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Chapter 5: Chemical Bonds

1. Chemical Bonds - Compounds are formed through the

formation of chemical bonds among atoms. - Noble gases are very stable as they have

achieved the stable duplet or octet electron arrangements.

- Atoms of other elements tend to achieve the stable electron arrangement by the transfer of electron or sharing of electron.

- There are two types of chemical bonds:

ionic bonds and covalent bonds. - Only valence electrons are involved in

bonding, electrons in filled shells do not take part in bonding.

2. Ionic Bonds - Ionic bonds are usually formed through the

transfer of electron between atoms of metal and non-metal.

- Metal atoms donate electrons whereas non-metal atoms accept electrons to achieve the stable electron arrangement.

- Metal usually form positive ions. - Positive ions or cations are formed when

neutral atoms donate electrons.

- In positive ions, the number of electrons is

less than the number of proton. - Non-metal usually form negative ions. - Negative ions or anions are formed when

neutral atoms accept electrons. - In negative ions, the number of electron is

more than the number of proton.

3. Ionic compound - Ionic compound are compounds that are

formed through ionic bonds. - Example: NaCl - Na (2.8.1) Na+ (2.8) / Cl (2.8.7) Cl-

(2.8.8) - Na+ and Cl- are attracted to one another to

form a solid sodium chloride, NaCl compound.

- This is due to the existence of a strong

electrostatic force between the oppositely-charged ions.

- The attractive force between the ions is called an ionic bond or electrovalent bond.

4. Covalent bonds - Covalent bonds are formed when non-metal

atoms share electrons to achieve stable electron arrangements.

- Lewis structure is used to show the valence electrons of the atoms involved in the formation of a covalent bond.

- Types of covalent bonds include

- Single bond: A pair of electron is shared

between two atoms. Example H-H - Double bonds: Two pairs of electrons are

shared between two atoms. C=C - Triple bonds: Three pairs of electrons are

shared between two atoms. NN

Ionic Compounds Covalent Compounds Exists as solids at room temperature May exists as solids, liquids or

gases

5. Properties of Ionic

and Covalent Have high melting and boiling points Have low melting and boiling

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points Conduct electricity in aqueous solution or molten state

Do not conduct electricity

Usually dissolve in water Usually do not dissolve in water

Compound

Usually do not dissolve in organic solvents Usually dissolve in organic solvents

Example Cations: 1. Na Na+ + e- 2. Mg Mg2+ + 2e-

Na

Na+

2.8 Na2.8.1

+

Na

Mg

Mg2+

2.8 Mg2.8.2

2+

Mg

.

3. Al

Al

Al2.8.3

Anions: 1. Cl + e- Cl- 2. O + 2e- O2-

Cl Cl

-

Cl2.8.7

Cl2.8.8

+ 1e-

+ 2e-

O2.8

O2.6

2-

OO

3. N

N2.5

+ 3e-

N2.8

3-

NN

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Ionic Compound: Metal + Non-metal Ionic Compound Transfer of electron from metal to non metal Example 1: Sodium Chloride, NaCl

Example 2: Magnesium Chloride, MgCl2

Example 3: Aluminium Chloride Example 4: Aluminium Oxide

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Covalent Compound: Non-metal + Non-metal Covalent Compound Sharing electron between the two non-metal Example 1: Chlorine gas, Cl2

Example 2: Oxygen gas, O2

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Example 3: Nitrogen gas, N2

Example 5: Water, H2O Example 7: Ammonia, NH3

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Example 4: Carbon dioxide, CO2

Example 6: Hydrochloride, HCl Example 8: Methane, CH4

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Properties of Ionic Compounds

1. Ionic compounds are exists as solids at room temperature.

2. Ionic compounds have high melting point and boiling points because the ions in ionic

compounds are held together by strong ionic bonds. A lot of energy is used to overcome the

strong electrostatic forces that are holding the ions together.

3. Ionic compound do not conduct electricity in solid state. Ions in solid ionic compounds are fixed

in positions in the crystal lattice structure and do not move freely. In aqueous solution or molten

state, ions are free to move and ionic compounds can conduct electricity.

4. Ionic compound are not volatile. They do not change to vapour when heated.

5. Most ionic compounds are soluble in water.

6. Most ionic compounds are insoluble in organic solvents.

1. Exist as solids at room temperature.

3. Conduct electricity in aqueous solution or molten state.

4. Non-volatile

5. Usually dissolve in water.

6. Usually do not dissolve in organic solvents

2. Have high melting and boiling points.

Ionic

Compounds

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Properties of Covalent Compounds

1. Covalent compounds are exists as solids, liquids or gases.

2. Ionic compounds have low melting point and boiling points because their molecules are held

together by weak intermolecular forces. Less heat energy is required to overcome these forces.

3. Covalent compound do not conduct electricity in all state. A covalent compound consists of

neutral molecules.

4. Covalent compounds are volatile. They can change to vapour when heated.

5. Most covalent compounds are insoluble in water. They cannot form bonds with water.

6. Most covalent compounds can dissolve in organic solvents. They have the same type of

intermolecular forces as the covalent solvents.

1. May exist as solids, liquids or gases.

3. Do not conduct electricity.

4. Volatile

5. Usually do not dissolve in water.

6. Usually dissolve in organic solvents

2. Have low melting and boiling points.

Covalent

Compounds