Structures and Bonding: Ionic Bonding

Ionic bonding occurs between metals and non-metals. It involves the transfer of electrons from the metal atom to the non-metal atom.
In ionic bonding, the metal atom loses electrons to become a positively charged ion (cation) and the non-metal atom gains these electrons to become a negatively charged ion (anion).
This transfer of electrons is driven by the desire of both atoms to achieve a stable electron configuration, typically that of a noble gas.
After the transfer, the oppositely charged ions attract each other due to electrostatic forces, leading to an ionic bond forming. The resulting compound is known as an ionic compound.
Ionic compounds have high melting and boiling points, as the electrostatic forces requiring large amounts of energy to overcome. This makes them generally solid at room temperature.
These compounds can also conduct electricity, but only when either dissolved in water or in a molten state. When they are in these states, the ions are free to move and carry charge.
The 3-D structure formed by an ionic compound is known as a crystal lattice. This structure results from ions arranging themselves to maximise attraction and minimise repulsion.
Crystal lattice structures are extremely strong due to the many ionic bonds. This leads to properties such as brittleness - under certain types of stress, the layers of ions can shift in a way that ions of same charges overlap, and the resulting strong repulsion causes the lattice to shatter.
Remember, a single ionic bond does not exist in isolation. In an ionic crystal, each ion is attracted to many ions of opposite charge. This means we often refer to ionic bonding rather than individual ionic bonds.
Writing of ionic compounds is best achieved using formulae. For example, sodium chloride is NaCl, capturing the one-to-one ratio of sodium ions to chloride ions.
Also noteworthy is the conservation of charge in ionic compounds. The total positive charge from the cations must equal the total negative charge from the anions.
Examples of commonly encountered ionic compounds include table salt (sodium chloride, NaCl), limestone (calcium carbonate, CaCO3), and baking soda (sodium bicarbonate, NaHCO3).