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Formula Sheets / Chemistry

Chapter 4

Chemical Bonding and Molecular Structure

Revise with flashcards Download this chapter (PDF) All Chemistry formulas (PDF)

Lewis structures and formal charge VSEPR and hybridisation Molecular orbital theory Ionic bonding and Fajans' rules Hydrogen bonding

Lewis structures and formal charge

Formal charge
FC $= V - L - \frac{1}{2} B (V =$ valence $, L =$ lone-pair electrons $, B =$ bonding electrons $)$

VSEPR and hybridisation

Steric number
SN $= \frac{1}{2} (V + M - c + a)$
$V$ valence electrons of the central atom, $M$ monovalent atoms around it, $c$ / $a$ positive / negative charge.
Hybridisation from SN
$2 s p, 3 s p^{2}, 4 s p^{3}, 5 s p^{3} d, 6 s p^{3} d^{2}, 7 s p^{3} d^{3}$
Repulsion order
lp–lp $>$ lp–bp $>$ bp–bp
Dipole moment
$μ = q \times d;$ $1$ D $= 3.336 \times 1 0^{- 30}$ C m
% ionic character
$\frac{μ _{observed}}{μ _{ionic}} \times 100$

Molecular orbital theory

Bond order
BO $= \frac{1}{2} (N_{b} - N_{a});$ BO $↑\Rightarrow$ bond length $↓,$ bond energy $↑$
Filling order
$\leq 14 e^{-} : σ 1 s, σ^{*} 1 s, σ 2 s, σ^{*} 2 s, π 2 p_{x} = π 2 p_{y}, σ 2 p_{z}, \dots;$ $> 14 : σ 2 p_{z}$ before $π 2 p$
Paramagnetic examples
O $_{2} (2$ unpaired $),$ B $_{2},$ O $_{2}^{+},$ O $_{2}^{-},$ N $_{2}^{+}$

Ionic bonding and Fajans' rules

covalent character $↑$ with small cation, large anion, high charge, and $(n - 1) d^{n} n s^{0}$ cations

Hydrogen bonding

intermolecular: raises boiling point (H $_{2}$ O, HF, NH $_{3}$ ) $;$ intramolecular: lowers it (o-nitrophenol)

Classification of Elements and Periodicity in Properties Thermodynamics