Chapter 6: Chemical Bonding

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Learning outcomes At the end of the lesson, students should be able to

understand and explain:

Ionic bonding.

Covalent bonding.

Octet rule.

Lewis structure

Bond polarity and bond strength.

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Octet rule Almost all elements in its natural state are not stable.

Only elements of group 8 are stable.

The stability of group 8 elements are due to the fact that its valence shell are full.

This is known as the octet rule.

Elements that do not have fully filled valence shells will try to achieve octet stability by either: Donating electron

Accepting electron

Sharing electron 3

Ionic bond Ionic bonds are usually formed between metals and non

metals.

Metals: Tend to donate its valence electrons

Forms positive ion or cation

Non-metals: Tend to accept electrons

Forms negative ion or anion

Ionic bond is the strong electrostatic forces of attraction between two oppositely charged ions. 4

Covalent bond Covalent bonds are usually formed between non-metals

In order to achieve octet configuration, non-metals tend to share its valence electrons.

Covalent bond is formed when non-metals valence shell overlaps to allow sharing of electrons.

Rules of covalent bond: The sharing of electron between atoms are mutual (if atom A

shares one electron, atom B will also share one electron)

An atom will share exactly the same amount of electrons it needs to achieve octet configuration (chlorine has 7 valence electrons, it needs 1 e to achieve octet stability, hence it will share only 1 e)

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Lewis structure Lewis structure only shows the valence electrons of atoms

that are involved in covalent bonding.

Dots and crosses are still used to represent different electrons.

Lewis structure is simplified as it removes the need to draw the other inner shells.

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Lewis structure

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Electronegativity Electronegativity is the ability of an atom to attract electrons

in a covalent bond

Different atoms have different value of electronegativity

The stronger the electronegativity, the greater the ability to attract electrons

General pattern:

Non-metals have greater electronegativity compared to metals

Electronegativity increases across the period

Electronegativity decreases down the group

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Bond polarity When two of the same atoms forms a covalent bond, the electrons

are shared equally resulting in a non-polar bond

When two different elements are bonded, the electrons are not shared equally

The more electronegative atom will pull the electrons closer towards itself

The electrons are unsymmetrically distributed

The difference in electronegativity of atoms in a covalent bond results in polar bonds

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Bond Polarity

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Bond Polarity The unequal distribution of electrons results in polar bonds

The bond has a dipole indicated by

+ (less electronegative atoms)

(more electronegative atoms)

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Bond strength Bond strength refers to the strength of a particular covalent

bond.

Bond strength can be measured based on bond energy.

Bond energy can be defined as the energy needed to break one mole of a particular covalent bond.

Bond energies varies from compound to compound.

One of the factors that affect bond energy is the length of the bond.

The shorter the bond, the higher the bond energy. 12

Bond strength

Bond Bond length (nm) Bond energy (kJ mol-1)

H-H 0.074 435

Cl-Cl 0.198 243

O=O 0.121 495

NN 0.110 941

H-Cl 0.109 414

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THE END

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