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Chemistry > Chapter 6 - Shapes of Molecules and Intermolecular Forces > Flashcards

Chapter 6 - Shapes of Molecules and Intermolecular Forces Flashcards

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1
Q

What does molecular shape depend on?

A

Electron pairs around the central atom.

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2
Q

In what way do electron pairs interact?

A

They repel each other

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3
Q

Which type of pair repels the most?

A

Lone pairs

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4
Q

What is the order of pair repulsion, from weakest to strongest?

A

Bonding pair-bonding pair
Lone pair-bonding pair
Lone pair-lone pair

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5
Q

What is the way to predict a molecules shape?

A

Electron pair repulsion theory

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6
Q

What shape is given to a molecule with no lone pairs and 4 bonding pairs?

A

Tetrahedral

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7
Q

What is the bond angle in a tetrahedral molecule?

A

109.5 degrees

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8
Q

What shape is given to a molecule with 2 bonding pairs and 1 lone pair?

A

Non-linear

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9
Q

What shape is given to a molecule with 2 bonding pairs and 2 lone pairs?

A

Non-linear

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10
Q

What is the bond angle in a non-linear molecule with 2 lone pairs?

A

104.5 degrees

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11
Q

What shape is given to a molecule with 3 bonding pairs and 1 lone pair?

A

Pyramidal

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12
Q

What is the bond angle in a pyramidal molecule?

A

107 degrees

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13
Q

What shape name is given to a molecule with 2 bonding pairs around the central atom, with no lone pairs?

A

Linear

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14
Q

What is the bond angle in a linear molecule?

A

180 degrees

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15
Q

What shape name is given to a molecule with 3 bonding pairs around the central atom, with no lone pairs?

A

Trigonal planar

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16
Q

What is the bond angle in a trigonal planar molecule?

A

120 degrees

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17
Q

What shape is given to a molecule with 6 bonding pairs around the central atom, with no lone pairs?

A

Octahedral

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18
Q

What is the bond angle in an octahedral molecule?

A

90 degrees

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19
Q

What is electronegativity?

A

The attraction of a bonded atom for the pair of electrons in a covalent bond.

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20
Q

How is electronegativity measured?

A

Pauling scale

21
Q

What does a high Pauling value mean?

A

A higher electronegativity and therefore greater attraction for an electron pair in a covalent bond

22
Q

What makes a bond polar?

A

2 Atoms have different electronegativity values.

When the bonding electrons are pulled towards the more electronegative atom.

One atom becomes slightly positive charged, and one becomes slightly negative charged.

Forms polar covalent bond.

23
Q

What does a polar bond form?

A

A permanent dipole

24
Q

How is a dipole formed?

A

A difference in charge between the 2 atoms, caused by a shift in electron density in the bond.

25
Q

Are diatomic gases polar or non-polar? Why?

A

They are non-polar because the atoms have equal electronegativity so the electrons are equally attracted to both nuclei.

26
Q

What happens if the polar bonds are arranged symmetrically in a molecule?

A

The dipoles cancel each other out so the molecule has no overall dipole and is therefore non-polar.

27
Q

What is a dipole?

A

The separation of opposite charges within a molecule. Has the delta + and delta - signs.

28
Q

What happens if the polar bonds are arranged unsymmetrically in a molecule?

A

Uneven distribution of charge causing the molecule to have an overall dipole.

29
Q

What can the electronegativity predict about bonding?

A

Whether bonding is ionic or covalent.

30
Q

What can electronegativity tell us about ionic bonding?

A

In ionic bonding the difference in electronegativity is 1.8 or higher.

31
Q

What can electronegativity tell us about covalent bonding?

A

Atoms bonded covalently have zero difference in electronegativity. This is a pure covalent bond.

32
Q

What can electronegativity tell us about polar covalent bonding?

A

In polar covalent bonding the difference in electronegativity is between 0 and 1.8 and the molecule tends to be polar.

33
Q

What are intermolecular forces?

A

Weak interactions between dipoles of different molecules

34
Q

What is the order of intermolecular forces from weakest to strongest?

A

London forces
Permanent dipole-dipole interactions
Hydrogen bonding

35
Q

How are induced dipole-dipole interactions (London forces) formed?

A
  1. Movement of electrons produces a changing dipole in a molecule.
  2. At any instant, an instantaneous dipole exists, which induces a dipole on a neighbouring molecule.
  3. The induced dipole further induces dipoles on neighbouring molecules, which then attract one another.
36
Q

What is the effect of having more electrons in a molecule on London forces?

A

Larger instantaneous and induced dipoles
Greater induced dipole-dipole interactions

Causes stronger attractive forces between molecules

37
Q

What is the effect of stronger London forces?

A

Higher boiling point

38
Q

Why does boiling point increase when London forces are increased?

A

More electrons cause larger induced dipoles, so more energy is needed to overcome the intermolecular forces.

39
Q

What are permanent dipole-dipole interactions?

A

Intermolecular forces that occur between polar molecules that have an uneven distribution of charge.

40
Q

What is the effect of having permanent dipole-dipole interactions?

A

Higher boiling point

41
Q

Which molecules have London forces?

A

ALL molecules

42
Q

What is a simple molecular substance?

A

Substance with few atoms held together by covalent bonds like H2O, CO2, or Ne

43
Q

Why do simple molecular substances have low melting and boiling points?

A

Because they have weak intermolecular forces that are broken by energy present at low temperatures.

44
Q

Why don’t simple molecular substances usually dissolve in water?

A

There are little interactions between the molecules in the lattice and the water molecules.

45
Q

Why do simple molecular substances have poor electrical conductivity?

A

There are no mobile charged particles.

46
Q

How is hydrogen bonding formed?

A

A weak bond is polarised between a hydrogen atom of one molecule and a lone pair on a neighbouring molecules’ electronegative atom (e.g. oxygen, nitrogen, or fluorine)

47
Q

What effect does hydrogen bonding have on a molecule

A

Soluble in water

Higher boiling points

48
Q

Why does ice float on water?

A

Because hydrogen bonds hold water molecules apart in an open lattice structure, but when water freezes, the water molecules become further apart, causing ice to be less dense than water.

49
Q

What are 4 anomalous properties of water?

A

High boiling point
More dense in liquid form
Surface tension
High viscosity

Chemistry (20 decks)

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