shapes of molecules and intermolecular forces- chapter 6

Question 1

what is the electron-pair repulsion theory

Answer 1

a model used in chemistry for explaining and predicting the shapes of molecules and polyatomic ions

• the electron pairs surrounding a central atom determine the shape of the molecule or ion
• the electron pairs repel one another so that they are arranged as far apart as possible
• the greater the number of electron pairs, the smaller the bond angle
• lone pairs of electrons repel more strongly than bonded pairs
• different numbers of electron pairs result in different shapes

Question 2

what does a solid line represent

what does a solid wedge represent

what does a dotted wedge represent

Answer 2

a bond in the plane of the paper

comes out of the plane of the paper

goes into the plane of the paper

Question 3

what is the order of relative repulsion’s between lone pairs and bonding pairs

Answer 3

bonded-pair/bonded-pair < bonded-pair/lone-pairs < lone-pair/lone-pair

Question 4

why do lone pairs repel more strongly

Answer 4

as lone pair of electrons is slightly closer to the central atom and occupies more space than a bonded pair, which results in the lone pair repelling stronger

Question 5

how is the bond angle reduced

what is it reduced by

Answer 5

the 4 electron pairs around the central atom repel one another as far apart as possible into a tetrahedral arrangement

lone pairs repel more strongly that bonded

therefore, lone pairs repel bonded pairs slightly closer together, decreasing the bond angle

reduced by 2.5

Question 6

how many bonded pairs, lone pairs and bond angle in:

a. tetrahedral
b. pyramidal
c. non-linear

Answer 6

a. 4, 0, 109.5

b. 3, 1, 107

c. 2, 2, 104.5

Question 7

explain the molecular shape from multiple bonds (carbon dioxide example)

Answer 7

each multiple bond is treated as a bonding region

the 4 bonded pairs around the central carbon atom are arranged as two double bonds, which count as two bonded region

the two bonded region repel one another as far apart as possible, this give the carbon dioxide molecule a linear shape with all three atoms aligned in a straight line

Question 8

what is the electron pairs/regions and bond angle of

a. linear
b. trigonal planar
c. tetrahedral
d. octahedral

Answer 8

a. 2, 180

b. 3, 120

c. 4, 109.5

d. 6, 90