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Chemistry (Tara) > Shapes of molecules > Flashcards

Shapes of molecules Flashcards

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1
Q

What is used to work out the shapes of molecules?

A

VSEPR theory

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2
Q

What VSEPR Theory stand for?

A 
Valence
Shell
Electron
Pair
Repulsion
Theory
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3
Q

What does the VSEPR theory state?

A

That the outermost pairs of electrons in a molecule try to get as far away from each other as possible so as to minimise the repulsion between these electrons in the outermost shell.

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4
Q

What does the VSEPR theory arrangement allow?

A

For a stable molecule.

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5
Q

What determines the shape of the molecules?

A

The number and type of groups of electrons.

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6
Q

What is the best arrangement of a given number of electrons pairs?

A

The one that minimises the repulsions among them.

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7
Q

What are bonding pairs?

A

These are pairs of electrons in the outermost shell that are taking part in bonding. These types of electrons are shared between atoms.

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8
Q

What are lone pairs?

A

These are pairs of electrons in the outermost shell that do not take part in bonding. These electrons are not shared. The lone pairs of the central atom are the ones that affect the shape.

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9
Q

How do bonding pairs repel each other?

A

Equally

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10
Q

What has a greater repelling effect bonding pairs or lone pairs?

A

Lone pairs

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11
Q

What do lone pairs have a greater repelling effect then bonding pairs?

A

As they are found closer to the nucleus of the central atom as they do not have to be shared between atoms.

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12
Q

Greatest repulsion

A

lone pair - lone pair

lone pair - bond pair

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13
Q

Least repulsion

A

bond pair - bond pair

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14
Q

What is the only possible shape for a molecule with two atoms?

A

Linear - bond angle 180°

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15
Q

Shapes of molecules consisting of 3 atoms (AB₂) Type 1

A

Linear
(A) - central atom in group 2
(B) - a monovalent atom (i.e H, F, Cl, Br, I)

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16
Q

Shapes of molecules consisting of 3 atoms (AB₂) Type 2

A

V-shaped
(A) - central atom in group 6
(B) - a monovalent atom (i.e H, F, Cl, Br, I)

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17
Q

What is a double or triple bond counted as when predicting shapes?

A

One bonding pair

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18
Q

Example of shapes of molecules consisting of 3 atoms -type 1 BeH₂, name central atom

A

Be

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19
Q

Example of shapes of molecules consisting of 3 atoms -type 1 BeH₂, state amount of electrons in outer shell of central atom.

A

2

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20
Q

Example of shapes of molecules consisting of 3 atoms -type 1 BeH₂, state what Be is bonded to.

A

2 atoms of H

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21
Q

Example of shapes of molecules consisting of 3 atoms -type 1 BeH₂ how many electrons does each H want?

A

1 each

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22
Q

Example of shapes of molecules consisting of 3 atoms -type 1 BeH₂, how many electrons of the central atom, Be will take part in bonding?

A

All, 2

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23
Q

Example of shapes of molecules consisting of 3 atoms- type 1 BeH₂, how many bonding pairs?

A

2

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24
Q

Example of shapes of molecules consisting of 3 atoms -type 1 BeH₂, how many lone pairs?

A

0

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25
Q

Example of shapes of molecules consisting of 3 atoms -type 1 BeH₂, what is the shape?

A

Linear

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26
Q

Example of shapes of molecules consisting of 3 atoms -type 1, BeH₂, what is the bond angle?

A

180°

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27
Q

Give 3 examples of linear molecules (excluding BeH₂)

A

BeCl₂
CO₂
CS₂

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28
Q

Example of shapes of molecules consisting of 3 atoms -type 2, H₂O, what is the central atom?

A

O

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29
Q

Example of shapes of molecules consisting of 3 atoms -type 2, H₂O, how many electrons in outer shell of central atom?

A

6

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30
Q

Example of shapes of molecules consisting of 3 atoms -type 2, H₂O, what is O bonded to?

A

2 atoms of H

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31
Q

Example of shapes of molecules consisting of 3 atoms -type 2, H₂O, how many electrons does each H want?

A

1 each

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32
Q

Example of shapes of molecules consisting of 3 atoms -type 2, H₂O, how many electrons of the central atom, O will take place in bonding?

A

2 out of 6

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33
Q

Example of shapes of molecules consisting of 3 atoms -type 2, H₂O, what is the number of bonding pairs?

A

2

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34
Q

Example of shapes of molecules consisting of 3 atoms -type 2, H₂O, what is the number of lone pairs?

A

2

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35
Q

Example of shapes of molecules consisting of 3 atoms -type 2, H₂O, what is the shape of the molecule?

A

V-shaped (or distorted tetrahedral)

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36
Q

Example of shapes of molecules consisting of 3 atoms -type 2, H₂O, what is the bond angle?

