CHM2045 Exam 3

How are atoms arranged in Lewis Structures (EN)

Least EN in the middle (never Hydrogen)

Hydrogen Octet Rule Exception

Okay with 2 electrons

Be Exception to octet rule

Only needs 4 electrons, but can have more

B exception to octet rule

Only needs 6 electrons, but can have more

Oxygen and Nitrogen exception to octet rule

Like to have 8 electrons, but can have 7

Period 3 and beyond exception to octet rule

Nonmetals in period 3 and beyond can have more than 8 electrons in the octent because they can use their d orbitals to make bonds

Formal charge formula

# of VE - # of electrons around the atom - # of bonds (count each line)

Where should the negative charge be in a lewis structure

On the most EN atom

What is resonance

All the ways a molecule can lok

What does A stand for in AX_mE_n

Central Atom

What does X stand for in AX_mE_n

How many atoms are bonded to the central atom (A)

What does E stand for in AX_mE_n

Number of lone pairs around the central atom

Shortcut to finding the shapes

1. Count VE

2. Subtract by highest multiple of 8 (divide by 8 to get the X)

3. Take the leftover electrons and divide by 2 (to get the E)

AX₂ Shape

Linear

Linear (AX₂) Ideal Bond Angle

180

Linear hybridization

sp

AX₃ shape

Trigonal Planar

Trigonal Planar (AX₃) ideal bond angle

120

Trigonal planar hybridization

sp²

AX₂E₁ shape

Bent

Bent (AX₂E₁) bond angle

<120 (117)

Bent (AX₂E₁) hybridization

sp²

AX₄ Shape

Tetrahedral

Tetrahedral (AX₄) Bond Angle

109.5

Tetrahedral (AX₄) hybridization

sp³

AX₃E₁ Shape

Trigonal Pyramidal

Trigonal Pyramidal (AX₃E₁) Bond Angle

<109.5 (107)

Trigonal Pyramidal (AX₃E₁ ) hybridization

sp³

AX₂E₂ Shape

Bent

Bent (AX₂E₂ ) Bond Angle

<109.5 (105)

Bent (AX₂E₂ ) Hybridization

sp³

Electron-pair delocalization

Double bonds are spread over the entire molecule

AX₅ Shape

Trigonal Bipyramidal

Trigonal Bipyramidal (AX₅ )Bond Angle

90, 120, and 180 bond angles

Trigonal Bipyramidal (AX₅) Hybridization

sp³d

AX₄E₁ Shape

See-Saw

See-Saw (AX₄E₁ ) Bond Angle

90, 117, and 180

See-Saw (AX₄E₁ )Hybridization

sp³d

T-Shaped Planar (AX₃E₂ ) Shape

T-Shaped Planar

T-Shaped Planar (AX₃E₂ ) Bond Angle

90, 180

T-Shaped Planar (AX₃E₂ ) Hybridization

sp³d

AX₂E₃ Shape

Linear

Linear (AX₂E₃ ) Bond Angle

180

Linear (AX₂E₃ ) Hybridization

sp³d

AX₆ Shape

Octahedral

Octahedral (AX₆) Bond Angle

90

Octahedral (AX₆) Hybridization

sp³d²

AX₆E₁ Shape

Square Pyramidal

Square Pyramidal (AX₆E₁ ) Bond Angle

90

Square Pyramidal (AX₆E₁ ) Hybridization

sp³d²

AX₄E₂ Shape

Square Planar

Square Planar (AX₄E₂ ) Bond Angle

90

Square Planar (AX₄E₂ ) Hybridization

sp³d²

What is the molecular geometry and formula of this molecule?

Linear: AX₂

What is the molecular geometry and formula of this molecule?

Linear: AX₂E₃

What is the molecular geometry and formula of this molecule?

Trigonal Planar: AX₃

What is the molecular geometry and formula of this molecule?

Bent: AX₂E₁

What is the molecular geometry and formula of this molecule?

AX₄

What is the molecular geometry and formula of this molecule?

Trigonal Pyramidal: AX₃E₁

What is the molecular geometry and formula of this molecule?

