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Covalent bonding — KCSE Chemistry

KCSE Chemistry · 77 practice questions · 4 syllabus objectives · 4 revision lessons

29 easy30 medium18 hard

Last updated · Aligned to the KNEC KCSE syllabus

What You'll Learn

Key learning outcomes for this topic, aligned to the KNEC KCSE syllabus.

Describe covalent bond formation by sharing of electrons using dot-and-cross diagrams

Distinguish between single, double and triple covalent bonds with examples

Explain the properties of covalent compounds in terms of their molecular structure

Covalent bonding

Revision Notes

Concise lesson notes for Covalent bonding, written to the KCSE Chemistry marking standard. Read the first lesson free below.

Understanding Covalent Bond Formation

Covalent bonding occurs when two non-metal atoms share electrons to achieve a full outer shell, leading to stability. This sharing of electrons can be illustrated using dot-and-cross diagrams. In these diagrams, dots represent the electrons from one atom, while crosses represent the electrons from the other atom.

Key steps to draw a dot-and-cross diagram:

  1. Identify the two non-metals involved in the bond.
  2. Determine the number of valence electrons for each atom.
  3. Show the sharing of electrons by placing dots and crosses around the atoms.

For example, in a hydrogen molecule (H₂):

  • Each hydrogen atom has one valence electron.
  • The diagram shows one dot from one hydrogen and one cross from the other hydrogen sharing their electrons.

This results in a single covalent bond between the two hydrogen atoms, represented as H: H (where ':' indicates the shared pair of electrons).

Key points to remember

  • Covalent bonds form by sharing electrons between non-metals.
  • Dot-and-cross diagrams visually represent electron sharing.
  • Each shared pair of electrons constitutes one covalent bond.
  • Atoms achieve stable electron configurations through covalent bonding.

Worked example

Question: Draw a dot-and-cross diagram for a chlorine molecule (Cl₂). Answer: Each chlorine atom has 7 valence electrons. The diagram shows one atom with 7 dots and the other with 7 crosses, sharing one pair of electrons, represented as Cl:Cl.

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Lesson 2: Understanding Covalent Bonds

Objective: Distinguish between single, double and triple covalent bonds with examples

Covalent bonds are formed when two atoms share electrons. There are three types of covalent bonds: single, double, and triple.

  • Single covalent bond: This occurs when one pair of electrons is shared between two atoms. For example, in a hydrogen molecule (H₂), each hydrogen atom shares one electron, forming a single bond.

  • Double covalent bond: This occurs when two pairs of electrons are shared. A common example is the oxygen molecule (O₂), where each oxygen atom shares two electrons, resulting in a double bond.

  • Triple covalent bond: This occurs when three pairs of electrons are shared between two atoms. An example is the nitrogen molecule (N₂), where each nitrogen atom shares three electrons, forming a triple bond.

In summary, the number of shared electron pairs distinguishes these bonds: one pair for single, two pairs for double, and three pairs for triple bonds.

  • Single bond shares one pair of electrons.
  • Double bond shares two pairs of electrons.
  • Triple bond shares three pairs of electrons.
  • Examples include H₂, O₂, and N₂ respectively.
  • Bond strength increases with more shared pairs.

Distinguish between single, double, and triple covalent bonds with examples.

  • A single covalent bond (H₂) shares one pair of electrons.
  • A double covalent bond (O₂) shares two pairs of electrons.
  • A triple covalent bond (N₂) shares three pairs of electrons.
Lesson 3: Understanding Covalent Compounds Properties

Objective: Explain the properties of covalent compounds in terms of their molecular structure

Covalent compounds are formed when two or more non-metals share electrons. Their properties can be explained based on their molecular structure.

Key properties of covalent compounds include:

  • Low melting and boiling points: Most covalent compounds exist as gases or liquids at room temperature due to weak intermolecular forces.
  • Poor electrical conductivity: In solid form, covalent compounds do not conduct electricity as they lack free-moving charged particles.
  • Solubility in non-polar solvents: Many covalent compounds are soluble in non-polar solvents like benzene but insoluble in water.
  • Brittleness: When solid, covalent compounds tend to be brittle and break easily upon applying force.

These properties arise from the molecular structure, which is characterized by discrete molecules held together by covalent bonds. The strength of these bonds affects the compound's physical properties. For example, in diamond, the strong covalent bonds result in a high melting point, while in methane, the weak intermolecular forces lead to low melting and boiling points.

  • Covalent compounds have low melting and boiling points.
  • They do not conduct electricity in solid form.
  • Many are soluble in non-polar solvents.
  • Covalent compounds are often brittle in solid form.

