Sn 1 Chemical Bonding

7/28/2019 Sn 1 Chemical Bonding

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Chemical bonding

The force of attraction that binds atoms together in a chemical substance is called the

chemical bond.

Chemical bond can be divided into five main types, namely,

a) Ionic bond

b) Covalent bond

c) Metallic bond

A. Ionic (electrovalent) bond

Ionic bond is formed by the transfer of one or more electrons from the outer orbital of

one atom to the outer orbital of another atom.

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

The formation of an ionic compound involves a metal with low ionization energy and

a non-metal with high electron affinity.

A metal atom and a non-metal atom are involved.

The metal atom loses electron/electrons, and a non-metal atom accepts the

electron/electrons.

A positively charged ion or cation is formed from a metal atom.

A negatively charged ion or anion is formed from a non-metal atom due to the

acceptance of electrons from metal atoms.

Example

Lithium fluoridea) By using electronic configuration

Li (1s22s1) + F (1s22s22p5) Li+ (1s2) + F- (1s22s22p6)

b) By using orbital diagrams


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Calcium chloride

c) By using dot-and-cross diagrams

Strength of ionic bond

1) Ionic bond is the result of strong electrostatic force of attraction between

positive and negative ions. Hence, the strength of an ionic bond is

a) Proportional to the charge on the ions

b) Inversely proportional to the distance between the ions.

2) The higher the charge on the ions and/or the smaller the ionic radius, the

stronger is the attractive force between the ions. Hence, the stronger the

ionic bond.

Polyatomic ions

1. Polyatomic ions are ions that contain more than one atoms.

2. Metals also form ionic compounds with polyatomic ions, for example, Na2CO3,

MgSO4 and KHCO3.

b. Covalent bond


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Covalent bond is the electrostatic attraction between the pair of shared electrons and

the two positively charged nuclei of the atoms.

It is usually formed by overlapping of the atomic orbital of one atom with that of

another atom. The covalent bond is usually formed between elements of non-metals.

The strength of a covalent bond is proportional to the area where atomic orbitals

overlap.

Example

1. Hydrogen

Atom Dot-and-cross

diagram

Bond diagram Formula

H H H H-H H2

2. Bromine molecule

*Bond pair : A pair of electron in a covalent bond.

*Lone pair: Electron- pair that are not involved in bonding.

Octet Rule

Atoms will lose, gain or share electrons to achieve the electron configuration of the nearest

noble gas (8 valence electrons except for He with 2).

Molecules that Octet Rule Molecule that do not obey Octet Rule

CH4

Cl2

HF

NH3

BeCl2

BCl3

PCl5

SF6

Multiple covalent bond


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Double bond Triple bond

Ethene (C2H4) Ethyne (C2H2)

Coordinate bond (Dative covalent bond)

Coordinate bond is a covalent bond formed when one atom donates a lone pair of electrons

to another atom that has a vacant valence orbital.

Example

Ammonium Ion

A dative bond is represented by an arrow pointing from the electron-pair donor (nitrogen

atom) to the electron-pair acceptor (hydrogen atom).

Valence-Shell Electron-Pair Repulsion (VSEPR) Theory

VSEPR state that:

a) The electron-pair around the central atom repel each other

b) The electron-pair (bonding pair and lone pair) arrange themselves to be as far

apart as possible to minimize the force of repulsion

c) The force of repulsion decrease in the order:

c. Metallic Bonding

Metallic bond is the electrostatic attraction between positive metal ions and

the sea of delocalised electron.

Metal have high electric and thermal conductivity because of the presence of

delocalised electron.

Band theory


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The band theory suggests that where there are 2 groups of energy level:

1) Valence band (lower) : completely filled with electron.

2) Conduction band (higher) : contain electron that free to move.

Conductor Insulator Semi-conductor

Example Mg, Al, Fe P, S, diamond Si

Diagram

Explanation In solid conductor,

the valence band is

fully filled while the

conduction band is

partially filled.

There is no energy

gap between the two

bands.

In the presence of a

potential difference,

electrons from the

valence band can

migrate into the

conduction band and

thus can conduct

electricity.

In insulator, the

valence band is fully

filled, while the

conduction band is

empty.

There is a large gap

between the two

bands.

The electrons in the

valence band cannot

move into the

conduction band due

to the large energy

gap between the two

bands.

In semi-conductor, the

valence band is fully

filled, while the

conduction band is

empty.

The two bands are

separated by a small

energy gap.

The conductivity is

lower than that of

conductors because

the number of electrons

in the conduction band

of semi-conductor are

fewer.

At room temperature,

some electron in the

valence band might

have enough energy to

be promoted to the

conduction band and

thus conduct electricity.


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Sn 1 Chemical Bonding