Bonding

Question 1

What is the bond angle, name of shape and how many electron pairs does this molecule have?

Answer 1

• Linear
• 180˚ Bond Angles
• 2 Electron Pairs

Question 2

What is the bond angle, name of shape and how many electron pairs does this molecule have?

Answer 2

• Trigonal Planar
• 120˚ Bond Angles
• 3 Electron Pairs

Question 3

What is the bond angle, name of shape and how many electron pairs does this molecule have?

Answer 3

• Tetrahedral
• 109.5˚ Bond Angles
• 4 Electron Pairs

Question 4

What is the bond angle, name of shape and how many electron pairs does this molecule have?

Answer 4

• Trigonal Bipyramid(ial)
• 120˚ and 90˚ Bond Angles
• 5 Electron Pairs

Question 5

What is the bond angle, name of shape and how many electron pairs does this molecule have?

Answer 5

• Octahedral
• 90˚ Bond Angles
• 6 Electron Pairs

Question 6

What does a thick black wedge show?

Answer 6

The atom “coming out” of the paper.

Question 7

What does a dashed wedge show?

Answer 7

The atom “going into” the paper.

Question 8

Define Lone Pair.

Answer 8

A lone pair is a pair of electrons that are not involved in bonding.

Question 9

What bond angles does water have, what do we call that type of molecule (3) and how many lone pairs does a molecule with this bond angle have?

Answer 9

• 104.5˚ Bond Angles
• We call this:
  
  • Bent
  • Angular
  • V-shaped
• This has 2 lone pairs.

Question 10

Why does water have lone pairs on the oxygen atom rather than on the hydrogen atoms?

Answer 10

Oxygen is more electronegative than hydrogen, so the lone pairs go closer to the oxygen than the hydrogen.

Question 11

Why does water take the shape of a “bent” molecule?

Answer 11

The lone pairs come closer to the oxygen than the bonding pair of electrons, so the lone pairs repel more. In addition, the lone pairs aren’t shared out between atoms, so they are more concentrated areas of charge. Both of these factors contribute to making the hydrogens repel and the molecule “bending”.

Question 12

Give the repulsion hierachy for lone pairs and bonding pairs.

Answer 12

Lone pair/lone pair > Lone pair/bonding pair > Bonding pair/bonding pair.

Question 13

Give the bond angles, name of the shape it forms and an example of a molecule with four atoms and one lone pair.

Answer 13

• Pyramidal Shape
• 107˚ Bond Angles
• Ammonia (NH₃)

Question 14

Explain what forms van der Waals intermolecular forces of attraction.

Answer 14

Electrons form a “cloud” around the atom, which causes temporary δ+ and δ- inducements in opposite ends of the atom as it moves. When non-polar molecules get very close to each other, they induce temporary dipole-dipole inducements. These are polar inducements, therefore the attraction is electrostatic.

Question 15

What causes an atom to have stronger van der Waals forces of attraction?

Answer 15

• Being larger (so it has more electrons)
• Being in molecules (noble gases can still have van der Waals forces of attraction, but they are very weak; take helium which has a very low melting point (4˚K), it still has van der Waals but very few)

Question 16

What sort of molecules have van der Waals forces of attraction?

Answer 16

None polar molecules - those with an overall electronegativity of zero (e.g. I₂) or that are symmetrical (e.g. CH₄). Metals cannot have van der Waals forces of attraction due to delocalised electrons.

Question 17

What sort of attraction takes place between hydrogen chloride (HCl) molecules?

Answer 17

Permanent dipole-dipole interactions. No van der Waals.

Question 18

How does a permanent dipole-dipole force take place?

Answer 18

Between two polar molecules, the negative end of one molecule attracts the positive end of another molecule.

Question 19

Give the 2 factors that influence the strength of permanent dipole-dipole forces.

Answer 19

1. More polar (greater difference in electronegativity) makes a stronger dipole force;
2. Distance between the atoms/molecules also changes the dipole force (closer = stronger).

Question 20

Between what elements can hydrogen bonding occur?

Answer 20

Between Hydrogen and the lone pairs of Oxygen, Nitrogen or Fluorine.

Question 21

What is the strongest intermolecular force of attraction?

Answer 21

Hydrogen bonding.

Question 22

Can more than one intermolecular force of attraction take place at any one time between molecules?

Answer 22

Yes

Question 23

What is responsible for making water a liquid at room temperature?

Answer 23

Hydrogen bonding.

Question 24

What properties do hydrogen-bonded molecules have?

Answer 24

Viscous molecules with high boiling points (most being different from the general trend in their group).

Question 25

Give 3 examples of substances that can participate in hydrogen bonding.

Answer 25

• Water
• DNA
• Kevlar

Question 26

What is a co-ordinate (or dative covalent) bond?

Answer 26

A co-ordinate bond is a covalent bond where the bonding pair of electrons both come from the same atom.

Question 27

Give an example of a co-ordinate-bonded molecule.

Answer 27

NH₄⁺

Question 28

How do we denote a coordinate bond on a diagram?

Answer 28

The co-ordinate bond is shown by an arrow; the arrow points from the atom donating the lone pair to the atom accepting it.

Question 29

Instead of an H⁺ ion, what are we usually talking about when we talk about acids? Give the reason and a property of the other substance.

Answer 29

A hydroxinium ion, as hydrogen is simply a proton and is far too reactive to exist on its own. H₃O⁺ ions have a co-ordinate bond.