Trigonal Bipyramidal: AX₅

What is the molecular geometry and formula of this molecule?

See-Saw: AX₄E₁

What is the molecular geometry and formula of this molecule?

T-Shaped: AX₃E₂

What is the molecular geometry and formula of this molecule?

Octahedral: AX₆

What is the molecular geometry and formula of this molecule?

Square Pyramidal: AX₅E₁

What is the molecular geometry and formula of this molecule?

Square Planar: AX₄E₂

What is the electron geometry of: Linear

Linear

What is the electron geometry of: Trigonal Planar

Trigonal Planar

What is the electron geometry of: Bent

Trigonal Planar

What is the electron geometry of: Tetrahedral

Tetrahedral

What is the electron geometry of: Trigonal Pyramidal

Tetrahedral

What is the electron geometry of: Bent (AX₂E₂)

Tetrahedral

What is the electron geometry of: Trigonal Bipyramidal

Trigonal Bipyramidal

What is the electron geometry of: See-Saw

Trigonal Bipyramidal

What is the electron geometry of: T-Shaped Planar

Trigonal Bipyramidal

What is the electron geometry of: Linear (AX₂E₃)

Trigonal Bipyramidal

What is the electron geometry of: Octahedral

Octahedral

What is the electron geometry of: Square Pyramidal

Octahedral

What is polarity?

The uneven pulling/sharing of electrons around the central atom

What 2 dipole moment’s can polar molecules have?

Net dipole or non-zero dipole moment

What dipole moment can a nonpolar molecule have?

Zero dipole moment

Fir single center compounds, what can you use to determine if the molecule is polar?

1. Is the molecular geometry symmetrical

2. Are the outer atoms the same

Symmetrical Molecular Shapes

AX₂‒ Linear, AX₃‒ Trigonal Planar, AX₄‒ Tetrahedral, AX₅‒ Trigonal Bipyramidal ,

AX₂E₃‒ Linear, AX₆‒ Octahedral, AX₄E₂‒ Square Planar

Asymmetrical Molecular Shapes

AX₂E₁‒ Bent (V-shaped), AX₃E₁‒ Trigonal Pyramidal, AX₂E₂‒ Bent (Water Bent), AX₄E₁‒ See-Saw, AX₃E₂‒ T-shaped, AX₅E₁‒ Square Pyramidal

T/F: When any central atom has one lone pair, it is automatically polar.

True

How to determine the hybridization of a molecule?

Count the number of electron groups around the atom (count double and triple bonds as one)

What is a sigma bond?

Single localized bond in a compound (direct overlap)

For what 3 overlaps can a sigma bond be created?

Overlap of 2 s orbitals, 2 sp orbitals, or an sp orbital with an s orbital.

When is an sp orbital created?

When an s and a p orbital come together to delocalize the electron density around the central atom

Sigma v. Pi bonding in bond rotation

• Sigma bond: end-to-end bonding which allows bond rotation about the bond axis

• Pi bond: do not allow bond rotation

In a pi bonds, where do the 2 electrons move?

One e moves from the top lobe to the bottom lobe, and the other e moves from the bottom lobe to the top lobe continuously

Pi bonding gives rise to what kinds of isomers

Cis (same side) and trans (opposite side)

What is a cis isomer

When 2 of the same atoms are on the same side of the molecule

What is a trans isomer

When 2 atoms on the same side of the molecule are different. So the 2 atoms that are the same are on opposite sides of the molecule.

T/F: For a pi bond to occur, a sigma bond must occur first

True

Are sigma or pi bonds weaker? Why?

• Pi bonds are weaker

• Because the orbitals overlap less side to side (pi) than end to end (sigma)

What kinds of bonds does a single bond have?

1 sigma bond

What kinds of bonds does a double bond have?

1 sigma + 1 pi bonds

What kinds of bonds does a triple bond have?

1 sigma + 2 pi bonds

What is paramagnetic

There is at least one unpaired electron in the molecule

What is diamagnetic

All the electrons in the molecular are paired, there are no radicals