Naming Ionic and Molecular
Compounds

Naming Compounds
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Helps get rid of the confusion that can result from inaccurately naming compounds
• Example: black board chalk and the chalk in
TUMS
Naming compounds also shows the importance of using names that provide information about the chemical composition of a substance
The International Union of Pure and
Applied Chemistry (IUPAC) is the body responsible for naming compounds.

Ionic Compounds
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• Example: Sodium Chloride (NaCl) “ table salt ”
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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 such sodium ion for every one chloride ion
Such a neutral unit is called a formula unit

Ionic Compounds

Ionic Compounds
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Recall that an atom of sodium has 1 valence electron and a chlorine atom has 7 valence electrons
When the two combine the sodium atom transfers one electron to the chloride atom
• As a result, both atoms now have full other energy levels (they are stable)
• This type of bonding (the transfer of electrons) is called ionic bonding
• Ionic bonds form between metals and non-metals

Ionic Compounds

Ionic Bonding

Ionic Compounds
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• Solid at room temperature
• Dissolve in water
• Solutions if ionic compounds conduct electricity

Ionic Compounds
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There are thousands of Ionic Compounds
Several have common names
They also have chemical names
• See table A2.2 on page 41
The state of an element or compounds is indicated by a subscript: (s) for solid, (l) for liquid, (g) for gas and (aq) for aqueous
• Aqueous is a compound or element dissolved in water

Naming Ionic Compounds
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All names of ionic compounds have 2 parts
• Every ionic compound is made up of a cation and an anion
The naming Rules work like this:
1. Name the cation first by using the element ’ s name. (it is usually a metal ion)
2. Name the anion second by using the first part of the element ’ s name and changing the last part to “ -ide ” (it is usually a non-metal ion)

Formula Cation Anion Name
NaCl
(s)
BaF
2(s)
K
3
N
(s)
Na +
Ba 2 +
K +
Cl -
F -
N 3-
Sodium
Chloride
Barium fluoride
Potassium
Nitride

Formulas for Ionic Compounds
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Contain element symbols that identify each type of ion present
In some formulas, the symbols are followed by subscript numbers that indicated the ratio of ions in the compound
• For example in BaF
2(s) there is one barium ion for every two fluoride ions
• This represents the formula unit (the smallest amount of the substance with the composition shown by the chemical formula)

Formulas for Ionic Compounds
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• Na + and Cl , both charges cancel one another out and therefore there is an equal number of positive and negative charges

Formulas for Ionic Compounds
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All ionic compounds are composed of an equal number of positive and negative charges. Cations = Anions
Example: AlCl
3
• Each aluminium atom loses 3 electrons and each chloride atom gains 1
• The aluminium ion has a charge of 3+ and the chloride ion has a charge of 1-
• Therefore, every one aluminium ion combines with three chloride ions
• The ration is one cation (Al 3+ ) to three anions (Cl ) and thus the formula, AlCl
3
• See next slide with table

Formulas for Ionic Compounds
Steps Examples
1. Identify the ions and their charges
2.Determine the total charges needed to balance
3. Note the ratio of cations to anions
Sodium chloride
Sodium: Na +
Chloride: Cl -
Na + :1
Cl :1
1 to 1
Aluminium chloride
Aluminium: Al 3+
Chloride: Cl -
Al 3+ :3
Cl :1+1+1=3
1 to 3
4.Use subscripts to write the formula, if needed
NaCl AlCl
3

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• 1 st , find the lowest common multiple of the charges for the 2 ions
• 2 nd , divided by the combining capacity of one ion to get the correct subscript for that ion
• Example on board (copy)