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Chem 150 > Module 5: Exam 3 > Flashcards

Module 5: Exam 3 Flashcards

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1
Q

2 electron groups, 0 lone pairs

A

linear

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2
Q

3 electron groups, 0 lone pairs

A

trigonal planar

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3
Q

3 electron groups, 1 lone pair

A

bent

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4
Q

4 electron groups, 0 lone pairs

A

tetrahedral

2 atoms in opposite planes

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5
Q

4 electron groups, 1 lone pair

A

trigonal pyramidal

2 atoms in opposite planes

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6
Q

4 electron groups, 2 lone pairs

A

bent

atoms are not in opposite planes, technically the lone pairs are, but we do not show this

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7
Q

5 electron groups, 0 lone pairs

A

trigonal bypyramidal

2 atoms in opposite planes

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8
Q

6 electron groups, 0 lone pairs

A

octahedral

4 atoms in opposite planes

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9
Q

Linear ideal angle

A

180

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10
Q

Trigonal planar ideal angle

A

120

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11
Q

Tetrahedral ideal angle

A

109.5

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12
Q

Trigonal bypyramidal ideal angle

A

Distance between equatorial: 120
Distance between axial and equatorial: 90

*drawing helps understand this

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13
Q

What are molecular geometries based on?

A

Electron electron repulsion in ALL electron groups (bonded and lone pairs)

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14
Q

Octahedral ideal angle

A

90

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15
Q

Why do lone pairs squish bonds together?

A

Because they only are attracted to 1 nucleus, instead of 2, this gives them less force of attraction

Therefore, they have more space to spread out and repel other domains

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16
Q

What repels more single bonds or double bonds?

A

Double bonds since they have greater electron density

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17
Q

When is it okay for a 1st period element to have a 2- or 2+ formal charge?

A

When it is in a resonance structure

When just drawing Lewis structures this is NOT allowed

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18
Q

Do resonance structures truly exist?

A

No

They are just representations

All bonds are the same length between the same atoms surrounding a central atom

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19
Q

Why is hybridization and resonance structures favored/

A

They are often more stable than an individual structure that does not exist as a resonance molecule

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20
Q

What defined electron group geometry?

A

The number of areas of electron density surrounding the central atom

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21
Q

How do hybrids add up?

A

If there is 2 unhybridized orbitals, they will come together to form 2 hybridized orbitals

This is due to the law of conservation of energy

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22
Q

sp3

A

commonly used with 4 electron domains (tetrahedral)

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23
Q

sp2

A

commonly used with 3 electron domains (trigonal planar)

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24
Q

Where does resonance happen?

A

pi-bonds

25
Q

When there is a leftover p-orbital, where is it?

A

remember that p-orbitals can be in 3 planes. and if you are using two of them for a sp2 orbital, then the leftover is in the z-plane

this makes it perpendicular

26
Q

Orientation of pi-bonds

A

perpendicular

because they are the leftover p-orbitals

27
Q

What constitutes an electron domain?

A

a lone pair = 1

a single bond = 1

a double bond = 1

a triple bond = 1

28
Q

Why do electron domains like to be as far apart as possible?

A

Since electrons repel eachother, want to be far apart to minimize force of repulsion and lower energy

29
Q

Valence bond theory

A

atoms share electrons when an atomic orbital on one atom overlaps with an atomic orbital on the other

30
Q

What holds electrons together in covalent bond?

A

mutual attraction to the nuclei

31
Q

What happens when 2 single bonded orbitals overlap?

A

they both become doubly occuppied

32
Q

Which theory explains why a bond forms?

A

valence bond theory

33
Q

When will a covalent bond form?

A

the potential energy of the resulting molecule is lower than the potential energy of 2 separate atoms

34
Q

What happens energetically when bonds are formed?

A

energy is released

force of attraction increasing, energy dropping

35
Q

Hybridization

A

the mixing of atomic orbitals

an extension of valence bond theory for when valence bond theory fails

36
Q

What does an sp orbital look like?

A

large lobe and small lobe

50% s-characteristics
50% p-characteristics

37
Q

sp

A

commonly used with 2 electron domains (linear)

38
Q

What do we use hybrid orbitals for?

A

not to predict geometries, that is vsepr, rather we use them to EXPLAIN geometries that we already know

39
Q

sp3d2

A

commonly used with 6 electron domains (octahedral)

40
Q

Unique about the 3rd period and beyond in terms of hybridization

A

electrons can be promoted to the d-orbital

octets can be overloaded

41
Q

3 steps to evaluate the importance of resonance structures

A
  1. determine if all the atoms have a complete octet. full octet>not full
  2. count # of atoms with formal charges. less formal charges=greater importance
  3. if same # of atoms with formal charges, see where they lie. more electronegative atoms want the negative charge
42
Q

What happens to ionization energy as you go across p table?

A

increases

43
Q

What happens to ionization energy as you go down p table?

A

decreases

44
Q

What happens to atomic radius as you go accross?

A

decreases

45
Q

What happens to atomic radius as you go down?

A

increases

46
Q

Delocalized bond

A

pi-bond is spread out over the entire molecule

double bonds are not in one location because each bond surrounding a central atom connected to the same other atom, has the same length

therefore, bonds are not in one spot. they are constantly changing

47
Q

Are pi-bonds stronger than sigma?

A

No. Sigma bonds are stronger because they involve the most direct overlap

Pi bonds are more of a cloud over bonds

48
Q

Why is a double bond not twice the strength of a single bond?

A

Because it is not two sigma bonds

it is a sigma bond and a pi bond. the pi bond is not as strong.

49
Q

What is stronger delocalized bond or localized?

A

delocalized

50
Q

Why are delocalized bonds stronger?

A

they increase stability through resonance

there is a loss of internal energy which makes more stable

since electrons repel eachother, by distributing them further apart over multiple bonds, energy is reduced

51
Q

Why is cyclic geometry less stable in a triangle?

A

Forces electrons into 60º angles which makes them very close

HOWEVER, it depends the shape. An aromatic ring like benzene it very stable because angle is still 120º

52
Q

Which is more stable sp2 or sp3? Why?

A

sp2 because it has a greater percentage of s-character

sigma bonds are strong because they are direct overlap of orbitals

53
Q

What is a possible reason the bond angle might not be predicted by VSEPR?

A

it could be due to a resonance structure that gives a geometry that is better predicted by vsepr

54
Q

What does VSEPR stand for?

A

valence shell electron pair repulsion

55
Q

Who invented vsepr?

A

Gillespie and Nyholm

56
Q

What are the limitations of vsepr?

A

fails to take into account differences in isoelectric species

fails for transition metals

57
Q

Formula for bond order

A

number of bonds / number of atoms sharing them

58
Q

Relationship between bond order and bond length

A

as bond order increases, bond length decreases

Chem 150 (10 decks)

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