Covalent Bonds

Covalent Bonds

• It is a chemical bond formed from the sharing of valence electrons between non-metal atoms to achieve the stable duplet of octet electron arrangement.
• Each shared pair of electrons is as one covalent bond.
• It produces molecules.
• Usually the covalent bonds form between non-metal atoms from Group 15, 16 and 17 and sometimes can be formed from Group 14 (carbon and silicon) and hydrogen.
• Covalent bond can be formed from atoms of the same element and atoms of different elements.

Example:

Non-metal	+	Non-metal	–>	Covalent compound
Bromine	+	bromine	–>	Bromine (Br2)
Nitrogen	+	nitrogen	–>	Nitrogen (N2)
Carbon	+	chlorine	–>	Tetrachloromethane (CCl4)
Hydrogen	+	oxygen	–>	Water (H2O)
Hydrogen	+	nitrogen	–>	Ammonia (NH3)

Types of covalent bond formed:

• Single bond = one pair of electrons shared between two atoms.
• Double bond = two pair of electrons shared between two atoms.
• Triple bond = three pair of electrons shared between two atoms.

Non-metal
Group 15

• A nitrogen atom with an electron arrangement of 2.5 needs three more electrons to achieve stable octet electron arrangement after it contribute (through sharing) three valence electrons to another atom (can be from Group 14, 15, 16, 17).
• A phosphorus atom with an electron arrangement of 2.8.5 need three more electrons to achieve stable octet electron arrangement after it contribute (through sharing) three valence electrons to another atom (can be from Group 14, 15, 16, 17).

Group 16

• An oxygen atom with an electron arrangement of 2.6 needs two more electrons to achieve stable octet electron arrangement after it contribute (through sharing) two valence electrons to another atom (can be from Group 14, 15, 16, 17).
• A sulphur atom with an electron arrangement of 2.8.6 need two more electrons to achieve stable octet electron arrangement after it contribute (through sharing) two valence electrons to another atom (can be from Group 14, 15, 16, 17).

Group 17

• A fluorine atom with an electron arrangement of 2.7 needs one more electron to achieve stable octet electron arrangement after it contribute (through sharing) one valence electron to another atom (can be from Group 14, 15, 16, 17).
• A chlorine atom with an electron arrangement of 2.8.7 need one more electron to achieve stable octet electron arrangement after it contribute (through sharing) one valence electron to another atom (can be from Group 14, 15, 16, 17).

Predict the Formula of a Covalent Compound

• Non-metal X atom (valence electron is a)
• Combine with another non-metal Y atom (valence electron is b)
• b = simplest ratio (n) and a = simplest ratio (m)
• Formula of a covalent compound formed, X_nY_m

 Some common covalent compound

• Hydrogen molecule, H₂ (single bond)
• Chlorine molecule, Cl₂ (single bond)
• Bromine molecule, Br₂ (single bond)
• Fluorine molecule, F₂ (single bond)
• Water molecule, H₂O (single bond)
• Nitrogen trifluoride molecule, NF₃ (single bond)
• Tetrachoromethane / carbon tetrachloride, CCl₄ (single bond)
• Ammonia molecule, NH₃ (single bond)
• Oxygen molecule, O₂ (double bond)
• Carbon dioxide molecule, CO₂ (double bond)
• Nitrogen molecule, N₂ (triple bond)
• Ethyne molecule, C₂H₂ (triple bond)

Structure of covalent compounds

• Can be simple molecular structure or giant molecular structure.
• The atoms in the molecule are joined together by strong covalent bond but intermolecular forces are weak by weak van der Waals’ forces.