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Chapter 4: Chemical Bonding

Objectives:

1) Write the Lewis dot symbol for atom

2) State the octet rule3) Describe how atoms attain the octet (noble gas)

configuration

4) Define and describe the formation of ionic bond

5) Draw Lewis structures for simple ionic compound

6) List the properties of ionic compound

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Getting Started

When atoms interact to form a chemical bond (ionic or

covalent bond), only their outer regions are in contact.

only valence electrons involve in chemical

bonding.

Chemical bonds are the attraction forces that hold

the atoms together tightly in a molecule or to position

the ions in a lattice crystal of ionic compound.

Generally, the chemical and physical properties of acompound are governed by the types of chemical

bonding in the compound.

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Lewis structure (Lewis symbol) consists of the symbol of

an element and one dot or cross for each valence electronin an atom of the element.

The number ofunpaired dots indicates the number of

electrons a metal atom loses, the number a non-metal atom

gains or the number of covalent bonds a non-metal atomusually forms

Lewis Symbol

Symbole. conf. Lewis str.no. v.e.

Boron

sodium

fluorine

1s2

1s2 2s22p6

1s2 2s22p6

2s22p1

3s1

3s23p5

B

Na

F

3

1

7

B

Na

F

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Place one dot at a time on the four sides (top, right,

bottom, left) of the element symbol. Then, pair up the

dots until all are used.

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Octet Rule

In forming chemical bonds, atoms(representative elements excluding H, He, Li,

Be, B) tend to accept or donate or share a

number of electrons to acquire the electronicconfigurations of noble gases with 8 electrons

in the valence shell: ns2 np6

Maximum stability results when an atom isisoelectronic with a noble gas.

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Noble Gas Configuration

Non-metal

F

2s2 2p5

2s2 2p6

FAccept

electronFluoride ion

F Fshareelectron

2s2 2p6

Fluorinemolecule

Ne

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Stability of Metal Ions

Metals (representative elements)

K

[Ar] 4s1

K+

[Ar]

[Ne] 3s2 3p1

Al3+

[Ne]

Al

Noble gas

configuration

Sn2+

[Kr] 4d10 5s2[Kr] 4d10 5s25p2

Sn Inert pair effect

Donate

electrons

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Inert pair effect

In large atoms such as tin and lead the outer

s electrons are much more strongly held

compared to p electrons. As a result

p electrons are easily lost compared to s

electrons and therefore maintain its

stability.

Sn

[Kr] 4d10 5s25p2 [Kr] 4d10 5s2

Sn 2+

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Metals (transition elements)

Zn2+

1s22s2 2p6 3s2 3p6 3d10 4s2 1s22s2 2p6 3s2 3p6 3d10(pseudo-noble gas

configuration)

Zn

1s22s2 2p6 3s2 3p6 3d64s2Fe3+Fe

1s22s2 2p6 3s2 3p6 3d5

(half-filled orbital)

Stability of Metal Ions

Donateelectrons

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Ionic / Electrovalent Bond

Definition:The electrostatic forces of attraction between the

positively charged ions and the negatively charged

ions give rise to ionic or electrovalent bond.

metal

non-metal + ne

Low IE

HighAE

Cation + ne

anion

Ionic bond

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Formation of Ionic Bond

Na Cl

Elements with low

ionisation energydonate valence

electrons

[Ne] 3s1

Elements, with high

electron affinity,accept electrons

Example:

[Ne] 3s23p5[Ne] [Ne] 3s23p6

Na ClNa Cl

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Lewis Structure

for Ionic Compound

Li2O 2Li O2

CaF2 Ca F2 2

Al2O3 Al3 32 O 2

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Strength of Ionic Bonding

The product of charges on cation and anion

Ionic size (the distance between two ionic nuclei

Polarisation effect and the covalent character in

ionic bond (not discussed)

Electrostatic

energy

cation charge x anion charge

cation radius + anion radius

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Example :

NaCl and NaBr

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Properties of Ionic Compound

Hard and brittle

Meting and boiling point: very high

Solubility:soluble in polar solvent;

insoluble in non-polar solvent

Electrical conductivity:

a good conductor --- molten or aqueous only

explanation

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Place one dot at a time on the four sides (top, right,

bottom, left) of the element symbol. Then, pair up the

dots until all are used.