Explain why water (H2O) has a higher boiling point than methane (CH4).

  • Water has strong hydrogen bonds due to polarity.
  • Methane has weak van der Waals forces, resulting in a lower boiling point.
Lesson 4: Understanding Covalent Bonding

Objective: Covalent bonding

Covalent bonding occurs when two atoms share pairs of electrons. This type of bond typically forms between non-metal atoms, allowing them to achieve a stable electron configuration. Here are key features of covalent bonds:

  • Electron Sharing: Atoms share one or more pairs of electrons.
  • Bond Strength: The strength of a covalent bond depends on the number of shared electron pairs; single, double, and triple bonds exist.
  • Molecular Formation: Covalent bonds lead to the formation of molecules, such as water (H₂O) and carbon dioxide (CO₂).
  • Polarity: The sharing of electrons may be equal (nonpolar) or unequal (polar), influencing the molecule's properties.

Understanding covalent bonds is essential for grasping more complex chemical interactions and reactions. For example, in a water molecule, each hydrogen atom shares one electron with the oxygen atom, resulting in a polar covalent bond due to the difference in electronegativity between oxygen and hydrogen.

  • Covalent bonds form by sharing electron pairs between atoms.
  • Typically occur between non-metal atoms.
  • Bond strength increases with more shared electron pairs.
  • Molecules can be polar or nonpolar based on electron sharing.
  • Examples include H₂O and CO₂.

Explain the formation of a water molecule (H₂O) using covalent bonding.

  • Water is formed by two hydrogen atoms sharing electrons with one oxygen atom.
  • Each hydrogen shares one electron, creating two polar covalent bonds.

Sample Questions

Read 3 questions and answers free. Sign up to access all 77 questions with full KNEC-style marking schemes and a personalised study plan.

1
easySHORT ANSWER4 marks

The study of molecular structures reveals fascinating variations in the properties of certain elements. In this context, consider the different forms that carbon can take, each exhibiting unique characteristics and applications. (a) Define the term allotropy. (b) Name two allotropes of carbon. (c) Match each of the following uses to the correct allotrope and the property it depends on: (i) making drill bits (ii) making lubricants for high-temperature machinery

Answer & marking scheme

Part (a) — 4 marks
Allotropy is the existence of an element in two or more different physical forms (allotropes) in the same physical state (1 mk)
2
easySHORT ANSWER3 marks

In the study of chemical structures, understanding the fundamental concepts related to molecular formation is essential. This includes defining key terms and exploring the characteristics of different molecules based on their atomic composition. (a) Define the term "molecule". (b) Define the term "atomicity" of a molecule. (c) State the atomicity of ozone (O₃).

Answer & marking scheme

Part (a) — 3 marks
A molecule is a group of two or more atoms held together by covalent bonds (1 mk)
3
easySHORT ANSWER4 marks

The study of molecular structures reveals fascinating variations in the properties of certain elements. In this context, consider the different forms that carbon can take, each exhibiting unique characteristics and applications. (a) Define the term allotropy. (b) Name two allotropes of carbon. (c) Match each of the following uses to the correct allotrope and the property it depends on: (i) making drill bits (ii) making electrodes

Answer & marking scheme

Part (a) — 4 marks
Allotropy is the existence of an element in two or more different physical forms (allotropes) in the same physical state (1 mk)
4

In the study of molecular interactions, understanding the nature of atomic connections is crucial. This involves exploring the different types of bonds formed when atoms share electrons, which significantly influence the properties and behaviors of various substances. (a) Define a covalent bond. (b) Distinguish between single, double and triple covalent bonds. (c) Give one example of a molecule that contains a triple bond.

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Frequently asked questions

What does the KCSE Chemistry topic "Covalent bonding" cover?

Covalent bonding covers Describe covalent bond formation by sharing of electrons using dot-and-cross diagrams; Distinguish between single, double and triple covalent bonds with examples; Explain the properties of covalent compounds in terms of their molecular structure, and more, all aligned to the official KNEC KCSE Chemistry syllabus.

How many practice questions are available for Covalent bonding?

HighMarks has 77 Covalent bonding practice questions for KCSE Chemistry, each with a full marking scheme. The first 3 are free; sign up to access the rest, plus all KCSE mock exams and past papers.

Are these aligned with the KNEC KCSE syllabus?

Yes. Every objective on this page is taken directly from the official KNEC KCSE Chemistry syllabus. Practice questions match the KCSE exam format and are graded against the standard KNEC marking scheme.

How should I revise Covalent bonding for the KCSE exam?

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