Molecules: Shapes & Forces PHYSICAL

Question 1

What theory predicts the shape and bond angles of molecules?

Answer 1

Valence Shell Electron Pair Repulsion (VSEPR)

Question 2

What are the rules of the Valence Shell Electron Pair Repulsion (VSEPR) theory?

Answer 2

Valence shell electrons are electrons found in outer shell
Electron pairs repel each other as they are of the same charge
Lone pair electrons repel each other more than bonded pairs
Repulsion between multiple and single bonds is treated same as for repulsion between single bonds
Repulsion between pairs of double bonds is greater
Most stable shape is adopted to minimize repulsion forces

Question 3

What is the order of repulsion for different pairs of electrons?

Answer 3

lone pair-lone pair
lone pair-bond pair
bond pair-bond pair

Question 4

Name the different shapes molecules can adopt.

Answer 4

Linear
Trigonal planar
Non-linear
Pyramidal
Tetrahedral
Trigonal bipyramidal
Octahedral

Question 5

What bond angle is present in Linear shape?

Answer 5

180 degrees

Question 6

What bond angle is present in Trigonal Planar?

Answer 6

120 degrees

Question 7

What bond angle is present in Non-Linear?

Answer 7

104.5 degrees

Question 8

What bond angle is present in Pyramidal?

Answer 8

107 degrees

Question 9

What bond angle is present in Tetrahedral?

Answer 9

109.5 degrees

Question 10

What bond angle is present in Trigonal Bipyramidal?

Answer 10

120 degrees
90 degrees

Question 11

What bond angle is present in Octahedral?

Answer 11

90 degrees

Question 12

What does a Linear shape contain?

Answer 12

2 electron groups
2 bonding groups
0 lone pairs

OR

5 electron groups
2 bonding groups
3 lone pairs

Question 13

What does a Trigonal Planar shape contain?

Answer 13

3 electron groups
3 bonding groups
0 lone pairs

Question 14

What does a Non-Linear shape contain?

Answer 14

4 electron groups
2 bonding groups
2 lone pairs

Question 15

What does a Tetrahedral shape contain?

Answer 15

4 electron groups
4 bonding groups
0 lone pairs

Question 16

What does a Trigonal Pyramidal shape contain?

Answer 16

4 electron groups
3 bonding groups
1 lone pairs

Question 17

What does a Trigonal Bipyramidal shape contain?

Answer 17

5 electron groups
5 bonding groups
0 lone pairs

Question 18

What is electronegativity?

Answer 18

The power of an atom to attract the pair of electrons in a covalent bond toward itself

Question 19

Why would electron distribution be unsymmetrical in a covalent bond?

Answer 19

Due to difference in electronegativity

Question 20

What is the most electronegative element in the periodic table?

Answer 20

Fluorine

Question 21

What factors affect electronegativity?

Answer 21

Nuclear charge
Atomic radius
Shielding

Question 22

How does nuclear charge affect electronegativity?

Answer 22

Increase in proton number leads to increase in nuclear attraction
Increased nuclear cahrge results in increased electronegativity

Question 23

How does atomic radius affect electronegativity?

Answer 23

Further electrons are less strongly attracted towards the nucleus
Increased atomic radius results in decreased electronegativity

Question 24

What is atomic radius?

Answer 24

Distance between nucleus and electrons in outer shell

Question 25

How does shielding affect electronegativity?

Answer 25

Fillled energy levels cause outer electrons to be less attracted to nucleus Increased number of shells results in decreased electronegativity

Question 26

What trend is seen in electronegativity going down groups?

Answer 26

Decreases down the group

Question 27

Why does electronegativity decrease down group?

Answer 27

Nuclear charge increases Shielding increases Large atomic radius Overall decrease in attraction

Question 28

What trend is seen in electronegativity going across periods?

Answer 28

Increases across period

Question 29

Why does electronegativity increase across period?

Answer 29

Nuclear charge increases Shielding remains similar Smaller atomic radius Overall increase in attraction

Question 30

What are intramolecular forces?

Answer 30

Forces within a molecule

Question 31

What type of bond is an intramolecular force?

Answer 31

Covalent

Question 32

What are intermolecular forces?

Answer 32

Forces between molecules

Question 33

What are the types of intermolecular forces?

Answer 33

Induced dipole-dipole (Van Der Waals) Permanent dipole-dipole Hydrogen bonding

Question 34

Which is stronger, intramolecular or intermolecular forces?

Answer 34

Intramolecular

Question 35

Name the types of intermolecular force ordered from strongest to weakest.

Answer 35

Hydrogen bonding Permanent dipole-dipole Induced dipole-dipole (Van der Waals)

Question 36

When is a covalent bond non-polar?

Answer 36

When the two atoms have the same electronegativity

Question 37

When is a covalent bond polar?

Answer 37

When the two atoms have different electronegativities and so electrons are drawn towards more electronegative atom

Question 38

What charge is a less electronegative atom given?

Answer 38

δ+ delta positive

Question 39

What charge is a more electronegative atom given?

Answer 39

δ- delta negative

Question 40

What determines the polarity of a bond?

Answer 40

The difference in electronegativity The greater the difference, the more polar the bond

Question 41

What type of dipoles do polar molecules have?

Answer 41

Permanent dipoles so permanent dipole-dipole forces

Question 42

Where do intermolecular forces occur between polar molecules?

Answer 42

The δ+ end of dipole in one molecule and the δ- end of dipole in a neighbouring molecule are attracted towards each other

Question 43

Where do induced dipole-dipole forces exist?

Answer 43

Between all atoms and molecules

Question 44

How do induced dipole-dipole forces exist?

Answer 44

Electron charge cloud in non-polar molecules is constantly moving During movement, a temporary dipole can form when electron cloud distorted The temporary dipole can iduce dipole on neighbouring molecules

Question 45

Which species allow hydrogen bonding?

Answer 45

Oxygen Nitrogen Fluorine

Question 46

Why does hydrogen bonding only occur with O, N and F?

Answer 46

The species must be very electronegative

Question 47

What can happen to H in hydrogen bonding?

Answer 47

Becomes so δ+ charged forms bond with lone pair of O, N or F atom in another molecule

Question 48

Name the properties of water.

Answer 48

High melting and boiling point High surface tension

Question 49

Why does water have high melting and boiling points?

Answer 49

Strong intermolecular forces of H bonding Large amount of energy needed to break bonds

Question 50

What is surface tension?

Answer 50

The ability of a liquid surface to resist external forces

Question 51

Why does water have high surface tension?

Answer 51

Water molecules at surface are bonded to other water molecules by H bonds Pull downwards on surface molecules causing the surface to become compressed and tightly packed

Question 52

Why are solids denser than liquids?

Answer 52

Particles in solids more closely packed than liquids

Question 53

Why does ice have lower density than water?

Answer 53

Water molecules packed into open lattice Hydrogen bonds have long bond length Water molecules slightly further apart than in liquid form