AP Chemistry Unit 2

VSEPR

VSEPR

Valence Shell Electron Pair Repulsion Theory

predicts the geometries of molecules and polyatomic ions

What does VSEPR do?

Lone pair-Lone pair > Lone pair-Bonding pair > Bonding pair-bonding pair

What has the strongest repulsion (ranked greatest to least)?

Linear

2 bonding pairs, 0 lone pairs, 180º

Trigonal Planar

3 bonding pairs, 0 lone pairs, 120º

Bent

2 bonding pairs, 1 lone pair, <120

Tetrahedral

4 bonding pairs, 0 lone pairs, 109.5º

Trigonal Pyramidal

3 bonding pairs, 1 lone pair, 107.5º

Bent

2 bonding pairs, 2 lone pairs, 104.5º

Trigonal Bipyramidal

5 bondings pairs, 0 lone pairs

Seesaw

4 bonding pairs, 1 lone pair

T-shaped

3 bonding pairs, 2 lone pairs

Linear

2 bonding pairs, 3 lone pairs

Octahedral

6 bonding pairs, 0 lone pairs

Square pyramidal

5 bonding pairs, 1 lone pairs

Square Planar

4 bonding pairs, 2 lone pairs

a shared pair of electrons forming a single covalent bond

Line or pair of dots between two atoms represents…

two shared pairs of electrons forming a double bond

Two lines or 4 dots between two atoms represents…

three shared pairs of electrons forming a tribple bond

Three lines or 6 dots between two atoms represents…

Lone pair

A pair of electrons in a single atom

1. Determine # of valence electrons of all atoms in molecule (look at periodic table)

2. Draw the skeleton (Least electronegative element as the central atom, other atoms are terminal atoms, place a single bond between each terminal atom and the central atom, Elements in period 3 can have an expanded octet so more than 8 electrons on the central atom)

3. Place remaining electrons as lone pairs to complete octet on each atom (place lone pairs on terminal atoms first, then central atom)

4. Check to make sure all atoms have a complete octet of electrons (if the central atom does not have a full octet, add double or triple bonds as needed *NOTE:  hydrogen or halogens will never have multiple bonds)

Steps for drawing Lewis Structure:

Octet

8 electrons