A

104.5°

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37
Q

Give 3 examples of v-shaped molecules (excluding H₂O)

A

H₂S
SCl₂
Cl₂O

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38
Q

BeH₂ ‘drawing’

A

H —— Be ——- H

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39
Q

Shapes of molecules consisting of 4 atoms (AB₃) Type 1

A

(A) - central atom in group 3
(B) - a monovalent atom (i.e. H, F, Cl, Br, I)
Triangular planar

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40
Q

Examples of shapes of molecules consisting of 4 atoms - Type 1, BF₃, name the central atom.

A

B

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41
Q

Examples of shapes of molecules consisting of 4 atoms - Type 1, BF₃, how many electrons are in outer shell of central atom?

A

3

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42
Q

Examples of shapes of molecules consisting of 4 atoms - Type 1, BF₃, what is the central atom (B) bonded to?

A

3 atoms of flourine

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43
Q

Examples of shapes of molecules consisting of 4 atoms - Type 1, BF₃, how many electrons does each F want?

A

1 each

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44
Q

Examples of shapes of molecules consisting of 4 atoms - Type 1, BF₃, how many electrons of the central atom, B will take part in bonding?

A

All, 3

45
Q

Examples of shapes of molecules consisting of 4 atoms - Type 1, BF₃, what is the number of bonding pairs?

A

3

46
Q

Examples of shapes of molecules consisting of 4 atoms - Type 1, BF₃, what is the number of lone pairs?

A

0

47
Q

Examples of shapes of molecules consisting of 4 atoms - Type 1, BF₃, what is the shape of the molecule?

A

Triangular planar

48
Q

Examples of shapes of molecules consisting of 4 atoms - Type 1, BF₃, what is the bond angle?

A

120°

49
Q

Give 3 examples of triangular planar molecules (excluding BF₃)

A

BH₃
AlCl₃
HCHO

50
Q

Examples of molecules consisting of 4 atoms (AB₃) -type 2

A

Pyramidal
(A) - central atom in group 5
(B) - a monovalent atom (i.e. H, F, Cl, Br, I)

51
Q

Give 5 examples of monovalent atoms

A

H, F, Cl, Br, I

52
Q

Examples of shapes of molecules consisting of 4 atoms - Type 2, NH₃, what is the central atom?

A

N

53
Q

Examples of shapes of molecules consisting of 4 atoms - Type 2, NH₃, how many electrons are in the outer shell of the central atom?

A

5

54
Q

Examples of shapes of molecules consisting of 4 atoms - Type 2, NH₃, what is the central atom (N) bonded to?

A

3 atoms of H

55
Q

Examples of shapes of molecules consisting of 4 atoms - Type 2, NH₃, how many electrons does each H want?

A

1 each

56
Q

Examples of shapes of molecules consisting of 4 atoms - Type 2, NH₃, how many electrons of the central atom, will take part in bonding?

A

3 out of 5

57
Q

Examples of shapes of molecules consisting of 4 atoms - Type 2, NH₃, what is the number of bonding pairs?

A

3

58
Q

Examples of shapes of molecules consisting of 4 atoms - Type 2, NH₃, what is the number of lone pairs?

A

1

59
Q

Examples of shapes of molecules consisting of 4 atoms - Type 2, NH₃, what is the shape of the molecule?

A

Pyramidal

60
Q

Examples of shapes of molecules consisting of 4 atoms - Type 2, NH₃, what is the bond angle?

A

107°

61
Q

Give two examples of molecules with a pyramidal shape. (excluding NH₃)

A

PH₃

AsH₃

62
Q

Bond angle in PH₃

A

94°

63
Q

Bond angle in AsH₃

A

92°

64
Q

Why is the bond angle in PH₃ 94° and the bond angle in AsH₃ 92°? (L.C)

A

Because the increasing atomic radius of the central atom and the decreasing electronegativity of the central atom. The shared pairs of electrons are further away from the central atom and further away from each other. Thus there is a smaller force of repulsion between them and the bonds become closer.

65
Q

Shapes of molecules containing 5 atoms (AB₄)

A

Tetrahedral
(A) - central atom is in group 4
(B)….. ask

66
Q

Example of shapes of molecules containing 5 atoms (AB₄), CH₄, what is the central atom?

A

C

67
Q

Example of shapes of molecules containing 5 atoms (AB₄), CH₄, how many electrons are in the outer shell of central atom?

A

4

68
Q

Example of shapes of molecules containing 5 atoms (AB₄), CH₄, what is the central atom (C) bonded to?

A

4 atoms of H

69
Q

Example of shapes of molecules containing 5 atoms (AB₄), CH₄, how many electrons does each H want?

A

1 each

70
Q

Example of shapes of molecules containing 5 atoms (AB₄), CH₄, how many electrons of the central atom, C will take part in bonding?

A

4 out of 4

71
Q

Example of shapes of molecules containing 5 atoms (AB₄), CH₄, what is the number of bonding pairs?

A

4

72
Q

Example of shapes of molecules containing 5 atoms (AB₄), CH₄, what is the number of lone pairs?

A

0

73
Q

Example of shapes of molecules containing 5 atoms (AB₄), CH₄, what is the shape of the molecule?

