1.1 The International Union of Pure and Applied
Chemistry (IUPAC) is the body responsible for
naming compounds. It ensures the use of a
consistent, practical way of naming compounds that
allows scientists to communicate clearly and
1.1.1 There are many thousands of different ionic
compounds. Some have common names, such as
table salt. They also have chemical names that
reveal something about the elements in them. The
state of an element or compound is indicated by by
a subscript: (s) for solid, (l) for liquid, and (g) for gas.
The subscript (aq) stands for aqueous. This means
that the element or compound is dissolved in water.
22.214.171.124 The IUPAC system of naming ionic compounds is
very simple. All names of ionic compounds have two
parts, because all ionic compounds are made from
two parts. Every ionic compound is made up of a
cation (positive) and an anion (negative). The
naming rules work like this:
126.96.36.199.1 1. Name the cation first by using the elements
name. (It is usually the metal ion.)
188.8.131.52.1.1 2. Name the anion second by using the first part of
the elements name and changing the last part to
"-ide." (The anion is usually a non-metal ion.)
2.1 An electrically charged atom or group of atoms
3 Forming Ionic Compounds
3.1 Ionic compounds form when electrons transfer from one atom to another.
3.1.1 For example, sodium chloride, positively charged sodium ions are
attracted to negatively charged chloride ions. The two kinds of ions
group together in an organized array called a Crystal Lattice. The lattice
is made up of one sodium ion for every one chloride ion. Such a neutral
unit is called a Formula Unit.
184.108.40.206 An atom of sodium has one valence electron, and a chlorine atom has
seven valence electrons. When the two elements combine, the sodium
atom transfers an electron to the chlorine atom. As a result, both atoms
now have full outer energy levels. Remember that the most stable atoms
have full outer energy levels. When sodium transfers an electron to
chlorine, sodium's outer energy level is now full. When chlorine receives
the electron, its outer energy level is also now full. Both elements are
now stable as ions.
220.127.116.11.1 This type of bonding is called Ionic Bonding. Ionic bonds form between
atoms of metals and non-metals.
4 Common Properties of Ionic Compounds
4.1 Ionic compounds have many common properties. All of
them are solids at room temperature. They tend to
dissolve in water, although some dissolve much better
than others. Solutions of ionic compounds always conduct
5 Formulas for Ionic Compounds
5.1 The formula of an ionic compound contains element symbols that
identify each type of ion present. In some formulas, the symbols
are followed by subscript numbers that indicate the ratios of ions in
the compound. For example, the formula for BaF contains
subscripts. In BaF there is one barium ion for every two fluoride
ions.This represents the formula unit. The formula unit is the
smallest amount of a substance with the composition shown by
the chemical formula. It consists of positive and negative ions in
the smallest whole-number ratio that results in a neutral unit in the
crystal lattice of a compound. If there are no subscripts, assume
that the compound has one of each ion, so the ratio one to one in
the formula unit (e.g., NaCl ).
5.1.1 All ionic compounds are composed of an equal number of positive
and negative charges. This means the total charge of the cations
must equal the total charge of the anions. In some compounds, the
cation has a charge of 1+ and the anion has a charge of 1-. Recall
that this is because there has been a transfer of electrons between
the atoms. Consider sodium chloride. The sodium ion is Na and the
chloride ion is Cl . So only one ion of each element is needed to
make the positive and negative charges equal. The ratio of sodium
ions to chloride ions is one sodium ion to one chloride ion in a
formula unit. Therefore, the formula is NaCl. No subscripts are
needed because both ions have a charge of one.
18.104.22.168 Now consider the example of aluminium chloride, AlCl . All the
charges in the formula unit must be equal. So each aluminium atom
loses three electrons, and each chlorine atom gains one. The
aluminium ion has a charge of 3+. The chloride ion has a charge of
1-. Therefore, every one aluminium ion combines with three
chloride ions. The ratio is one cation (Al ) to three anions (Cl ), so
the formula is AlCl .
22.214.171.124.1 Steps for Writing Formulas for Ionic Copounds
126.96.36.199.1.1 1. Identify the ions and their charges.
188.8.131.52.1.1.1 2. Determine the total charges needed to balance.
184.108.40.206.220.127.116.11 3. Note the ratio of cations to anions.
18.104.22.168.22.214.171.124.1 4. Use subscripts to write the formula, if needed.
126.96.36.199.2 The Method of Lowest Common Multiple
188.8.131.52.2.1 The method of lowest common multiple is another way of determining
the correct formula for an ionic compound. First, find the lowest
common multiple of the charges for the two ions. Then divide by the
combining capacity of one ion to get the correct subscript for that ion.
Repeat the process for the other ion. This ensures that the number of
positive charges equals the number of negative charges, so the
formula unit is electrically neutral.
184.108.40.206.2.1.1 Steps for Using The Method of Lowest Common Multiple
220.127.116.11.18.104.22.168 1. Identify the ions and their charges: Ca is 2+, and N is 3-.
22.214.171.124.126.96.36.199.1 2. Find the smallest number that both charges will divide into.
For Ca and N it is 6.
188.8.131.52.184.108.40.206.1.1 3. Divide each charge into the lowest common multiple,and
write the numbers as subscripts: Ca: 6 ÷ 2 = 3 N: 6 ÷ 3 = 2.
The formula is Ca N .