Bonding

Bonding

Atoms of elements combine with other atoms in order to achieve a full outer shell of electrons. When atoms combine, a chemical bond forms between them. There are three types of bond: ionic, covalent and metallic.

(1) Metals lose electrons to form an ionic compound

(2) Non-metals gain electrons

(3) Non-metals share electrons

Remember that:

• Metal + Non-metal = Ionic Compound
• Non-metal + Non-metal = Covalent Compund
• Metal+ Metal = Metallic Compound

An ionic bond is formed between a metal and a non metal. The metal will transfer an electron(s) to the non-metal. The metal forms a positive ion and the non metals forms a negative ion. The attraction between the two is very strong and is called an electrostatic attraction.

Transition Metals in Ionic Compounds

Transition metals can form an ionic bond with non metal atoms. The transition metal will lose an electron(s). Unlike other metals, transition metals do not follow a set rule of how many electrons they lose. The number of electrons the transition metal will lose is given by the name of its compound in Roman Numerals or we can work it out in the formula.

Polyatomic Ions

There are ions that contain more than one atom in one unit. For example, Sulphate (SO42-). If we need more than one unit of a polyatomic ion we must include brackets around the units. For example, Na2SO4 (one unit of SO4), Al2(SO4)3 (three units of SO4)

Properties of Ionic Compounds

Ionic compounds form giant (indefinite particle number) lattice (regular arrangement of particles) structures. The arrangement of the particles (ions) in an ionic structure can be used to explain the properties of ionic compounds.

Properties of Ionic Compounds Include:

• high melting and boiling points because of indefinite number of strong ionic bonds
• the crystals are hard because the ions are locked in a fixed position
• however, they are brittle because if pressure is applied, ions of the same charge are forced together and so they repel and the crystal breaks easily
• they dissolve in water (water is a polar solvent)
• they conduct electricity when they are molten or dissolved in a solution because the ions are free to move around
• they cannot conduct electricity when solid because the ions cannot move so a current can't pass through the solid.

Covalent Compounds

A covalent compound forms when two non-metal atoms combine. When a covalent bond forms, electrons are shared between atoms to achieve a full outer shell. This is different to an ionic bond…