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Chemistry > Shapes of molecules and intermolecular bonding > Flashcards

Shapes of molecules and intermolecular bonding Flashcards

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1
Q

What factors affect the shapes of molecules?

A
  • How many lone pairs/bonded pairs of electrons there are.
  • How many total electron pairs there are.
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2
Q

What is electron pair repulsion?

A

Electron pairs repel one another so they’re arranged as far apart as possible which minimises repulsion and holds the bonded atoms in a definite shape.

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3
Q

What does the line, dotted wedge and solid wedge represent?

A
  • Line = bond in the plane of the paper.
  • Dotted wedge = bond going into the plane of the paper.
  • Solid wedge = bond coming out of the plane of the paper.
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4
Q

Which molecules have a 3D shape?

A

Molecules with 4 or more areas of electron density.

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5
Q

What is the order of electron pair repulsion?

A
  • Lone pair/lone pair (strongest)
  • Lone pair/bonded pair
  • Bonded pair/bonded pair (weakest)
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6
Q

Why do lone pairs have a stronger repulsion than bonded pairs?

A

They’re closed to the nucleus and occupy more space than a bonded pair so they repel other electron pairs more strongly which pushes these pairs closer together, therefore decreasing the bond angle.

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7
Q

What shape and bond angle does CH4 have and why?

A
  • Tetrahedral shape
  • Bond angle 109.5
  • Because 4 areas of electron density
  • 4 bonded pairs and 0 lone pairs
  • BP/BP have lowest repulsion and repel equally to be as far apart as possible
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8
Q

What shape and bond angle does NH3 have and why?

A
  • Pyramidal shape
  • Bond angle of 107
  • Because 4 areas of electron density so tetrahedral derivative
  • Between 1 lone pair and 3 bonded pairs
  • Repel equally as the electrons want to be as far apart as possible due to BP/LP electron pair repulsion so bond angle decreases by 2.5 as 1 lone pair present
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9
Q

What shape and bond angle does H2O have and why?

A
  • Non-linear shape
  • Bond angle of 104.5
  • Because 4 areas of electron density so tetrahedral derivative
  • Between 2 lone pairs and 2 bonded pairs
  • Repel equally as the electrons want to be as far apart as possible due to BP/LP electron pair repulsion so bond angle decreases by 5 as 2 lone pairs present
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10
Q

What shape and bond angle does CO2 have and why?

A
  • Linear shape
  • Bond angle of 180
  • 2 areas of electron density
  • 4 bonded pairs and 0 lone pairs
  • BP/BP have lowest repulsion and repel equally to be as far apart as possible
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11
Q

What shape and bond angle does BF3 have and why?

A
  • Trigonal planar shape
  • Bond angle of 120
  • 3 areas of electron density
  • 3 bonded pairs and 0 lone pairs
  • BP/BP have lowest repulsion and repel equally to be as far apart as possible
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12
Q

What shape and bond angle does SO2 have and why?

A
  • Non-linear shape
  • Bond angle of 117.5
  • 3 areas of electron density so trigonal planar derivative
  • 1 lone pair and 2 bonded pairs so bond angle decreases by 2.5
  • Due to BP/LP electron pair repulsion, they repel equally to be as fair apart as possible
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13
Q

What shape and bond angle does PCl5 have and why?

A
  • Trigonal bipyramidal shape
  • Bond angles of 120 and 90
  • 5 areas of electron density
  • 5 bonded pairs and 0 lone pairs
  • BP/BP have lowest repulsion and repel equally to be as far apart as possible
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14
Q

What shape and bond angle does SF6 have and why?

A
  • Octahedral shape
  • Bond angles of 90
  • 6 areas of electron density
  • 6 bonded pairs and 0 lone pairs
  • (mirrored image)
  • BP/BP have lowest repulsion and repel equally to be as far apart as possible
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15
Q

What shape and bond angle does the NH4+ ion have?

A

Same shape and bond angle as CH4 and for the same reasons.

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16
Q

What is electronegativity?

A

The ability of an atom in a covalent bond to attract a shared pair of electrons.

17
Q

What factors affect electronegativity?

A
  • Size of atomic radius
  • Strength of nuclear charge
18
Q

How is electronegativity measured?

A

With Pauling values

19
Q

Why does electronegativity increase across a period?

A
  • Number of protons increase
  • Stronger nuclear charge
  • Electronegativity increases
20
Q

Why does electronegativity increase up a period?

A
  • Number of shells decrease
  • Distance to nucleus decreases
  • Stronger attraction to nucleus
  • Electronegativity increases
21
Q

How do we represent partial charges within bonds?

A

Delta - or delta +

22
Q

How can a covalent bond become ionic?

A

High electronegativity difference means electrons can be completely pulled onto one atom.

23
Q

What is polarity?

A

The uneven distribution of electrons caused by the difference of electronegativities.

24
Q

Why will a bond be non-polar?

A
  • The bonded atoms are the same
    OR
  • The bonded atoms have the same/similar electronegativity

so the bonded electron pair is shared equally between bonded atoms and will be shared roughly in the middle

25
Q

When will a bond be polar?

A
  • The bonded atoms are different
    OR
  • The bonded atoms have different electronegativity values
26
Q

What is a dipole?

A

The separation of opposite charges.

27
Q

What factors can cause a molecule to have a permanent dipole?

A
  • Molecular shape (symmetry)
  • Electronegativity
28
Q

Why may molecules with polar bonds have no overall dipole?

A

They would be symmetrical so the charges cancel out.

29
Q

Why does H2O have a permanent dipole? (Symmetry rule)

A
  • 2 lone pairs present so molecule is not symmetrical.
  • This means that dipoles (charges) do not cancel out.
  • Therefore the molecule has a permanent dipole meaning it’s polar.
30
Q

Why doesn’t CO2 have a permanent dipole? (Symmetry rule)

A
  • No lone pairs present so molecule is symmetrical.
  • This means the dipoles cancel out.
  • Therefore the molecule has no overall dipole so it’s non-polar.
31
Q

Why is PCl5H polar?

A
  • The surrounding atoms have different charges (H is delta positive and Cl is delta negative).
  • This means the molecule is not symmetrical.
  • Therefore the dipoles don’t cancel out so the molecule has a permanent dipole so it’s polar.
32
Q

Why are hydrocarbons never polar?

A

C and H have near identical electronegativity so C—H bonds are never polar.

Chemistry (2 decks)

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