total negative charge in each.
 * FeO has one oxygen, so it has a 2- charge.
 * the iron must be equal but opposite, so it has a 2+ charge.
 * FeO is therefore named iron (II) oxide.


 * Fe 2 O 3 has three oxygens: 3 x (2-) = -6 total.
 * The irons must be equal but opposite = +6 total.
 * Because there are two irons, divide +6 by 2 to get +3. Each iron is +3.
 * Fe 2 O 3 is therefore iron (III) oxide.

Try these practice worksheets:


 * Constructing Ionic Compounds**

Metal and nonmetal ions combine to form ionic compounds. A neutral ionic compound will have a balanced charge between the cation (+) and the anion (-). For example, the magnesium ion will combine with two chloride ions in a 2:1 ratio:

magnesium chloride:
 * magnesium is a 2+ ion: Mg 2+
 * chloride is a 1- ion: Cl-
 * combined, there must be two chloride ions (two negatives) to balance the 2+ charge on magnesium: MgCl2 is its formula.

For ions with polyatomics, parentheses are used if two numbers are next to one another.
 * example: copper (II) nitrate
 * copper (II) is Cu2+
 * nitrate is NO3-
 * combined, they have the formula Cu(NO3)2

The goal is to combine the two ions so that they have equal but opposite (+) and (-) charges.

One quick method that is nearly fool-proof is to "swap" ionic charges. Take aluminum oxide as an example:
 * aluminum has a 3+ charge; oxygen has a 2- charge;
 * swap them so aluminum gets the 2, and oxygen gets the 3;
 * write their new numbers subscript: Al 2 O 3.

The swap method works every time, if you remember these points:
 * use parentheses around polyatomics
 * don't ever change existing subscript numbers in polyatomics (they keep their identities)
 * reduce mathematically if you can: example, Ca 2+ and CO 3 2- makes CaCO 3.

Watch this powerpoint on the swap method.