Tuesday, 31 December 2013

Ionic compounds and molecules

Ionic compounds

Metals and non-metals form ionic compound.
An ionic compound is formed by the transfer of electrons from metal to non-metal.
Metals lose electrons to form positively charged ions (cations).
Non-metals gain electrons to form negatively charged ions (anions).

Covalent Molecules
Non-metals combine together to form covalent molecules.
A covalent molecule is formed by the sharing of electrons between atoms.

Ionic compounds
Simple molecules
High melting and boiling point, and are solids at room temperature.

Oppositely charged ions are held together by strong electrostatic force of attraction. Large amount of energy is required to overcome these forces of attraction, resulting in high melting and boiling point (hence they exist as solid at room temperature).
Low melting and boiling point (are liquid or gas at room temperature).

Molecules are held together by weak intermolecular forces of attraction. Little energy is needed to overcome this energy, resulting in low melting and boiling point (hence they exist as liquid or gas at room temperature).
Cannot conduct electricity in solid state.

Ions are held together and are not free to move about to conduct electricity.
Cannot conduct electricity in all states.

There are no free moving electrons.
Conduct electricity in aqueous or molten state.

Ions are free to move about to conduct electricity.
Most ionic compounds are soluble in water, but insoluble in organic solvents.
Most simple molecules are soluble in organic solvent but insoluble in water.
Table showing the differences in properties between ionic compounds and simple covalent molecules


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