CHEMICAL BONDING Covalent Bonding

How to play my game?

Some queries..

Physical Properties of Ionic compounds Solubility

How it happens? Electrical conductivity

Why do ionic compounds only conduct electricity in the molten or aqueous state?

Overview

Bonding Ionic Covalent MetallicStructure Giant

ionicSimple

molecularGiant

covalentGiant

MetallicExample Sodium

chlorideWater Diamond Iron

Bonding and structure explains the properties of a substance!

Compare and Contrast

Ionic VS Covalent

Similarities Octet Rule: Electronic configuration of a noble gas

(PS: Everybody wants to be noble!!)

Differences

Ionic Bond Covalent BondBetween positive ions of metals and negative ions of non-metals

Between non-metal atoms

Electrons are transferred Electrons are shared

What to do??

Covalent Bonding

Covalent Bond: The Definition

A covalent bond is…

a bond formed by the sharing of a pair of electrons.

More about COVALENT BONDING

Each atom acquires a stable octet structure Electronic configuration of noble gas (Full shell) =

Energetically stable

Formed between atoms of non-metals (but there are exceptions!) “Spectrum” of bonds

Covalent Compounds of ELEMENTS Hydrogen, H2 (Single covalent bond)

Covalent Compounds of ELEMENTS Chlorine, Cl2 (Single covalent bond)

Covalent Compounds of ELEMENTS Oxygen, O2 (Double covalent bond)

Covalent Compounds of ELEMENTS Nitrogen, N2 (Triple covalent bond)

Covalent Compounds of COMPOUNDS

Draw the ‘dot-and-cross’ diagram for each of the following covalent compounds.

1. Hydrogen chloride2. Ammonia

Covalent Compounds of COMPOUNDS Water, H2O

Covalent Compounds of COMPOUNDS Carbon dioxide, CO2

Simple Molecular Substances

Consists of small molecules, e.g. bromine

Simple Molecular Substances

Within the moleculeAtoms are held together by strong covalent bonds

Between moleculesWeak van der Waals’ forces (intermolecular forces)

Iodine, I2

Within each iodine molecule, the iodine atoms are held together by strong covalent bonds.

Between the iodine molecules, there are only weak van der Waals’ forces holding the molecules together.

Methane, CH4

In a molecule of methane, CH4, the four C–H covalent bonds are strong.

However, weak van der Waals’ forces between methane molecules hold them together loosely. Therefore, methane exists as a gas at room temperature and pressure.

Physical Properties

Physical state Most substances are liquids or gases at

room temperature. Forces between molecules are weak,

allowing molecules to move freely.

Low M.P. & B.P. Little energy required

to overcome the (weak) intermolecular forces

(Usually <200°C)

Melting & Boiling Points

Covalent substance Melting point (C) Boiling point (C)

Carbon dioxide -56 -79

Chlorine -101 -35

Hydrogen -259 -253

Methane -183 -161

Oxygen -214 -183

Water 0 100

Physical Properties

Volatility Low B.P. = Volatile Evaporate easily (to give a smell)

Electrical conductivity Do not conduct electricity. (Some exceptions, e.g. graphite) No free-moving ions or electrons to conduct electricity

Solubility Most molecular substances are insoluble in water, but

dissolve in organic solvents. (Some exceptions, e.g. alcohol and sugar, hydrogen chloride)

So, what have you learnt?

Covalent bonding The definition of a covalent bond

A covalent bond is a bond formed by the sharing of a pair of electrons.

Formed between atoms of non-metals (with exceptions!)

Atoms share electrons so that a octet structure can be obtained

Steps to take…

1. Ionic or covalent?2. Determine the electronic configuration of the

atoms involved3. How many electrons needed to achieve stable

electronic structure?4. Now, transfer/share the electrons!

So, what have you learnt?

Simple molecular structure Small covalent molecules Strong covalent bonds between the atoms in the

molecule Weak intermolecular forces 5 physical properties

Giant Covalent Structures

Graphite Diamond

Giant Covalent Structures

Diamond Each carbon atom is joined to four other carbon

atoms by strong covalent bonds. (Draw!)

Graphite Each carbon atom is joined to three other carbon

atoms by strong covalent bonds. (Draw!)