← Bonding, structure, properties and energy changes

Lewis structures & VSEPR (every paper)

Draw → count regions → name shape → angle. Lone pairs squeeze.

Regions	LP	Shape	Angle	Example
4	0	Tetrahedral	109.5°	CH₄
4	1	Trigonal pyramidal	~107°	NH₃
4	2	Bent	~104.5°	H₂O
3	0	Trigonal planar	120°	BF₃
2	0	Linear	180°	CO₂

Double bonds = ONE region. Show every lone pair.

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The angle question

Shape name = Achieved. Merit is why: lone pairs repel more than bonding pairs, closing the angle below 109.5°. ℹ

Parent geometry versus final molecular shape

The PARENT geometry is decided by the total number of electron-density regions arranging for maximum separation (e.g. 4 regions → tetrahedral parent). The FINAL molecular shape only counts the BONDING regions — a lone pair still occupies space and affects the angle, but is not itself "seen" in the shape's name. This distinction (parent geometry vs final shape) is exactly what separates a correct shape name from a correct explanation of why that shape follows from the electron count.

Practice for this standard covers the whole topic — flashcards and quiz.