Physical properties of ionic compounds
The ions in a compound such as sodium chloride are arranged in a lattice structure. This regular arrangement results in the formation of a crystal.
The diagram shows part of the crystal lattice of sodium chloride:
Positively charged Na ions, negatively charged Cl ions
This pattern is repeated in all directions, giving a giant three-dimensional lattice structure in sodium chloride crystals.
Because of the strong electrostatic forces between them, it takes a great deal of energy to separate the positive and negative ions in a crystal lattice. This means that ionic compounds have high melting points and boiling points.
Solid ionic compounds do not conduct electricity, because the ions are held firmly in place. They cannot move to conduct the electric current. But when an ionic compound melts, the charged ions are free to move. Molten ionic compounds do conduct electricity.
When a crystal of an ionic compound dissolves in water, the ions separate. Again, the ions are free to move, so a solution of an ionic compound in water also conducts electricity.
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Properties of ionic compounds - Higher
Positively charged Na ions and negatively charged Cl ions
Ionic bonds form when a metal reacts with a non-metal. Metals form positive ions and non-metals form negative ions. Ionic bonds are the electrostatic [electrostatic: An electrostatic force is generated by differences in electric charge (ie positive and negative) between two particles. It can also refer to electricity at rest. ] forces of attraction between oppositely-charged ions.
The oppositely-charged ions are arranged in a regular way to form giant ionic latticeslattice: A lattice is a regular grid-like arrangement of atoms in a material.. Ionic compoundscompounds: Substances formed by the chemical union (involving bond formation) of two or more elements. often form crystals as a result. The illustration shows part of a sodium chloride (NaCl) ionic lattice.
Properties of ionic compounds
High melting and boiling points - ionic bonds are very strong and a lot of energy is needed to break them, so ionic compounds have high melting points and boiling points.
Conductive when liquid - ions are charged particles, but ionic compounds can only conduct electricity if their ions are free to move. So ionic compounds do not conduct electricity when they are solid, but they do conduct electricity when they are dissolved in water or when they are melted.
Examples of ionic compounds
|Element and symbols||Properties|
Sodium chloride, NaCl
High melting point - 800°C
Non-conductive in its solid state, but when dissolved in water or moltenmolten: Molten means reduced to liquid form by heating. It is mainly used to describe rock, glass or metal., NaCl will conduct electricity.
Magnesium oxide, MgO
Higher melting point than sodium chloride - around 2,800°C. This is because its Mg2+ and O2- ions have a greater number of charges, and so form stronger ionic bonds, than the Na+ and Cl- ions in sodium chloride.
Because it stays solid and unconductive at such high temperatures, magnesium oxide is used for high-temperature electrical insulation.
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