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Chem 1: Elements of Life > EL5: Shapes of Molecules > Flashcards

EL5: Shapes of Molecules Flashcards

(67 cards)

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1
Q

What does VSEPR stand for?

A

Valence Shell Electron Pair Repulsion Theory

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2
Q

Define VSEPR

A

The shape adopted by a simple molecule/ion to keep its repulsive forces at a minimum

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3
Q

How are molecules held together?

A

Covalent bonds

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4
Q

Why does each covalent bond repel the other?

A

Covalent bonds consist of pairs of electrons

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5
Q

Why do bonds push each other as far apart as possible?

A

To reduce the repulsive forces between their pairs of electrons

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6
Q

Why are bonds equally spaced?

A

Because repulsions between each bond are equal

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7
Q

What bond angle does a linear molecule have?

A

180 degrees

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8
Q

How many bond pairs does a linear molecule have?

A

2

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9
Q

Define a linear molecule

A

An atom/ion where two groups of electrons surround its centre

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10
Q

Give 3 examples of linear molecules

A
  • BeCl2
  • CO2
  • Ethyne
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11
Q

What bond angle does a trigonal planar/planar triangular molecule have?

A

120 degrees

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12
Q

How many bond pairs does a trigonal planar/planar triangular molecule have?

A

3

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13
Q

Define a trigonal planar/planar triangular molecule

A

An atom/ion where three groups of electrons surround its centre

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14
Q

Give three examples of trigonal planar/planar triangular molecules

A
  • Ethene
  • Methanol
  • BF3
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15
Q

What bond angle does a tetrahedral molecule have?

A

109.5 degrees

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16
Q

How many bond pairs does a tetrahedral molecule have?

A

4

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17
Q

Define a tetrahedral molecule

A

An atom or ion where four groups of electrons surround its centre

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18
Q

Give three examples of tetrahedral molecules

A
  • Methane
  • Ethane
  • Ammonium ion
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19
Q

What bond angles does a trigonal bipyramidal molecule have?

A

120 or 90 degrees (depending on the position in the molecule)

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20
Q

How many bond pairs does a trigonal bipyramidal molecule have?

A

5

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21
Q

Define a trigonal bipyramidal molecule

A

An atom/ion where five groups of electrons surround its centre

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22
Q

Give an example of a trigonal bipyramidal molecule

A

PF5

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23
Q

What bond angle does an octahedral molecule have?

A

90 degrees

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24
Q

How many bond pairs does an octahedral molecule have?

