AQA GCSE FOUNDATION Chemistry: Covalent Bonding and Molecular Structures

AQA GCSE Foundation Chemistry: Covalent Bonding and Molecular Structures

What is covalent bonding?

Covalent bonding is a type of chemical bond that occurs when two atoms share electrons to achieve a full outer shell. This sharing of electrons creates a strong attraction between the atoms, holding them together.

How does covalent bonding work?

• Non-metals: Covalent bonds typically form between non-metals. Non-metals have a high electronegativity, meaning they strongly attract electrons.
• Sharing electrons: To achieve a stable electron configuration, non-metals share their valence electrons. This sharing allows both atoms to have a full outer shell, resembling the stable electron configuration of noble gases.

Simple Covalent Molecules:

Let's explore some examples of simple covalent molecules and their properties:

• Water (H?O):
  • Each hydrogen atom shares one electron with the oxygen atom, forming two covalent bonds.
  • Oxygen has six electrons in its outer shell and needs two more to fill it.
  • The molecule is bent or V-shaped due to the lone pairs of electrons on the oxygen atom.
  • Water is a good solvent, a liquid at room temperature, and has a high boiling point due to hydrogen bonding.
• Methane (CH?):
  • Each hydrogen atom shares one electron with the carbon atom, forming four covalent bonds.
  • Carbon has four electrons in its outer shell and needs four more to fill it.
  • Methane is a tetrahedral molecule, meaning it has a three-dimensional shape like a pyramid.
  • Methane is a gas at room temperature and is a major component of natural gas.
• Carbon dioxide (CO?):
  • Each oxygen atom shares two electrons with the carbon atom, forming two double covalent bonds.
  • Carbon has four electrons in its outer shell and needs four more to fill it.
  • The molecule is linear, with the carbon atom in the center.
  • Carbon dioxide is a gas at room temperature and is a greenhouse gas.

Properties of Covalent Compounds:

• Low melting and boiling points: Covalent compounds typically have low melting and boiling points because the forces between molecules are weak.
• Poor conductors of electricity: Covalent compounds do not conduct electricity because they do not contain free-moving electrons.
• Many are gases or liquids at room temperature: Due to weak intermolecular forces, many covalent compounds are gases or liquids at room temperature.
• Can be soluble in organic solvents: Covalent compounds are often soluble in organic solvents, such as ethanol and hexane.

Key Points to Remember:

• Covalent bonding involves sharing electrons between atoms.
• Covalent bonds typically form between non-metal atoms.
• The number of covalent bonds an atom can form is determined by its valence electrons.
• The shape of a covalent molecule affects its properties.
• Covalent compounds have distinct properties that differ from ionic compounds.

Practice Questions:

1. Draw the Lewis structure of ammonia (NH?) and explain the type of covalent bond formed.
2. Describe the difference in the properties of water and methane and relate this to their molecular structures.
3. Why are covalent compounds poor conductors of electricity?

Conclusion:

Understanding covalent bonding and molecular structures is crucial for grasping the behavior and properties of many common substances. By applying the knowledge of electron sharing and bonding patterns, you can predict the characteristics and reactivity of a wide range of covalent compounds.