3.5 Shapes of molecules

2 of 2 objectives have lessons · 0 studied · 0 secure

Lessons

VSEPR: electron pairs push apartElectron pairs around a central atom repel and get as far apart as possible, giving linear, trigonal planar, tetrahedral, trigonal bipyramidal and octahedral shapes. 5 min, not started
Lone pairs squeeze bond angles: NH₃ and H₂OLone pairs repel more strongly than bonding pairs, so NH₃ is pyramidal (107°) and H₂O is non-linear (104.5°), not tetrahedral like CH₄ (109.5°). 5 min, not started
Predicting the shape of any molecule or ionA five-step electron count gives the bonding pairs and lone pairs on a central atom, so you can predict the shapes and angles of molecules and ions like NH₄⁺, H₃O⁺ and PCl₆⁻. 5 min, not started
Shapes with double bonds and more than one centreCount a double or triple bond as one region and work out the shape around each central atom in turn, as in C₂H₄, C₂H₆, HCN, SO₂ and CH₃OH. 5 min, not started

Syllabus objectives

2 objectives

What Cambridge says you should be able to do, in our words. Codes are the topic number plus the objective’s position.

3.5.1

State and explain the shapes of, and bond angles in, molecules using VSEPR theory, including as simple examples: BF₃ (trigonal planar, 120°), CO₂ (linear, 180°), CH₄ (tetrahedral, 109.5°), NH₃ (pyramidal, 107°), H₂O (non-linear, 104.5°), SF₆ (octahedral, 90°) and PF₅ (trigonal bipyramidal, 120° and 90°).

Taught in: Shapes with double bonds and more than one centre, Lone pairs squeeze bond angles: NH₃ and H₂O, VSEPR: electron pairs push apart · 15 questions

3.5.2

Predict the shapes of, and bond angles in, molecules and ions analogous to those specified in 3.5.1.

Taught in: Shapes with double bonds and more than one centre, Predicting the shape of any molecule or ion · 13 questions