VSEPR Theory

Question 1

VSEPR Theory

Valence Shell Electron-Pair Repulsion

Answer 1

• used to predict the shape of a molecule based on # of e-charged clouds (lone pairs of ve-) on a given atom
• e-clouds will arrange themselves to be as far away as possible from each other
• reduces repulsion
• for cov-bond compounds only

Question 2

Electron Groups

Answer 2

Are lone pairs and # of bonded atoms (even it they’re single/double/triple bonds)

Question 3

2 Electron Groups
Single Bonds
Linear (180)

Answer 3

• central atom + 2 outer atoms on either side
• outer atoms have same # of lone pairs & equal electronegativity
• dipole arrows are pointing in opp directions from central atom (cancel)
• arrangement of 2 e-groups is 180, opp each other (linear)

Question 4

2 E-groups
Double Bonds
Linear (180)

Answer 4

• central atom + 2 outer atoms
• outer atoms have same # of lone pairs & equal electronegativity
• dipole arrows point in opp directions
• arrangement of 2 e-groups is 180

Question 5

2 E-groups + 1 Lone Pair
Single Bonds
Trigonal Planar Arrangement (120)

Answer 5

• central atom has lone pair, outer atoms have achieved octet (positive)
• dipoles point to central from outer due to octet + central lone pair
• lone pair pushes outer atoms away
• trigonal planar arrangement (bent) 120

Question 6

2 Bonding Atoms + 2 Lone Pairs
Single Bonds
Tetrahedral (109)

Answer 6

• bonded outer atoms to central has 2 lone pairs adjacent each other
• tetrahedral arrangement (bent) 109
  eg. H2O

Question 7

3 E-groups
Single Bonds
Trigonal Planar

Answer 7

• 3 e-groups bonded to central atom
• repulsion is minimized w/3 e-groups at angles of 120
• trigonal planar

Question 8

3 Bonding Atoms + 1 Lone Pair
Single Bonds
Pyramidal (109)

Answer 8

• 3 outer atoms bonded to central atom w/lone pair
• repulsion minimized in tetrahedral arrangement
• 3 bonded atoms form the base corners for pyramidal shape (109)

Question 9

General Rules

Answer 9

• ID central atom
• draw chemical formula into Lewis structure
• note any lone pairs
• use electronegativity to determine delta charges of atoms
• draw dipole arrows to see if they cancel each other out
• note the number of corners/angles/points it has

Question 10

Polar Molecules

Answer 10

Have dipoles (electronegativity btwn 0.5-1.7) which do not point in opposite directions; does not cancel each other, thus one end is more negatively charged than the other.

Question 11

Non-polar Molecules

Answer 11

Contains non-polar bonds (electronegativity 0.4 and under)

-or has a symmetrical arrangement of polar bonds (dipoles cancel each other out).