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Chemistry Module 2 > 6: Molecular Shapes, Polarity, Negativity, Intermolecular Forces, Hydrogen Bonds > Flashcards

6: Molecular Shapes, Polarity, Negativity, Intermolecular Forces, Hydrogen Bonds Flashcards

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1
Q

What does a solid wedge represent in a drawing?

A

That the shape is coming out of the plane of the paper.

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2
Q

What does a solid line represent in a drawing?

A

That the shape is in the plane of the paper

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3
Q

What does a dotted wedge represent in a drawing?

A

That the shape is going into the plane of the paper

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4
Q

What is the name of the shape of a molecule with 2 areas of electron density?

A

Linear

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5
Q

What is the bond angle for a molecule with 2 areas of electron density?

A

180°

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6
Q

What is the name of the shape of a molecule with 3 areas of electron density?

A

Trigonal planar

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7
Q

What is the bond angle for a molecule with 3 areas of electron density?

A

120°

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8
Q

What is the name of the shape of a molecule with 6 areas of electron density?

A

Octahedral

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9
Q

What is the bond angle for a molecule with 6 areas of electron density?

A

90°

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10
Q

What is the name of the shape of a molecule with 5 areas of electron density?

A

Trigonal bipyramidal

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11
Q

What is the bond angle for a molecule with 5 areas of electron density?

A

Two angles, 90° and 120°

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12
Q

What is the name of the shape of a molecule with 4 areas of electron density (4 bonded pairs, no lone pairs)?

A

Tetrahedral

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13
Q

What is the bond angle for a molecule with 4 areas of electron density?

A

109.5°

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14
Q

What is the name of the shape of a molecule with 4 areas of electron density (3 bonded pairs, 1 lone pair)?

A

Pyramidal

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15
Q

What is the bond angle for a molecule with 4 areas of electron density (3 bonded pairs, 1 lone pair)?

A

107°

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16
Q

What is the name of the shape of a molecule with 4 areas of electron density (2 bonded pairs, 2 lone pairs)?

A

Non-linear

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17
Q

What is the bond angle for a molecule with 4 areas of electron density (2 bonded pairs, 2 lone pairs)?

A

104.5°

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18
Q

Why do electron pairs repel eachother?

A

Because they have the same charge

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19
Q

What do the electron pairs surrounding a central atom determine?

A

The shape of the molecule or ion.

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20
Q

What does the arrangement of electron pairs minimise?

A

Repulsion, and holds the bonded atoms in a definite shape

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21
Q

What makes a bonded pair different to a lone pair of electrons?

A

-Lone pairs are slightly closer to the central atom
-Lone pairs occupy more space than a bonded pair
-Lone pairs repel more strongly than a bonded pair

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22
Q

How do lone pairs decrease the bond angle?

A

Because lone pairs repel more strongly than a bonded pair, they repel bonded pairs slightly closer together, which decreases the angle between the bonded pairs of electrons

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23
Q

How much is the bond angle reduced by for each lone pair?

A

2.5°

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24
Q

What should you state when answering questions about molecular shapes?

A

-Molecular shape
-Bond angle
-Areas of electron density
-Number of lone pairs
-Identify the central atom
-Recognise lone pairs repel more than bonded pairs, and electron pairs repel equally.

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25
Q

What is electronegativity?

A

The ability of an atom to attract a pair of electrons in its own covalent bonds.

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26
Q

Why can atoms attract electrons in a bond by different strengths?

A

Because atoms have different numbers of protons and different atomic radii.

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27
Q

What is the Pauling Scale?

A

A scale used to represent the relative electronegativities of an atom. The higher the value, the higher the electronegativity.

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28
Q

What scale is used to represent the relative electronegativities of an atom?

A

The Pauling Scale

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29
Q

What makes a bond polar?

A

If the distribution of charge across the bond is asymmetrical (i.e one atom has a higher electronegativity than the other)

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30
Q

What does the δ (Delta) sign mean?

A

Partially / a little bit

31
Q

What is the electronegativity difference in a covalent bond?

A

0

32
Q

What is the electronegativity difference in a Polar Covalent bond?

A

≥0 ≤1.8

33
Q

What is the electronegativity difference in an ionic bond?

A

> 1.8

34
Q

What can electronegativity values be used to estimate?

A

The type of bonding.

35
Q

When is a molecule polar?

A

When there is an asymmetrical distribution of charge across the entire molecule, so the dipoles don’t cancel out.

36
Q

What is a dipole?

A

Charge separation across a bond with one atom having a δ+ charge and another having a δ- charge.

37
Q

How can you obtain a permanent dipole?

A

The molecule has to be polar.

38
Q

What is a permanent dipole-dipole interaction?

A

Where permanent dipoles attract one another / Electrostatic forces of attraction between two permanently polar molecules

39
Q

What is a polar covalent bond?

A

A shared pair of electrons, where the electron pair is not shared equally between the two bonded atoms.

40
Q

Can ionic compounds be dissolved by polar molecules?

A

Yes.

