Bonding

Nature of the Chemical Bond

Essential Information

• Everything around us is made up of atoms• There are over 100 different kinds of atom

(109 known to date)• Atoms are placed into a particular order on

the Periodic Table of the Elements.• In different combinations, atoms make up

every single substance in the Universe….• E.g. wood, plastic, metals, oxygen etc

Water

• This is perhaps the most familiar substance on Earth.

• Write down the structural formula for water.

• In order for these substances to exist at all, the atoms must be attracted and combined with each other in some way.

• i.e. they must be held together by some force.

• The forces holding atoms together are called………………

• Chemical bonds

Chemical Bonds

There are 3 types of chemical bonding at the atomic level:

(i) Ionic bonding

(ii) Covalent bonding

(iii) Metallic bonding

The Ionic Bond A particular form of bonding which

usually involves the combining of a metal atom with a non-metal atom.

•  Example: Sodium chloride.• Should know that inert gas configuration is

particularly stable due to full outer shell.• Therefore atoms of other elements need to

gain or lose electrons in order to gain an i.g.c.

• Elements to the left hand side of a Periodic Series have few electrons in their outermost shells

• Therefore tend to lose electrons.

• Elements to r.h.s. of a Periodic Series have several electrons in their outer shells

• Therefore tend to gain electrons.

Sodium Chloride (NaCl)• The most familiar example of a compound

with ionic bonding.

• Electronic configurations are…..

• Na 1s2 2s2 2p6 3s1. Cl 1s2 2s2 2p6 3s2 3p5

• The sodium atom has one more electron than the noble gas………….

• The chlorine atom has one less electron than

………………… .

• The sodium atom loses its outer shell electron to form a positively charged ion, with an electronic configuration of ……….. .

• The chlorine atom gains an outer shell electron to form a negatively charged chloride ion, with a configuration of …….. .

• i.e Na Na+ + e-

atom

• Cl + e- Cl-

Sodium Chloride Lattice• The oppositely charged sodium and

chloride ions attract each other and are held together by strong electrostatic forces.

• They form a giant ionic lattice.

• This type of bonding is called ionic bonding.

• Draw ’space filling model’ for NaCl .

Evidence for the Structure of Materials

• X-Ray Diffraction

• See homework

Properties of Ionic Substances

• Electrostatic bonds between ions very strong.• (Each sodium ion in the NaCl lattice is surrounded

by 6 chloride ions, and each chloride ion is surrounded by 6 sodium ions).

• Therefore ions very difficult to separate .• Crystalline• Therefore high melting and boiling points. 

• Lattice can be disrupted by water

• Water molecules are attracted to the charges of the ions.

• Water molecules surround the ions and break up the lattice

• We see this as the crystal dissolving. (see OHT).

• When molten, or in solution, ionic solids conduct electricity (but not as solids because ions are in fixed lattice positions and can't move).

• This is because positive and negative ions can move to oppositely charged electrodes, where they are discharged (electrolysis).