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Atoms, Elements and Compounds - Covalent bonding

Grade 12IGCSEChemistry

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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A covalent bond is formed when two non-metal atoms share one or more pairs of electrons to achieve a stable outer shell electron configuration, typically resembling a noble gas (the octet rule).

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The bond is the result of the electrostatic attraction between the shared pair of electrons and the positive nuclei of the bonded atoms.

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Covalent substances can exist as simple molecules (e.g., H2H_2, O2O_2, H2OH_2O, CH4CH_4) or giant covalent structures (e.g., Diamond, Graphite, SiO2SiO_2).

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Simple molecular substances have low melting and boiling points because, although the covalent bonds within the molecules are strong, the intermolecular forces (Van der Waals forces) between molecules are weak.

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Giant covalent structures, also known as macromolecules, have very high melting points because a large amount of energy is required to break the many strong covalent bonds throughout the entire lattice.

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Multiple bonds occur when atoms share more than one pair of electrons: double bonds involve four shared electrons (e.g., O=OO=O in O2O_2), and triple bonds involve six shared electrons (e.g., N≡NN \equiv N in N2N_2).

📐Formulae

Total Valence Electrons=∑(Electrons in outer shells of all atoms)Total\ Valence\ Electrons = \sum (Electrons\ in\ outer\ shells\ of\ all\ atoms) pieces

H−H (Single bond representation)H-H \text{ (Single bond representation)}

O=C=O (Double bond representation in CO2)O=C=O \text{ (Double bond representation in } CO_2)

SiO2 (Empirical formula for the giant covalent structure of Silicon(IV) oxide)SiO_2 \text{ (Empirical formula for the giant covalent structure of Silicon(IV) oxide)}

💡Examples

Problem 1:

Describe the bonding and structure in Methane (CH4CH_4).

Solution:

Methane consists of one Carbon atom covalently bonded to four Hydrogen atoms.

Explanation:

Carbon has 44 valence electrons and needs 44 more to complete its octet. Each Hydrogen has 11 electron and needs 11 more. By sharing electrons, Carbon forms four single covalent bonds (C−HC-H). This forms a simple molecular structure with a tetrahedral shape.

Problem 2:

Explain why Graphite can conduct electricity while Diamond cannot, even though both are made of Carbon atoms.

Solution:

In Graphite, each Carbon atom is bonded to three others, leaving one delocalized electron per atom. In Diamond, each Carbon is bonded to four others.

Explanation:

In Diamond, all valence electrons are involved in localized covalent bonds, so there are no free charge carriers. In Graphite, the fourth valence electron of each Carbon atom becomes delocalized between layers, allowing it to flow and carry an electric current.

Problem 3:

Draw the dot-and-cross diagram for Nitrogen gas (N2N_2).

Solution:

:N≡N::N \equiv N:

Explanation:

Each Nitrogen atom has 55 valence electrons and requires 33 more to reach a full shell of 88. Therefore, two Nitrogen atoms share three pairs of electrons, forming a triple covalent bond. Each atom retains one lone pair of electrons.

Covalent bonding - Revision Notes & Key Formulas | IGCSE Grade 12 Chemistry