41
Q

Describe how water molecules break down an NaCl ionic lattice.

A

-Water molecules attract Na+ AND Cl- ions
-The ionic lattice breaks down as it dissolves
-In the resulting solution, water molecules surround the Na+ and Cl- ions.

42
Q

What are the three main categories that intermolecular forces fall into?

A

-Induced dipole-dipole interactions (LONDON DISPERSION FORCES)
-Permanent dipole-dipole interactions
-Hydrogen bonding.

43
Q

What is an alternative name for London Dispersion Forces?

A

Induced dipole-dipole interactions. (Sometimes called Van der Waals forces)

44
Q

What types of molecules show London Dispersion Forces?

A

All molecules, but only in non-polar molecules is it the strongest force.

45
Q

Explain London Dispersion Forces.

A

-Random electron movement in a molecule creates an instantaneous dipole, where charge is momentarily asymmetrically distributed.
-The dipole is instantaneous because the charge is instantaneously distributed asymmetrically
-This charge affects the electrons in a neighbouring molecule, inducing a dipole. This affects all other molecules in the substance.

46
Q

The more electrons in each molecule…

A

-The larger the instantanous and induced dipoles
-The greater the induced dipole-dipole interactions
-The stronger the attractive forces between molecules

47
Q

How does a larger number of electrons increase the boiling point?

A

-Larger number of electrons mean larger induced dipoles
-More energy is needed to overcome the intermolecular forces.

48
Q

What does immiscible mean?

A

When two liquids don’t mix, but instead form 2 separate layers

49
Q

What does miscible mean?

A

When two liquids mix together to form a single uniform liquid

50
Q

Do non-polar solutes dissolve in non-polar solvents?

A

Yes

51
Q

Why do non-polar solutes dissolve in non-polar solvents?

A

Because the London Dispersion Forces of attraction form between the non-polar simple molecular solute and the non-polar simple-molecular solvent.

52
Q

Why do polar molecules have higher boiling points?

A

Because extra energy is needed to break the additional dipole-dipole interactions between the molecules

53
Q

What types of dipole interactions/forces do molecules WITHOUT dipoles display?

A

London Dispersion Forces

54
Q

What types of dipole interactions/forces do molecules WITH dipoles display?

A

London Dispersion Forces and Permanent Dipole-Dipole Interactions

55
Q

What is the name of the structure that simple molecules form in a solid form?

A

A simple molecular lattice.

56
Q

What holds the molecules in place in a simple molecular lattice?

A

Weak intermolecular forces.

57
Q

What bonds the atoms within a simple molecular lattice together?

A

Strong covalent bonds.

58
Q

What does the solubility of a polar simple molecular substance depend on?

A

The strength of the dipole.

59
Q

Are simple molecules conductive of electricity?

A

No

60
Q

Why aren’t simple molecules conductive of electricity?

A

Because there are no mobile charged particles, so there is nothing to complete an electrical circuit.

61
Q

What is hydrogen bonding?

A

A specific, stronger example of permanent dipole-dipole interactions.

62
Q

What has to be there for hydrogen bonding to occur?

A

-A small highly electronegative atom with a lone pair of electrons to interact with the H atom (N, O or F)
-A hydrogen atom bonded to N, O or F (so partially positive)

63
Q

What is the criteria for drawing hydrogen bonds?

A

-Draw all lone pairs
-Draw all partial charges
-Draw hydrogen bond from the H atom to the lone pair
-All 3 atoms in H bonds have to be at an 180 degree angle

64
Q

What does a hydrogen bond act between?

A

A lone pair of electrons on an electronegative atom in one molecule, and a hydrogen atom in a different molecule

65
Q

What is the strongest type intermolecular attraction?

A

Hydrogen bond

66
Q

What symbolises a hydrogen bond in a bond drawing?

A

A dashed line

67
Q

What are the anomalous properties of water that are provided by hydrogen bonding?

A

-Its solid form is less dense than water
-Water has a high melting and boiling point

68
Q

Why is ice less dense than water?

A

-The water molecules in ice are further apart than in water
-Each water molecule can form 4 hydrogen bonds. These bonds extend outwards, holding water molecules slightly apart and forming an open tetrahedral lattice full of holes. The holes in the open lattice structure decrease the density of water.

69
Q

What gives water its high melting and boiling point?

A

-Water has London dispersion forces between molecules
-Hydrogen bonds are extra forces over and above the London forces.
-A large amount of energy is needed to break the hydrogen bonds in water, so water has much higher melting and boiling points than expected.

70
Q

Describe what happens to the hydrogen bonds when ice melts

A

-The rigid arrangement of hydrogen bonds in the ice is broken

71
Q

Describe what happens to the hydrogen bonds when water evaporates

A

The hydrogen bonds break completely

72
Q

What contributes to water having a relatively high surface tension and viscosity?

A

Extra intermolecular bonding from hydrogen bonding.

73
Q

Are ionic compounds polar?

A

Yes, and they dissolve in polar solvents.

Chemistry Module 2 (7 decks)

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