2.5 Chemical Bonding (Sec 7.2 pg 176 – 181)

The physical forces that join or connect atoms together are called chemical bonds. Remember: BONDING involves interactions b/w the ELECTRONS of 2 or more atoms. There are 2 general types of bonding (ionic and covalent):

Oppositely charged ions (metals and non-metals) have a strong attraction for one another and, as a result, are held tightly together. This is known as ionic bonding and serves to build atoms into compounds called ionic compounds. In ionic bonding, a transfer of valence e occurs. Ionic bonding always occurs b/w metals and non- metals

Some properties of ionic bonds: – Form crystals (See Fig.2 p.177) – Have high melting points (LOTS heat needed to separate tightly bound ions) – Hard and brittle – Conduct electricity when dissolved in water.

Another type of bonding occurs when non-metals ‘share’ their valence e with other non-metals to complete their valence shells. This bonding is called covalent bonding and builds atoms into covalent or molecular compounds. Therefore, in covalent bonding, a sharing of valence electrons occurs (always b/w 2 non-metals).

Some properties of covalent bonds: – Form crystals – Do not conduct electricity when dissolved (please see Fig.9 p.181) – Have low melting and boiling points.

Covalent bonding can explain the existence of diatomic elements (please see Fig.4&5 p.178)

The third kind of bond is a cross between the ionic bond and the covalent bond. It is called the polar covalent bond and it forms when the two elements share valence electrons but one element pulls the electrons closer to its nucleus.

The diagram on the right shows the breakdown of pure substances:

Atoms are the smallest unit of elements (in chemistry…) Ions are the smallest unit for ionic compounds. Molecules are neutral particles that consist of 2 or more atoms covalently bonded together (Fig.6 p.178) – they form molecular compounds