Naming Ionic Compounds

Understanding Ionic Compounds

Every atom is electrically neutral because its number of protons, which carry a positive charge, is equal to the number of electrons, which carry a negative charge. This balance ensures that the overall charge of the atom is zero.

However, most atoms can either gain or lose electrons, leading to a situation where the number of electrons differs from the number of protons. The charged particle that results from this imbalance is known as an ion.

Ionic compounds are created when ions with opposite charges form ionic bonds and create compounds. These compounds are made up of ions. The electron loss or gain of one atom is compensated by the electron loss or gain of another atom. This effectively means that one atom 'donates' an electron to the other atom it pairs up with.

Table of Contents

• Formulating Ionic Compounds
• Naming Ions
• Naming Ionic Compounds
• Common Questions

Formulating Ionic Compounds

1. Begin with the monatomic or polyatomic anion, followed by the cation.
2. The subscripts in the formula should result in an electrically neutral compound (i.e., the total positive charge should equal the total negative charge).
3. The subscripts should be the smallest set of whole numbers possible.
4. If the formula contains only one polyatomic ion, do not use parentheses. For example, write NaNO₃ instead of Na(NO₃).
5. If the formula contains more than one polyatomic ion, enclose the ion in parentheses and place the subscript outside the parentheses. For example, write Ca(OH)₂, Ba₃(PO₄)₂, etc.

Here are some examples:

Cation	Anion	Formula
Na+	Cl-	NaCl
Ca2+	Br-	CaBr2
Na+	S2-	Na2S
Mg2+	O2-	MgO
Na+	SO42-	Na2SO4
Cr3+	O-2	Cr2O3
NH4+	SO42-	(NH4)2SO4

Naming Ions

• The name of a monatomic cation is simply the name of the element followed by the word 'ion'.

For instance, Na⁺ is referred to as a sodium ion, Al³⁺ is an aluminium ion, Ca²⁺ is a calcium ion, and so on.

• Different elements can lose different numbers of electrons, leading to ions with different charges. For example, iron can form two cations: Fe²⁺ and Fe³⁺.

There are two ways to distinguish between these:

1. The charge of a positive ion is indicated by a Roman numeral in parentheses after the name of the element, followed by the word 'ion'. So, Fe²⁺ is referred to as the iron(II) ion, while Fe³⁺ is referred to as the iron(III) ion. This system is only used for elements that can form more than one common positive ion.

2. The second method uses two suffixes, -ic and -ous, attached to the stem of the name of the element. The -ic suffix is used for the higher of the two cation charges, and the -ous suffix is used for the lower. In many cases, the stem of the name of the element is derived from the Latin name for the element.

Element	Stem	Charge	Name
Iron	ferr-	2+	Iron (II) ion or ferrous ion
		3+	Iron (III) ion or ferric ion
Copper	cupr-	1+	Copper (I) ion or cuprous ion
		2+	Copper (II) ion or cupric ion

• The name of a monatomic anion consists of the stem of the name of the element, the suffix -ide, and the word 'ion'.

For example, F^- is a fluoride ion, Cl^- is a chloride ion, N^3- is a nitride ion, etc.

Naming Ionic Compounds

Binary Ionic Compounds Composed of a Metal and a Non-metal

A binary compound is a compound composed of two different elements. Each element may have more than one atom. A diatomic compound (or diatomic molecule) consists of two atoms, which may or may not be the same.

Ionic compounds are formed when metals combine with nonmetals. When naming binary ionic compounds, begin with the cation (and specify the charge if necessary), then name the nonmetal anion (using the stem of the element's name + -ide).

Do not use prefixes to indicate the number of each element present; this information is implied in the name of the compound.

For example:

Ionic Compounds with Polyatomic Ions

Ionic compounds are formed when metals combine with polyatomic ions.

The naming method for polyatomic ionic compounds is the same as for binary ionic compounds. The anion is named first, followed by the cation.

Do not use prefixes to indicate the number of each element present; this information is implied in the name of the compound.

For example:

Formula	Name
Ca(NO3)2	Calcium nitrate
(NH4)2SO4	Ammonium sulfate
NH4F	Ammonium fluoride
CaCO3	Calcium carbonate
Fe(OH)3	Iron (III) hydroxide or ferric hydroxide
Cr3(PO4)2	Chromium (II) phosphate
CrPO4	Chromium (III) phosphate