#6 Shapes Of Molecules And Intermolecular Forces

Question 1

Describe a linear shape?

Answer 1

2 bonded pairs
0 lone pairs
180• bond angel

Question 2

Describe a trigonal planar shape?

Answer 2

3 bonded pairs
0 lone pairs
120• bond angle

Question 3

Describe a tetrahedral shape?

Answer 3

4 bonded pairs
0 lone pairs
109.5• bond angle

Question 4

Describe an octahedral shape?

Answer 4

You’d think 8 but no no no

6 bonded pairs
0 lone pairs
90• bond angle

Question 5

Describe a non-linear shape?

Answer 5

2 bonded pairs
2 lone pairs
104.5•

Question 6

Describe a pyramidal shape?

Answer 6

3 bonded pairs
1 lone pair
107• bond angle

Question 7

Which repel more bones pairs or lone pairs?

Answer 7

Lone pairs of electrons repel more than bonded pairs

Question 8

State and explain the bond angle in an ammonia molecule?

Answer 8

-Electron pairs repel, so get as far away as possible
-NH3 has 1 lone pair and 3 bonded pairs of electrons
-Lone pair repel more that bonded pairs so the bond angle is 107•, with a pyramidal shape

Question 9

What to always include in an answer about shape and bond angle?

Answer 9

-shape
-bond angle
-electron pairs repel
-lone pairs repel more than bonded
-how many lone and bonded pairs

Question 10

What bonds form due to varying electronegativities?

Answer 10

-Large diff in electronegativity between atoms= ionic bonds form
-no difference= covalent bond
-in between= polar covalent (result in dipole) (ie delta charges)
H and C have similar elcetronegativities

Question 11

Most electronegative elements?

Answer 11

F
O
Cl
N

Question 12

What do polar bonds have?

Answer 12

A permanent dipole

Question 13

Fill in the blank: dipoles must not_____.

Answer 13

Oppose and cancel one another

Question 14

What is a net dipole?

Answer 14

When one end of the molecule is delta - and the other delta + therefore there is a net dipole= polar molecule

Question 15

What are the 3 intermolecular forces?

Answer 15

-Induced dipole-dipole interactions (London forces)
-permanent dipole-dipole interactions (polar molecules)
-hydrogen bonding (H-F, H-O, H-N bonds only)

Question 16

Out of the 3 intermolecular forces which one is the strongest and weakest?

Answer 16

Strongest= Hydrogen bonding
Weakest= Induced dipole-dipole interactions (London forces)

Question 17

Out of the 3 intermolecular forces which are van der waals forces?

Answer 17

-permanent dipole-dipole (polar molecules)
-Induced dipole-dipole (London forces)

Question 18

How do London forces form?

Answer 18

Uneven distribution of electrons creates a temporary instantaneous dipole which causes induced dipoles on neighbouring molecules

Question 19

What makes a London forces (induced dipole-dipole)

Answer 19

-Bigger molecule (higher Mr) as more electrons result in larger induced dipole-dipole interactions
-greater surface area between molecules ie:

Question 20

What interactions does a polar molecule have?

Answer 20

-permanent dipole
-induced dipoles/ London forces

Question 21

True or false: everything has london forces

Answer 21

True: everything has London forces some have additional forces

Question 22

Why is F-F non polar?

Answer 22

Same charge
Symmetrical
Electrons attracted equally

Question 23

What are the only elements that can form hydrogen bonds? Why?

Answer 23

Fluorine
Nitrogen
Oxygen
Because they are the most electronegative

Question 24

What is hydrogen bonding?

Answer 24

Intermolecular bonding between H and N or O or F

Question 25

Draw hydrogen bonding in water?

Answer 25

Question 26

Draw hydrogen bonding in ammonia?

Answer 26

Question 27

Why is ice less dense than water?

Answer 27

-Hydrogen bonds holding the water molecules apart in an open lattice structure -water molecules in ice are further apart than in liquid water

Question 28

Why does water have a relatively high melting/boiling 0 Point?

Answer 28

-Hydrogen bonds contribute extra forces that need to be overcome to melt of boil water -More energy required to overcome these forces

Question 29

Ice forms an ____ lattice.

Answer 29

Open

Question 30

What is a simple molecular lattice?

Answer 30

Covalent bonded molecules attracted by intermolecular forces

Question 31

Ionic bonds are very strong and form______.

Answer 31

A giant lattice

Question 32

Covalent bond are very strong and form _____.

Answer 32

Small molecules/ giant lattice

Question 33

Are the melting/boiling points of simple molecular lattices high or low? Why?

Answer 33

Low: weak intermolecular forces break, not much energy required to melt/boil

Question 34

Do simple molecular lattices conduct electricity?

Answer 34

No: no mobile charge carriers (ions)

Question 35

How to use electron pairs to predict the shapes of molecules?

Answer 35

1.work out the no. Electrons in outer shell of central atom (use periodic table) 2.use molecular formula to find how many atoms the central molecule is bonded to 3. Add up the electrons and divide by 2 to find no. Electron pairs on central atom. If it an ion account for its charge 4.compare no. Electron pairs with no. Bonds to find no. Lone pairs (if there a double bond count it as 2 bonds) 5.use the no. Electrons pairs and lone pairs of central atom to work out shape and angle

Question 37

What is a dipole?

Answer 37

A dipole is a difference in charge between the two atoms caused by a shift in electron density in the bond