S2.2 The covalent modelIB Chemistry HL: Flashcards

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How do bond length and bond strength change with bond order?

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How do bond length and bond strength change with bond order?: More shared pairs: shorter and stronger bonds.
Shape of NH₃ and its bond angle?: Trigonal pyramidal, about 107°.
Order of intermolecular forces for comparable molar mass?: London < dipole–dipole < hydrogen bonding.
(HL) Shape of SF₄?: Seesaw (five domains, one lone pair).
(HL) Shape of ClF₃?: T-shaped (five domains, two lone pairs).
(HL) Shape of XeF₄?: Square planar (six domains, two lone pairs).
(HL) Shape of BrF₅?: Square pyramidal (six domains, one lone pair).
(HL) Formula for formal charge?: FC = valence electrons − non-bonding electrons − ½ bonding electrons.
(HL) How do you choose the preferred Lewis formula?: Formal charges closest to zero; any negative charge on the most electronegative atom.
(HL) What are resonance structures?: Lewis formulas with the same atom positions but different positions of double bonds; the real structure is a hybrid.
(HL) Give two pieces of evidence for delocalisation in benzene.: All C–C bonds are 0.140 nm; hydrogenation is ~152 kJ mol⁻¹ less exothermic than predicted (also: substitution, one 1,2-isomer).
(HL) Difference between σ and π bonds?: σ: head-on overlap, density along the axis. π: sideways p-orbital overlap, density above and below the axis.
(HL) σ and π bonds in a triple bond?: One σ and two π.
(HL) Hybridisation of a carbon with three electron domains?: sp² (trigonal planar, 120°).