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Ionic bonding is electrostatic attraction between oppositely charged ions throughout a giant lattice. Metallic bonding attracts positive metal ions to delocalised electrons. A covalent bond contains a shared electron pair; in a coordinate bond both electrons originated from one atom. Giant covalent structures such as diamond require many strong covalent bonds to break on melting. A simple molecular substance usually melts by overcoming intermolecular attractions, leaving the molecules themselves intact. Mobile charged particles explain electrical conduction, not the mere presence of charged particles.
Video by Eliot Rintoul. The video’s own board label is retained; follow the specification reference and scope notes on this lesson for assessed content.
Viewing focus: Relate ionic, covalent and metallic structures to properties
After watching, attempt these questions before opening the answers. You can also use the written lesson below.
After watching 1: What shape does NH3 have?
Trigonal pyramidal. Three bonds and one lone pair produce a pyramidal molecular shape.
After watching 2: What primarily breaks when iodine melts?
Intermolecular attractions. Iodine consists of simple I2 molecules.
What you'll be able to do
Ionic bonding is electrostatic attraction between oppositely charged ions throughout a giant lattice. Metallic bonding attracts positive metal ions to delocalised electrons. A covalent bond contains a shared electron pair; in a coordinate bond both electrons originated from one atom. Giant covalent structures such as diamond require many strong covalent bonds to break on melting. A simple molecular substance usually melts by overcoming intermolecular attractions, leaving the molecules themselves intact. Mobile charged particles explain electrical conduction, not the mere presence of charged particles.
Electron pairs around a central atom repel and arrange to minimise repulsion. Two bonding regions give a linear shape, three trigonal planar and four tetrahedral. Five and six bonding regions give trigonal bipyramidal and octahedral arrangements. A double bond counts as one region. Lone pairs repel more strongly than bonding pairs, compressing bond angles: methane is about 109.5°, ammonia about 107° and water about 104.5°. Name the molecular shape using the positions of atoms, not the invisible lone pairs.
Electronegativity is an atom’s ability to attract the shared pair in a covalent bond. A molecule may contain polar bonds but have no overall dipole if bond dipoles cancel by symmetry. All molecules have London forces; permanent dipoles add attractions. Hydrogen bonding requires hydrogen bonded to N, O or F interacting with a lone pair on an appropriate atom. Compare similar-sized molecules carefully: increasing electron number and contact area can make London forces stronger than a simplistic polarity-only prediction suggests.
Attempt these problems on paper before opening the worked reasoning. Explain your steps as well as giving a final answer.
Common mistakes to avoid
Key takeaways
Question 1: Why is CO2 non-polar while water is polar?
Shape determines whether bond dipoles cancel.
Check the assessed scope and practical or mathematical requirements.
An external explanation or interactive activity to use alongside the lesson. It may include extension material.
Close the notes and answer from memory. Revisit any explanation you cannot yet reconstruct.
Test yourself
Answer a few questions, then review anything you missed.
Start with the quiz above to check the key ideas. You can also choose another topic from the practice library.