Valence Shell Electron Pair Repulsion (VSEPR Shapes)

Vocabulary flashcards covering VSEPR shapes, electron pair geometry, ABE notation, bond angles, polarity rules, and hybridization.

VSEPR

Valence Shell Electron Pair Repulsion; a model used to predict the geometries and shapes of molecules based on electron pair repulsion around a central atom.

"ABE" Notation

A classification scheme where "A" denotes the central atom, "B" denotes the number of bonded peripheral atoms, and "E" denotes the number of lone pairs on the central atom.

Linear ($AB_2$)

A molecular shape with 2 electron domains ($B+E = 2$), linear electron pair geometry, a bond angle of $180^\text{o}$, $sp$ hybridization, and polarity dictated by the electronegativity of peripheral atoms.

Trigonal Planar ($AB_3$)

A molecular shape with 3 electron domains ($B+E = 3$), trigonal planar electron pair geometry, bond angles of $120^\text{o}$, $sp^2$ hybridization, and polarity dictated by the electronegativity of peripheral atoms.

Angular ($AB_2E$)

A molecular shape with 3 electron domains ($B+E = 3$), trigonal planar electron pair geometry, 1 lone pair, a bond angle of $117.5^\text{o}$, $sp^2$ hybridization, and is ALWAYS polar due to the lone pair of electrons.

Tetrahedral ($AB_4$)

A molecular shape with 4 electron domains ($B+E = 4$), tetrahedral electron pair geometry, bond angles of $109.5^\text{o}$, $sp^3$ hybridization, and polarity dictated by the electronegativity of peripheral atoms.

Trigonal Pyramidal ($AB_3E$)

A molecular shape with 4 electron domains ($B+E = 4$), tetrahedral electron pair geometry, 1 lone pair, a bond angle of $107^\text{o}$ ($107.3^\text{o}$), $sp^3$ hybridization, and is ALWAYS polar due to the lone pair of electrons.

Bent ($AB_2E_2$)

A molecular shape with 4 electron domains ($B+E = 4$), tetrahedral electron pair geometry, 2 lone pairs, a bond angle of $104.5^\text{o}$, $sp^3$ hybridization, and is ALWAYS polar because electron pairs DO NOT cancel each other.

Trigonal Bipyramidal ($AB_5$)

A molecular shape with 5 electron domains ($B+E = 5$), trigonal bipyramidal electron pair geometry, bond angles of $120^\text{o}$ and $90^\text{o}$, and polarity dictated by the electronegativity of peripheral atoms.

See Saw ($AB_4E$)

A molecular shape with 5 electron domains ($B+E = 5$), trigonal bipyramidal electron pair geometry, and 1 lone pair (which decreases bond angles); it is ALWAYS polar due to the lone pair of electrons.

T-Shaped ($AB_3E_2$)

A molecular shape with 5 electron domains ($B+E = 5$), trigonal bipyramidal electron pair geometry, and 2 lone pairs; it is ALWAYS polar because the electron pairs DO NOT cancel each other.

Linear ($AB_2E_3$)

A molecular shape with 5 electron domains ($B+E = 5$), trigonal bipyramidal electron pair geometry, and 3 equatorial lone pairs; electron pairs CANCEL each other, so polarity is dictated by the electronegativity of peripheral atoms.

Octahedral ($AB_6$)

A molecular shape with 6 electron domains ($B+E = 6$), octahedral electron pair geometry, bond angles of $90^\text{o}$, and polarity dictated by the peripheral atoms.

Square Pyramidal ($AB_5E$)

A molecular shape with 6 electron domains ($B+E = 6$), octahedral electron pair geometry, and 1 lone pair (which decreases bond angles); it is ALWAYS polar due to the lone pair of electrons.

Square Planar ($AB_4E_2$)

A molecular shape with 6 electron domains ($B+E = 6$), octahedral electron pair geometry, and 2 lone pairs; electron pairs CANCEL each other, making polarity dictated by the electronegativity of peripheral atoms.

Effect of Adding Lone Pairs on Bond Angles

In molecular geometries with 5 or 6 electron domains (such as trigonal bipyramidal or octahedral geometries), adding lone pair(s) decreases bond angles.