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

Chapter 6 - Shapes of Molecules and Intermolecular Forces Flashcards

Shapes of molecules and ions, Electronegativity and polarity, Intermolecular forces and Hydrogen bonding.

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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 strongest to weakest?

A

Lone pair/lone pair
Lone pair/bonding pair
Bonding pair/bonding pair

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5
Q

What is the name of the way to predict a molecule’s shape?

A

Electron pair repulsion theory

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6
Q

What shape name is given to a molecule with no lone pairs but four bonded pais?

A

Tetrahedral

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7
Q

What is the bond angle in a tetrahedral molecule?

A

109.5

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8
Q

whats the shapes table?

A
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9
Q

what do dotted wedge, solid wedges and filled wedges stand for?

A
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10
Q

What shape name is given to a molecule with one lone pair and three bonding pairs?

A

pyramidal

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11
Q

What is the bond angle in a pyramidal molecule?

A

107

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12
Q

What shape name is given to a molecule with two lone pairs and one bonding pair?

A

Non-linear

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13
Q

What is the bond angle in a non-linear molecule?

A

104.5

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14
Q

What shape name is given to a molecule with 2 electron/bonded pairs around the central atom?

A

Linear

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15
Q

What is the bond angle in a linear molecule?

A

180

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16
Q

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

A

Trigonal planar

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17
Q

What is the bond angle in a trigonal planar molecule?

A

120

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18
Q

What shape name is given to a molecule with 5 electron pairs around the central atom?

A

Trigonal bipyramidal

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19
Q

What is the bond angle in a trigonal bipyramidal molecule?

A

There are actually two, 120 in one plane and 90 in the other plane.

20
Q

What shape name is given to a molecule with 6 electron pairs around the central atom?

A

Octahedral

21
Q

What is the bond angle in an octahedral molecule?

A

90

22
Q

What is electronegativity?

A

An atom’s ability to attract the electron pair in a covalent bond.

23
Q

How is electronegativity measured?

A

On the Pauling scale.

24
Q

What does a higher Pauling value mean?

A

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

25
Q

What makes a bond polar?

A

Two atoms with electronegativities differing by at least 0.5, the bonding electrons are pulled towards the more electronegative atom, making it polar.

26
Q

What does a polar bond form?

A

A permanent dipole

27
Q

how are the more and less electronegative elements shown?

A

𝛿− is more electronegative

𝛿+ is less electronegative

28
Q

How is a dipole formed?

A

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

29
Q

Are diatomic gases polar or non-polar, why?

A

Non-polar
Because the atoms have equal electronegativities and so the electrons are equally attracted to both nuclei.

30
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 non-polar.

31
Q

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

A

Uneven distribution of charge and the molecule will have an overall dipole.

32
Q

What can electronegativity be used to predict about bonding?

A

Whether it will be covalent or ionic bonding.

33
Q

What is the general strength of intermolecular forces?

A

Very weak

34
Q

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

A

Hydrogen bonding
Permanent dipole-dipole interactions
Induced dipole-dipole

35
Q

What are induced dipole-dipole forces?

A

Electrons in clouds can at one moment be unevenly distributed, creating a temporary dipole. This dipole induces another dipole on a neighbouring atom and the two are attracted to each other. The dipoles can then be brought about in a domino effect. Overall the atoms are attracted to one another.

36
Q

What is the effect of stronger induced dipole-dipole forces?

A

Higher boiling points

37
Q

Why do larger molecules have higher boiling point?

A

Larger molecules have larger electron clouds so stronger induced dipole-dipole forces.
Boiling point is overcoming the intermolecular forces so stronger ones means a higher boiling point.

38
Q

How are permanent dipole-dipole interactions labelled?

A

With charges of delta+ and delta- on the atoms.

39
Q

When can hydrogen bonding occur?

A

When hydrogen is covalently bonded to fluorine, nitrogen or oxygen.

40
Q

Why are hydrogen bonds brought about?

A

Hydrogen has a high charge densiy and F, N and O are very electronegative. The bond is so polarised that a weak bond forms between the hydrogen of one molecule and a lone pair on a neighbouring molecule’s F, N or O.

41
Q

What effect does hydrogen bonding have on a molecule?

A

Soluble in water.
Higher boiling and freezing points than molecules of a similar size that don’t form hydrogen bonds.

42
Q

What is an interesting property of ice caused by hydrogen bonding?

A

In ice, water molecules are held together in a lattice. When ice melts, hydrogen bonds are broken, so ice has more of these than water. As hydrogen bonds are long, this causes ice to be less dense than water.

43
Q

How do intermolecular forces explain simple covalent compounds having low melting and boiling points?

A

Weak intermolecular forces to overcome.

44
Q

How do intermolecular forces explain simple covalent compounds sometimes being soluble in water?

A

Water is also a polar molecule, hydrogen bonded molecules can form these with water molecules so are soluble.

45
Q

How do intermolecular forces explain simple covalent compounds not conducting electricity?

A

Overall covalent molecules are uncharged, permanent dipoles are not strong enough.

46
Q

what is the shape of molecules table?

A

OCR A-Level Chemistry A (36 decks)

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