A

6

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25
Define an octahedral molecule
An atom/ion where six groups of electrons surround its centre
26
Give one less common example of an octahedral molecule
- SF6
27
Where are octahedral shapes usually found?
- In the shapes of complexes of metal ions with six ligands e.g Ni(NH3)6
28
Why are shapes sometimes slightly distorted away from their regular shapes in a molecule/ion?
If the molecule/ion has lone pairs on the central atom, extra repulsion caused by them results in distortion of the regular shape
29
Order the following from the causing the most repulsion to causing the least - Lone Pair to Bond Pair - Bond Pair to Bond Pair - Lone Pair to Lone Pair
Lone Pair to Lone Pair > Lone Pair to Bond Pair > Bond Pair to Bond Pair
30
How much does each lone pair reduce the bond angle by?
2.5 degrees
31
How many groups of electrons does a trigonal based pyramid molecule have?
4
32
What types of electron groups does a trigonal based pyramid molecule have?
- 3x single covalent bonds | - 1x lone pair of electrons
33
What bond angle does the trigonal based pyramid shaped molecule have?
107 degrees
34
What is the main example of a trigonal based pyramid molecular shape?
Ammonia
35
What causes ammonia to have a trigonal based pyramid molecular shape?
The lone pair in nitrogen repulses the hydrogen-nitrogen bond pairs, pushing them closer together
36
What shape is the trigonal based pyramid and bent/v-shaped shape based on?
Tetrahedral shape
37
How many groups of electrons does a bent/v-shaped molecule have?
4
38
What types of groups of electrons does a bent/v-shaped molecule have?
- 2x single covalent bonds | - 2x lone pair of electrons
39
What is the main example of a bent/v-shaped molecule?
Water
40
Why does water have a bent/v-shaped molecular shape?
The lone pair to lone pair repulsions of the two lone pairs in the oxygen pushes the Oxygen-Hydrogen bonds together
41
Define "covalent bond"
A very strong attraction between the bonding pair of electrons and the nucleui of the atoms involved in the bond
42
Define a "bonding pair"
An electron pair that forms a bond in a covalent structure
43
Define a "lone pair"
Pairs of electrons uninvolved in the bonding of a covalent structure
44
Define "bond"
The electrostatic attraction between atoms/ions in a structure
45
Define "electrostatic attraction"
A strong electrical force of attraction
46
What does bonding involve?
The sharing or transferring of electrons in the highest occupied electron shells
47
What do all substances "want" to become?
Ions with a full outer shell
48
Why do substances want a full outer shell?
As this is the most energetically stable arrangement
49
What group of elements have the most energetically stable arrangements naturally and why?
The noble gases, by the balancing of electrical forces in the atom due to the equal number of protons and electrons
50
Define "electronegativity"
The ability of an atom to attract the electron pair in a covalent bond to itself
51
Explain why a non polar bond is non polar.
A bond with similar atoms - so they have the same electronegativity so they will both pull on the electrons to the same extent and be equally shared
52
Explain why a polar bond is polar.
- A bond with different atoms - so they have different electronegativity - Therefore one will pull the electron pair closer to its end - It will be slightly more negative than the overall bond (δ−) - The other atom will be slightly less negative - more positive (δ+) - A dipole is formed and the bond is said to be polar
53
How does the electronegativity of the atoms in a polar bond relate to its polarity?
The greater the difference in electronegativity between the two atoms in the bond, the greater the bond's polarity
54
What is the Pauling Scale?
A scale for measuring electronegativity
55
What is a non-polar covalent bond between?
The same/very similar non metals e.g Cl2
56
What is a polar covalent bond between?
Different non-metals e.g H2O
57
Order the following in order of increasing polarisation: - Polar covalent - Metallic - Non - polar covalent - Ionic
- Non - polar covalent - Polar covalent - Ionic - Metallic
58
What is a dot and cross diagram used to show?
The bonding in covalent structures and represent the way they bond together
59
What do line diagrams show?
They show a pair of electrons being shared between two atoms for every line in the diagram
60
Define a "co-ordinative dative bond"
Both electrons of a shared pair are provided by one species (element)
61
Describe the bonding of a CO molecule
- Involves a triple bond - 2 of the pairs of electrons are formed by the carbon and oxygen atoms each contributing one electron to the pair as in a normal covalent bond - Both electrons in the third pair come from the oxygen atom
62
Describe the bonding of an ammonium ion (NH4+)
- The lone pair N is used to share with the hydrogen ion which needs two electrons to fill its outer shell - The N now has a positive charge as its now sharing rather than owning two electrons
63
Describe the bonding in boron trifluoride - ammonia (NH3BF3)
- Boron has an incomplete shell in BF3 and can accept a share of a pair of electrons donated by ammonia - The B becomes negative as it now shares a pair of electrons that it didn't have before
64
What are the electrical properties of covalent substances and why?
They do not conduct electricity because they have no mobile ions/electrons
65
Are covalent substances soluble in water and why?
- No they tend to be more so in organic solvents | - The polar water molecules are more attracted to each other than the molecular substance and so do not react with it
66
Why do covalent bonds have a low melting point?
Because they have weak intermolecular forces which means little energy is needed to separate molecules from each other
67
Why does CH4 have a lower melting point than C2H6?
Because the molecule has a smaller surface area

Chem 1: Elements of Life (5 decks)

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