CHEMICAL BONDING. Overview Bonding IonicCovalentMetallic StructureGiant ionic Simple molecular Giant covalent Giant Metallic Example Sodium chloride WaterDiamondIron.

CHEMICAL BONDING

Overview

Bonding Ionic Covalent MetallicStructure Giant

ionicSimple

molecularGiant

covalentGiant

MetallicExample Sodium

chlorideWater Diamond Iron

Bonding and structure explains the properties of a substance!

Physical & Chemical Properties

‘property’: ‘what something is like’ Physical properties of a substance are those that

can be observed or measured without the substance changing into another substance.

Chemical properties of a substance describe the change of a substance into another substance.

Some examples of physical properties:Melting and

boiling pointsElectrical

conductivitySolubility in water (or other solvents)

Ionic Bond: The Definition

An ionic bond… is the force of attraction between

opppositely charged ions in a compound.

Giant Ionic StructuresPhysical Properties: M.P. & B.P.

Ionic compounds have high melting and boiling points.

strong electrostatic forces of attraction between the ions in an ionic compound

large amount of heat is needed to break the strong ionic bonds holding the ions together

Giant Ionic StructuresPhysical Properties: Electrical Conductivity

Ionic compounds do not conduct electricity in the solid state. It conducts electricity

in the molten and aqueous state.

Why do ionic compounds only conduct electricity in the molten or aqueous state, but not in the solid state?

ions can move in the molten or aqueous state moving ions carry the electric current

Giant Ionic Structures Physical Properties: Solubility

Ionic compounds are soluble in water but insoluble in organic solvents.

ions attract water molecules disrupts the crystal structure cause the ions to separate and go into solution

Giant Ionic StructuresPhysical Properties: Volatility

Ionic compounds are not volatile and hence, have no smell.

cannot evaporate easily because of strong ionic bonds holding the ions together

A volatile substance evaporates easily.

Giant Ionic StructuresPhysical Properties: Physical State

Ionic compounds are hard, crystalline solids. ions held in place by strong ionic bonds, make the

crystal hard ions are arranged in straight rows and form

structure with flat sides, resulting in a crystalline structure (flat sides & regular shapes)

Compare and Contrast

Ionic VS Covalent

Similarities 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

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 intermolecular forces (van der Waals’ 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 intermolecular 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)