A

Tetrahedral

74
Q

Example of shapes of molecules containing 5 atoms (AB₄), CH₄, what is the bond angle?

A

109°

75
Q

Give two examples of tetrahedral molecules (excluding CH₄)

A

SiH₄

GeH₄

76
Q

What must be done to work out the shapes of complex ions?

A

You follow the same method, however you must either add or subtract electrons from the central atom depending whether the ion is negative or positive.

77
Q

What does the negative sign indicate in NH₂- ?

A

An extra electron in the central atom.

78
Q

Example of complex ions, NH₂-, what is the central atom?

A

N

79
Q

Example of complex ions, NH₂-, how many electrons are in the outer shell of the central atom.

A

5 in atom + 1 extra = 6

80
Q

Example of complex ions, NH₂-, what is the central atom (N) bonded to?

A

2 atoms of H

81
Q

Example of complex ions, NH₂-, how many electrons does each H want?

A

1 each

82
Q

Example of complex ions, NH₂-, how many electrons of the central atom, N will take part in bonding?

A

2 out of 6

83
Q

Example of complex ions, NH₂-, what is the number of bonding pairs?

A

2

84
Q

Example of complex ions, NH₂-, what is the number of lone pairs?

A

2

85
Q

Example of complex ions, NH₂-, what is the shape of the molecule?

A

V-shaped

86
Q

Example of complex ions, NH₂-, what is the bond angle?

A

104.5°

87
Q

Two atoms in molecule

A

Has to be linear

88
Q

Three atoms in a molecule

A

Is either linear (no lone pairs) or V-shaped (has lone pairs).

89
Q

Four atoms in molecule

A

Is either trigonal planar (no lone pairs) or pyramidal (has lone pairs).

90
Q

Five atoms in a molecule

A

Is tetrahedral

91
Q

State and account for the shape of a tetrachloromethane molecule. (L.C)

A
  • Tetrahedral

- Four pairs electron and no lone pairs

92
Q

Use electron pair repulsion theory to predict the shape of a molecule of boron trifluoride. (L.C)

A

Trigonal planar

93
Q

Predict the shape of the arsine (AsH₃) molecule (L.C)

A

Pyramidal

94
Q

Account for the difference in the shapes of the boron triflouide (BF₃) molecule and the ammonia (NH₃) molecule. (L.C)

A

Boron has three bond pairs of electrons

Nitrogen has three bond pairs and one lone pair of electrons

95
Q

Ammonia (NH₃) and silane (SiH₄) are small molecules, each of which has four electron pairs in the valence shell of the central atom. Account for the difference in bond angle between the two molecules, 107.3 degrees in ammonia and 109.5 degrees in silane. (L.C)

A
  • Lone pair of electrons has greater repelling power than a bond pair of electrons.
  • Ammonia has three bond pairs (one lone pair) whereas silane has four bond pairs (no lone pair).
96
Q

Give the shape and the corresponding bond angle for a molecule of formula QX₄ where Q is an element from group 4 of the periodic table. (L.C)

A
  • Tetrahedral

- 109°28’

97
Q

What are two possible shapes of molecules of general formula QX₂ ? (L.C)

A
  • Linear

- V-shaped

98
Q

Account for the difference in bond angle between water (104.5) and methane (109.5) (L.C)

A
  • Lone pair(s) of electrons in water

- Have greater repelling power (repulsion)

99
Q

Would you expect the hydrogen sulphide molecule to be linear or non-linear in shape? Justify your answer. (L.C)

A
  • Non-linear

- There are non-bonding/lone pairs

100
Q

What are the two possible shapes for molecule of general formula AB₂? (L.C)

A
  • Linear

- V-shaped

101
Q

Account for the difference in the shapes of the ammonia (NH₃) and boron trifluoride (BF₃) molecules. (L.C)

A
  • NH₃ has three bond pairs and one lone pair

- BF₃ has three bond pairs (DRAWN ALSO)

102
Q

Are the abbreviations b.p and l.p acceptable in exam?

A

NO!!

103
Q

Which is the following molecules has a shape that is different from the other three? BF₃, AsH₃, HCHO, AlCl₃. State the shape of the molecule you have chosen (L.C)

A

n

104
Q

Write the formula of the simplest chloride you would expect the element of atomic number 33 to form. (L.C)

A

n

105
Q

State two possible shapes for molecules of general formula OX₂, where Q is a divalent element and X is an atom of chlorine, bromine or iodine. (L.C)

A

n

106
Q

Define electronegativity (L.C)

A

The relative power of attraction an atom of an element has for the shared pair of electrons in a covalent bond.

107
Q

Define covalent bond (L.C)

A

Covalent bonding occurs when electrons are shared between atoms. Atoms share to attain eight elements (usually). This type of bonding normally occurs between non-metal atoms.

108
Q

State the valence shell electron pair repulsion theory (L.C). (check for 6th)

A

This theory states that the outermost pairs of electrons in a molecules try to get as far away from each other as possible so as to minimise the repulsion between these electrons in the outermost shell.

Chemistry (Tara) (50 decks)

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