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VICChemistryQuick questions
Unit 1: How can the diversity of materials be explained?
Quick questions on Intermolecular forces and covalent substances: VCE Chemistry Unit 1
15short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What is intermolecular forces (IMFs)?Show answer
Intermolecular forces are attractions between molecules, not within them. Breaking an IMF (boiling or melting a molecular substance) takes far less energy than breaking the covalent bonds inside a molecule.
What is predicting boiling points?Show answer
Apply this order of decisions:
What is three classes of covalent material?Show answer
Covalent molecular substances. Discrete molecules held together by IMFs in the solid and liquid states. Examples: water (H2O), sucrose (C12H22O11), iodine (I2), CO2 (dry ice). Properties:
What is allotropes of carbon?Show answer
Allotropes are different structural forms of the same element. Carbon has several worth knowing:
What is 1. Dispersion forces?Show answer
Present between all molecules (and atoms). They arise from instantaneous, fluctuating dipoles in the electron cloud of one molecule inducing a dipole in a neighbour. Strength increases with the number of electrons (and surface area).
What is 2. Dipole-dipole attractions?Show answer
Present only between polar molecules. The partial positive end of one molecule attracts the partial negative end of another. Stronger than dispersion (for molecules of similar size), but weaker than hydrogen bonds.
What is 3. Hydrogen bonding?Show answer
A special, particularly strong dipole-dipole interaction. Requires all three of:
What is covalent molecular substances?Show answer
Discrete molecules held together by IMFs in the solid and liquid states. Examples: water (H2O), sucrose (C12H22O11), iodine (I2), CO2 (dry ice). Properties:
What is covalent network substances?Show answer
Every atom in the solid is bonded covalently to its neighbours in a 3D giant lattice. There are no discrete molecules. Examples: diamond, silicon dioxide (quartz), silicon carbide.
What is covalent layered substances?Show answer
Atoms within a layer are covalently bonded, but layers themselves are held together by weak dispersion forces. The standout example is graphite.
What is confusing intermolecular and intramolecular forces?Show answer
Boiling water breaks IMFs (hydrogen bonds), not the O-H covalent bonds. Water vapour is still H2O.
What is calling all polar molecules hydrogen bonded?Show answer
HCl is polar but does not hydrogen bond (Cl is too large and not electronegative enough; only N, O, F qualify).
What is forgetting that all molecules have dispersion forces?Show answer
Non-polar molecules have only dispersion. Polar molecules have dispersion plus dipole-dipole.
What is saying graphite has no covalent bonds because the layers slide?Show answer
Within each layer the bonding is strong covalent. The layers slide because the layer-to-layer force is weak dispersion.
What is calling diamond a metal because it is hard?Show answer
Diamond is a covalent network, not metallic. It does not conduct.