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Covalent bonding is the sharing of pairs of electrons between atoms, and electron pairs repel to set molecular shapes. Free notes and 11 questions answered.
Chemical Bonding and Molecular Shapes is part of Key ideas in GCSE AQA Higher Chemistry.
4 min
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GCSE AQA Higher
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Covalent bonding is the sharing of pairs of electrons between atoms, and electron pairs repel to set molecular shapes. Free notes and 11 questions answered.
Use this lesson to stay inside Key ideas while connecting the detail back to the wider Topic 11: Key ideas topic.
Read the core explanations from Chemical Bonding and Molecular Shapes before testing yourself from memory.
Picture an atom as a person desperately wanting to feel complete. Most atoms have incomplete outer electron shells, making them unstable and reactive. They'll do almost anything to get a full outer shell - either 2 electrons (like helium) or 8 electrons (like the other noble gases).
Atoms achieve this stability in three ways: they can steal electrons, share electrons, or pool their electrons together. These three strategies create the three types of chemical bonding that explain why materials behave so differently.
When a metal meets a non-metal, it's like a generous person meeting someone in need. The metal atom has loosely held outer electrons it's happy to give away. The non-metal desperately wants electrons to fill its outer shell.
When sodium (Na) meets chlorine (Cl), sodium gives up its single outer electron. This creates Na⁺ (positive ion) and Cl⁻ (negative ion). Opposite charges attract strongly, forming an ionic bond.
When two non-metals meet, neither wants to give up electrons. Instead, they share. This creates covalent bonds - the strongest type of chemical bond between individual atoms.
In water (H₂O), each hydrogen shares its electron with oxygen, whilst oxygen shares one of its electrons back. This creates two covalent bonds. The shared electrons spend time around both nuclei, holding the atoms together.
Covalent compounds can form small molecules (like water) or giant covalent structures (like diamond). The bonding is the same - shared electrons - but the scale is completely different.
Metals take a completely different approach. Instead of hoarding electrons like non-metals, metal atoms release their outer electrons into a shared 'sea' that flows around all the metal ions.
This electron sea explains why metals conduct electricity (electrons can flow) and why they're malleable (layers can slide over each other without breaking bonds). The bonding isn't directional like covalent bonds.
Once atoms bond, the shape of the resulting molecule determines how it behaves. Electron pairs repel each other, so they arrange themselves as far apart as possible in three-dimensional space.
Water is bent (not straight) because oxygen has two bonding pairs and two lone pairs of electrons. The lone pairs take up more space, pushing the hydrogen atoms closer together at 104.5°.
Methane (CH₄) is tetrahedral because four bonding pairs arrange themselves equally in 3D space, creating bond angles of 109.5°. This shape minimises electron pair repulsion.
Bonding questions appear in every GCSE chemistry paper. Examiners test whether you can link bonding type to properties, not just memorise definitions.
Common exam mistakes include confusing intermolecular forces with chemical bonds, and thinking all covalent substances have low melting points. Giant covalent structures like diamond have very high melting points because you're breaking covalent bonds, not weak intermolecular forces.
Exam precision note: In Chemical Bonding and Molecular Shapes - Key ideas - Key ideas, always identify the key chemical idea first, then link it to evidence, data, or an equation. A high-scoring GCSE answer names the particles involved, states what changes, and justifies the conclusion using correct scientific language. Where calculations are used, show each step with units and keep significant figures sensible. Finally, check that terminology matches AQA wording so your answer is unambiguous and mark-scheme friendly.
Worked example: Step-by-Step: Structured Chemistry Explanation
Answer a GCSE-style question in Chemical Bonding and Molecular Shapes - Key ideas - Key ideas using precise terminology.
Answer: High-quality answers combine principle, application, and a precise conclusion.
Proton transfer is another way particles can interact in chemistry. In acid-base reactions, an acid can donate H+ ions and a base can accept them. This is not a bonding type like ionic, covalent, or metallic bonding, but it is still an important particle-level idea because it explains why acids react the way they do. A concise mention here helps students connect bonding ideas with later acid-base chemistry.
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Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.
Covalent bonding is the sharing of pairs of electrons between atoms to achieve stable electron configurations, typically between non-metal atoms. Covalent compounds can form small molecules, like water, or giant covalent structures, like diamond.
Electron pair repulsion theory says electron pairs repel each other, so they arrange themselves as far apart as possible in three-dimensional space. This predicts molecular shapes, such as tetrahedral methane at 109.5° and bent water at 104.5°, where lone pairs take up more space.
Atoms form bonds to get a full outer shell, because most atoms have incomplete outer electron shells, which makes them unstable and reactive. A full outer shell has 2 electrons, like helium, or 8 electrons, like the other noble gases.
When sodium meets chlorine, sodium gives up its single outer electron to chlorine, forming Na⁺ and Cl⁻ ions. The oppositely charged ions attract strongly, and this electrostatic attraction is the ionic bond.
Methane, CH₄, is tetrahedral because its four bonding pairs of electrons arrange themselves equally in 3D space. This gives bond angles of 109.5° and minimises electron pair repulsion.
Water is bent because oxygen has two bonding pairs and two lone pairs of electrons. Electron pairs repel each other, and the lone pairs take up more space, pushing the hydrogen atoms closer together at 104.5°.
The three types of chemical bonding are ionic, covalent and metallic. In ionic bonding, electrons transfer from metal to non-metal atoms; in covalent bonding, non-metal atoms share pairs of electrons; and in metallic bonding, metal atoms pool their outer electrons into a delocalised sea.
Metals conduct electricity because their delocalised sea of electrons can flow throughout the metal structure. They are malleable because layers of metal ions can slide over each other without breaking bonds, since metallic bonding is not directional like covalent bonds.
Not all covalent substances have low melting points; thinking so is a common mistake. Giant covalent structures like diamond have very high melting points because melting them means breaking covalent bonds, not weak intermolecular forces.
Proton transfer is not a bonding type like ionic, covalent or metallic bonding. It is a way particles interact in acid-base reactions, where an acid can donate H+ ions and a base can accept them, which explains why acids react the way they do.
Small molecules like water and giant covalent structures like diamond both have the same bonding, shared electrons, but on completely different scales. Diamond has a very high melting point because covalent bonds must break, whereas small molecules are held together only by weak intermolecular forces.