Formation of Ionic Compounds

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Formation of Ionic Compounds

ionic compounds: compounds composed of cations and anions

they’re usually composed of metal cations and nonmetal anions

*Although they are composed of ions, ionic compounds are electrically neutral

The total positive charge of the cations equal the total negative charge of the anions

Ionic Bonds

ionic bonds: the electrostatic forces that hold ions together in ionic compounds
The charges must be balanced: the positive charge must equal the negative charge
You have to switch the charges:

For example: bromine and aluminum

Br ^1—and Al³⁺
Switch them so it becomes: Br₃Al

Formula Units

chemical formula: shows the kinds and numbers of atoms in the smallest representative unit of a substance

Chemists represent the composition of substances with chemical formulas

formula unit: the lowest whole-number ratio of ions in an ionic compound

for sodium chloride, formula unit is NaCl and the lowest whole-number ratio of ions is 1:1 (one Na⁺ to each Cl^—)
for magnesium chloride, the formula unit is MgCl₂ and the lowest whole number ratio is 1:2 (one Mg²⁺ for every 2 Cl^—)
for aluminum bromide, the lowest ratio is 1:3 (one Al³⁺ to three Br^—) so the formula unit Is AlBr₃

Properties of Ionic Compounds

Ionic compounds are crystalline solids at room temperature

Ions are arranged in repeating 3-dimensional patterns
The coordination number is the number of ions of opposite charge that surround the ion in a crystal
For example, composition of NaCl is typical

each sodium ion is surrounded by 6 chloride ions
each chloride ion is surrounded by 6 chloride ions
the anion and cation in NaCl have a coordination number of 6
large attractive forces keep the structure stable

Ionic compounds have high melting points
Ionic compounds can conduct an electric current when melted or dissolved in water

When ionic compounds are melted or dissolved, the orderly crystal structure breaks down and cations and anions are free to move around
this movement allows electricity to flow

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