Chapter 6-Shapes of Molecules and Intermolecular forces

Question 1

What does the shape of molecules depend on?

Answer 1

The total number of either bonded and lone electron pairs around the central atom.

Question 2

What is the rule for repulsion of electron pairs?

Answer 2

Electron pairs repel as far as possible but lone pairs repel more than bonding pairs.

Question 3

How do you represent different planes of bonds?

Answer 3

• Solid line-represents a bond in the plane of the paper
• Solid wedge-comes out of the plane of the paper
• Dotted wedge/line-goes into the plane of the paper

Question 4

2 electron pairs:
* Name the shape
* Give the bond angle

Answer 4

• Linear
• 180°

Question 5

3 Electron pairs (3 bonding pairs):
* Name the shape
* Give the bond angle

Answer 5

• Trigonal planar
• 120°

Question 6

3 Electron pairs (2 bonding pairs):
* Name the shape
* Give the bond angle

Answer 6

• Non-linear/V-shaped
• 118°

Question 7

4 Electron pairs (4 bonding pairs):
* Name the shape
* Give the bond angle

Answer 7

• Tetrahedral
• 109.5°

Question 8

4 Electron pairs (3 bonding pairs):
* Name the shape
* Give the bond angle

Answer 8

• Pyramidal
• 107°

Question 9

4 Electron pairs (2 bonding pairs):
* Name the shape
* Give the bond angle

Answer 9

• Non linear/V-shaped
• 104.5°

Question 10

6 Electron pairs (6 bonding pairs):
* Name the shape
* Give the bond angle

Answer 10

• Octahedral
• 90°

Question 11

6 Electron pairs (5 bonding pairs):
* Name the shape
* Give the bond angle

Answer 11

• Square pyramidal
• Bond angle-89°

Question 12

6 Electron pairs (4 bonding pairs):
* Name of shape
* Give the bond angle

Answer 12

• Square planar
• 90°

Question 13

What is electronegativity?

Answer 13

A measure of the tendency of an atom to attract a bonding pair of electrons in a covalent bond.

Question 14

What does increasing electronegativity of an atom impact?

Answer 14

It attract electrons towards that atom more.

Question 15

What did Linus Pauling invent?

Answer 15

The Linus Pauling scale measuring electronegativity of an atom from a scale of 0-4 where 4 is the most electronegative.

Question 16

What are the factors affecting Electronegativity?

Answer 16

• Nuclear charge
• Atomic radius
• Shielding

Question 17

Explain how nuclear charge impacts on electronegativity?

Answer 17

The more protons in the nucleus, the stronger attraction between the nucleus and bonding pair of electrons.

Question 18

Explain how atomic radius affects electronegativity?

Answer 18

The closer to the nucleus, the stronger the attraction between the nucleus and bonding pair of electrons.

Question 19

Explain how shielding impacts electronegativity?

Answer 19

Fewer shells of electrons between the nucleus and the electrons results in less shielding (repulsion) and stronger attracton between the nucleus and bonding pair of electrons.

Question 20

How and why does electronegativity change along a period?

Answer 20

Along a period electronegativity increases as the nuclear charge increases and the atomic radius decreases.

Question 21

How and why does electronegativity change down a group?

Answer 21

Down a group electronegativity decreases as the atomic radius increases and shielding increases.

Question 22

What causes a bond to be non polar?

Answer 22

When two atoms in a covalent bond have the same electronegativity.

Question 23

Explain what happens when two atoms in a covalent bond have different electronegativities?

Answer 23

• The covalent bond is polar
• Electrons are drawn to the more electronegative atom
• The less electronegative atom gets a partial charge of δ⁺
• The more electronegative atom gets a partial charge of δ⁻

Question 24

What increases bond polarity?

Answer 24

The greater the difference in electronegativity in a bond.

Question 25

What are the stages between a covalent and ionic bond? Give the electronegativity differences

Answer 25

* Pure covalent (0) * Polar covalent (0-1.8) * Polar ionic (1.8-4) * Pure ionic (4)

Question 26

What is the dipole moment?

Answer 26

A measure of how polar a bond is shown by --I----->

Question 27

Where does the dipole moment point?

Answer 27

The direction of the δ⁻ end of the molecule

Question 28

What constitutes a polar molecule?

Answer 28

Non-symmetrical molecules with polar bonds

Question 29

What are intermolecular forces?

Answer 29

Forces that hold molecules together where energy is required to overcome them when changing state.

Question 30

What are the three types of intermolecular forces in order of strength?

Answer 30

* London forces * Permanent dipole-dipole interactions * Hydrogen bonding

Question 31

How do London forces work?

Answer 31

* The electrons in molecules are constantly moving and at one time the electrons may be more towards one end of a molecule than another * This causes a temporary dipole * This temporary dipole can induce a dipole on neighbouring molecules

Question 32

When would London forces increase?

Answer 32

If the size of the molecule increases

Question 33

How do permanent dipole-dipole interactions work?

Answer 33

* Between polar molecules the opposite partial permanent charges attract * The whole molecule must however be polar and not just have polar bonds

Question 34

How does hydrogen bonding work?

Answer 34

Occurs when one molecule contains an electronegative atom (N, O or F) with a lone pair of electrons and another contains a hydrogen (attatched to a N, O or F)

Question 35

What is included in a hydrogen bond diagram?

Answer 35

* Partial charges * Lone pairs * 180° Bond angle around H * Dashed line showing Hydrogen bond

Question 36

How does hydrogen bonding affect water?

Answer 36

In a solid state water (ice) is less dense than liquid water as the water molecules are held further apart in an open lattice by hydrogen bonds.