Chemical Bonding

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Covalent Bonds

Is the sharing of electrons between the nuclei of atoms.

Form between atoms of non-metals

Covalent bonds form when electrons are shared between two atoms.

Covalently bonded substances is called a molecule.

Single covalent bonds

Forms when each atom shares one electron and attains a noble gas structure.

Double covalent bonds

Involves two pairs of electrons.

Triple covalent bonds

Forms when there are three shared pairs of electrons

We can represent covalent bonds by using the Cooper structure or the Lewis structure

Relative molecular mass of a covalent compound

The relative molecular mass(Mr) is equal to the sum of all the relative atomic masses of the atoms present in the molecule.

E.g. calculate relative molecular mass of ammonia (NH3)

Mr(NH3)= Ar(N) + 3Ar(H)

=14,0 + (3 X 1,01)

=17,03

Ionic Bonding

Ionic bonds are form between a metal to a non- metal.

Electrons are transferred forming ions.

These exert an electrostatic force of attraction on each other.

Formation of ionic bonds

Ions are formed by the loss or gain of electrons.

When an atom forms an ion, the electron structure becomes that of the noble gas closest to it.

Ions tend to be stable like noble gasses and do not react with other molecules.

Formation of an ionic crystal lattice

Formation of positive ions are always coupled with the formation of negative ions.

Metal lose electrons forming positive ions, non-metals gain these electrons forming negative ions.

The positive metal ions then attract the negative non-metal ions forming ionic bonds.

Ion Pairs

A pair of ions that bond do not form a molecule but an ion pair.

They form compounds made up of ion-pairs.

Ionic Bonds between metal atoms and compound ions

Compound or polyatomic ions form stable groups of atoms which carry a charge.

Groups of atoms as a whole acts as charged particles in forming an ionic compound with an oppositely charged ion.

Relative Formula Mass of an ionic compound

The relative formula mass is equal to the sum of the relative atomic masses of atoms in the chemical formula.

****Just add all the relative atomic masses for the atoms that make up formula of compound*****

E.g. calculate relative formula mass of aluminum sulfide (Al2S3)

Metallic Bonding

formed when a delocalized electron is shared among positive ions in a metal.

Bonding in Metals

Atoms from the same metals form metallic bonds.

The valence electrons become detached from the atom and roam freely through the metal.

Atoms become positive ions as electrons move away causing a net deficiency of electrons around each atom.

By saying the valence electrons are delocalized means that they belong to positive ions in the metal lattice.

No valence electrons belong to a specific atom.

Metals form giant structures of many metal atoms as the electrons and positive ions have strong attractive forces between them.

Metallic bonds and properties of metals

1) Conduction of heat and electricity

2) Malleability and ductility

3) High density

4) Metallic luster

Alloys

Formed when different metals are melted and mixed.

This includes:

1) Stainless steel

2) Brass

3) Sterling silver

Covalent bonding

Ionic bonding

Metalic bonding