Chemical Bonding

Types of Bonds

• There are two kinds of Chemical bonds• Ionic and covalent• An ionic bond is formed when electrons are

transferred from one atom to the other e.g. NaCl • A covalent bond is formed when electrons are

shared between atoms e.g. H20

Octet Rule

• The noble gases are very unreactive.• They form practically no compounds.• Why?• They have 8 electrons in their outer shell-

unreactive• Rule: when bonding occurs, atoms tend to reach

an electron arrangement with 8 electrons in their outer shell

This fills the outershell and tends to givethe atom the stabilityof the inert gasses.

The Octet Rule

Atoms tend to gain, lose, or share electrons until they have eight electrons.

8

Ionic bonding

• An ion is a charged atom or group of atoms• An ionic bond is the force of attraction between

positively charged ions in a compound e.g. NaCl• Na+=Sodium ion = loses an electron• Cl¯ = Chlorine ion = gains an electron

Na = 2,8,1 Na+ = 2,8Cl = 2,8,7 Cl¯ = 2,8,8

Loses one electron

Gains one electron

NaCl

e¯

N=2

N=1

e¯

N=2

N=1

e¯

N=2

N=1

e¯

N=2

N=1

Na 2,8,1 Cl 2,8,7

Na+ 2,8, Cl¯ 2,8,8

N=3 N=3

N=3

Na

Na+

Cl

Cl¯

MgO

e¯

N=2

N=1

N=3

e¯

N=2

N=1

N=3

Mg= 2,8,2 O= 2,8,6

e¯

N=2

N=1

N=3

Mg2+= 2,8,

e¯

N=2

N=1

N=3

O2¯= 2,8,8

O

O2¯

Mg

Mg2+

e¯

e¯

e¯

e¯

Properties of Ionic Compounds

• Ionic compounds are usually solid at room temperature

• Usually have high melting and boiling points• Usually dissolve in water• Usually conduct electricity when molten and

when dissolved in water

Molecule

• A molecule is a group of atoms joined together

• e.g. H2

• H20 is a molecule consisting of two hydrogen atoms and one oxygen atom

Covalent Bonding

• Covalent bonds are formed as a result of the sharing of one or more pairs of bonding electrons.

• Each atom donates half of the electrons to be shared e.g. H2

H atom

H atom

H2molecule

Shared electrons

Hydrogen molecule

HH

H H

The oxygen molecule

Oxygen 2,6

e¯

Oxygen 2,6

e¯

e¯

e¯

e¯

Double bond

N=2

N=1

N=2

N=1

N=2N=2

N=1 N=1

O OOxygen O2

O O

O O

Oxygen 2,6 Two hydrogen atoms

Water H20

e¯e¯ e¯

e¯

e¯e¯

The water molecule

N=2

N=1

N=2 N=1

O

H

H

O

HH

OH

H

Covalent bond

Carbon 2,4 4 Hydrogen atoms

Methane gas CH4

Methane

N=2

N=1

N=2

N=1

H

HH

H

C

H H

H H

H

H

H

H C

Covalent bond

Properties of Covalent Compounds

• Covalent compounds are usually either a liquid or gas at room temperature

• Usually have low melting and boiling points• Many (but not all) do not dissolve in water• Covalent compounds do not conduct electricity

Covalent Bonding

-

-

-

-

n = 1

O

n = 2

+

-

----

-

-

O2

Sharing of electrons to achieve a stable octet (8 electrons in outer shell).

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

O

Formation of Cation

11p+

sodium atomNa

e-

loss of one outer electron

e-

e-

e-

e-e-

e-

e-

e- e-

e-

sodium ionNa+

11p+e-

e-

e-

e-e-

e-

e-

e-

e-

e-

e-

Formation of Anion

17p+

chlorine atomCl

e-

e-

e-

e-

e-e-

e-

e-

e- e-

e-

e-

e-

e-

e-

e-

e-

e-

gain of one outer electron

chloride ionCl1-

17p+e-

e-

e-

e-e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

Formation of Ionic Bond

chloride ionCl1-

sodium ionNa+

11p+e-

e-

e-

e-e-

e-

e-

e-

e-

e-

17p+e-

e-

e-

e-e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

Ionic Bonding

-

-

-

-

-

- -

-

-

-

-

- -

-

- -

n = 2

Na[Ne]3s1

n = 3

n = 3

+

-

-

-

-

-

- -

--

-

- -

-

- -

-

Cl[Ne]3s23p5

Na+

[Ne]Cl-

[Ne]3s23p6

NaCl

Transfer of electrons to achieve a stable octet (8 electrons in outside shell).

To investigate the ability of ionic and covalent substances to conduct electricity

• Apparatus required: power supply or battery, bulb, leads, crocodile clips, carbon electrodes

• Chemicals required: water, copper sulphate solution, methylated spirits, sodium chloride solution, table sugar solution, paraffin oil

Method

• Set up apparatus as shown• Insert the carbon electrodes into a solution of

copper sulphate• Write down what you observe• Repeat the experiment with various other

solutions. Using a wash bottle, wash the carbon electrodes before putting them into the next solution

Results

Summarise the results as follows:

Name of substance

Conduct electricity (Yes/No)

Copper sulphate

Methylated spirits

Sodium chloride

Paraffin oil

Table sugar