Chapter 5 Chemical Bonds

Chapter 5

Chemical Bonds

Formation of Chemical Bonds

• Types of chemical bonds:

1. Ionic bond: formed when atom joined together by transferring of electrons between metal and non-metal atom

2. Covalent bond: formed when atom joined together by sharing electron between non-metal and non-metal atom

Ionic Bonds

• Formed when atom joined together by transferring of electrons between metal and non-metal atom

Metal atom Non-metal atom e

donate electron receive electron

Achieve the stable electron arrangement

Formation of ions

Neutral atom

Cation (+)

Anion (-)

Donate electrons Accepts electrons

Aluminium, Al

2.8.3

Al

Donate 3 electrons

Al

3+

2.8

Aluminium atom, Al Aluminium ion, Al 3+

Al → Al + 3e 3+ -

Oxygen, O

2.6

O

Accepts 2 electrons

O

2-

2.8

Oxygen atom, O Oxide ion, O 2-

O + 2e → O 2- -

Formation of ionic bonds

• Ionic compounds

Compounds that are formed through ionic bonds

Lets investigate the formation of

sodium chloride, NaCl

2.8.1

Na Cl +

2.8.7

2.8 2.8.8

Cl

-

Na

+

Explain the formation of sodium chloride

+

-

- +

+

-

1. Sodium atom, Na with the electron arrangement 2.8.1

2. Chlorine atom, Cl with the electron arrangement 2.8.7

3. Sodium atom, Na will donate 1 electron to achieve the stable electron arrangement to form sodium ion, Na

Na → Na + e

4. Chlorine atom, Cl will receive 1 electron to achieve the stable electron arrangement to form chloride ion, Cl

Cl + e → Cl

5. One sodium ion, Na and one chloride ion, Cl attracted by strong electrostatic force to form sodium chloride, NaCl

F + e → F

5. One magnesium ion, Mg and two fluoride ion, F attracted by strong electrostatic force to form magnesium fluoride, MgF

4. Fluorine atom, F will receive 1 electron to achieve the stable electron arrangement to form fluoride ion, F

Mg → Mg + 2e

3. Magnesium atom, Mg will donate 2 electron to achieve the stable electron arrangement to form magnesium ion, Mg

Explain the formation of magnesium fluoride

2+

-

- 2+

2+

-

1. Magnesium atom, Mg with the electron arrangement 2.8.2

2. Fluorine atom, F with the electron arrangement 2.7

2

2.8.2

Mg

F

+

2.7

2.7

F

2.8 2.8

F

-

Mg

2+

2.8

F

-

Exercise

• Explain the formation of ionic bond of:

1. Lithium fluoride

2. Sodium oxide

3. Magnesium oxide

4. Boron oxide

5. Aluminium oxide

Covalent Bonds

• Formed when atom joined together by sharing electron between non-metal and non-metal atom

• Types of covalent bonds:

1. single covalent bonds

2. double covalent bonds

3. triple covalent bonds

Single covalent bonds

• A covalent bond formed when a pair of electrons is shared between two atoms

Lets investigate the formation of hydrogen molecule

H

1

H +

1

H H

2 2

5. A single covalent compound with formula H is formed

4. Two hydrogen atom share pairs of electron to achieve the stable electron arrangement

3. Hydrogen atom, H contribute one electron each for sharing

Explain the formation of hydrogen molecule

-

1. Hydrogen atom, H with the electron arrangement 1

2. Hydrogen atom, H has one valence electron

2

Double covalent bonds

• A covalent bond formed when a 2 pair of electrons is shared between two atoms

Lets investigate the formation of oxygen molecule

2.6

+

2.6

2.8 2.8

O O

O O

5. A double covalent compound with formula O is formed

4. Two oxygen atom share 2 pairs of electron to achieve the stable electron arrangement

3. Oxygen atom, O will contribute 2 electron each for sharing

Explain the formation of oxygen molecule

-

1. Oxygen atom, O with the electron arrangement 2.6

2. Oxygen atom, O has 6 valence electron

2

Triple covalent bonds

• A covalent bond formed when a 3 pair of electrons is shared between two atoms

Lets investigate the formation of nitrogen molecule

2.5

+

2.5

2.8 2.8

N N

N N

5. A triple covalent compound with formula N is formed

4. Two nitrogen atom share 3 pairs of electron to achieve the stable electron arrangement

3. Nitrogen atom, N will contribute 3 electron each for sharing

Explain the formation of nitrogen molecule

-

1. Nitrogen atom, N with the electron arrangement 2.5

2. Nitrogen atom, N has 5 valence electron

2

7. A covalent compound with formula H O is formed

6. Two hidrogen atom share 1 pairs of electron with 1 oxygen atom to achieve the stable electron arrangement

5. Oxygen atom, O contribute 2 electron for sharing

Explain the formation of water molecule

1. Hydrogen atom, H with the electron arrangement 1

4. Hidrogen atom, H contribute 1 electron for sharing

2

2. Oxygen atom, O with the electron arrangement 2.6

3. The valence electron of hydrogen atom, H is 1 and oxygen atom, O is 6

O H H

Explain the formation of:

-

1. Carbon dioxide molecule

4 2. Methane, CH

Properties of Ionic and Covalent Compounds

Ionic Compound

Exist as solid at room temperature

High melting and boiling points

Conduct electricity in aqueous solution or molten state

Dissolve in water BUT do not dissolve in organic solvents

Covalent Compound

Exist as solid, liquids or gases

Low melting and boiling points

Do not conduct electricity at any state

Dissolve in organic solvents BUT do not dissolve in water

Electrical conductivity

• In solid state, ions do not move freely. Hence, ionic compound does not conduct electricity in solid state

• In aqueous or molten state, ions are free to move. Hence, the compound can conduct electricity

Electrical conductivity

• A covalent compound consist of neutral molecules

• There are no free moving ions in covalent compound

• Hence, covalent compounds do not conduct electricity at any state

Melting and boiling points

• Ionic compounds are held together by strong electrostatic forces

• More heat energy is needed to overcome the strong forces

Melting and boiling points

• Covalent compounds are held together by weak intermolecular forces

• Less heat energy is needed to overcome the weak forces