2.7 VSEPR and Hybridization

The valence shell electron-pair repulsion (VSEPR) theory predicts the:

geometries of molecules and polyatomic ions

The shape, or geometry, of a molecule is determined by:

lone pairs or bonds on the central atom of a molecule

Why is the shape or geometry of a molecule determined by the lone pairs or bonds on the central atom of a molecule?

these areas of electron density or “charge clouds” will minimize electron – electron repulsions by positioning themselves as far apart as possible.

Lone pairs of electrons repel more/less than bonds

more

Lone pairs of electrons tend to expand/compress the angle between bonding atoms.

compress

Lone pairs and bonds are called:

charge clouds

What should you do first when determining molecular geometry?

Draw lewis dot structure

Double and triple bonds should be counted as how many charge clouds?

one

Single electrons are counted as how many charge clouds?

one

How to determine geometry shape if there are more than 1 central atoms?

determine the geometric shape of each central atom individually

Name, hybridization, and bond angle for molecule with 2 sigma bonds:

linear, sp, 180 degrees

Diagram for molecule with 2 sigma bonds

Name, hybridization, and bond angle for molecule with 3 sigma bonds:

Trigonal planar, sp², 120 degrees

Diagram for molecule with 3 sigma bonds

Name, hybridization, and bond angle for molecule with 2 sigma bonds and 1 unshared electron pair

Bent, sp², <120 degrees

Diagram for molecule with 2 sigma bonds and 1 unshared electron pair

Name, hybridization, and bond angle for molecule with 4 sigma bonds

Tetrahedral, sp³, 109.5 degrees

Diagram for molecule with 4 sigma bonds:

Name, hybridization, and bond angle for molecule with 3 sigma bonds and 1 unshared electron pair

Trigonal pyramidal, sp³, <109.5 degrees

Diagram for molecule with 3 sigma bonds and 1 unshared electron pair

Name, hybridization, and bond angle for molecule with 2 sigma bonds and 2 unshared electron pair

Bent, sp³, <109.5 degrees

Diagram for molecule with 2 sigma bonds and 2 unshared electron pair

Name, hybridization, and bond angle for molecule with 5 sigma bonds and 0 unshared electron pairs

Trigonal bipyramidal, sp³d, 90 degrees and 120 degrees

Diagram for molecule with 5 sigma bonds and 0 unshared electron pair

Name, hybridization, and bond angle for molecule with 4 sigma bonds and 1 unshared electron pairs

See-saw, sp³d, 90 degrees and 120 degrees

Diagram for molecule with 4 sigma bonds and 1 unshared electron pairs

Name, hybridization, and bond angle for molecule with 3 sigma bonds and 2 unshared electron pairs

T-shaped, sp³d, 90 degrees

Diagram for molecule with 3 sigma bonds and 2 unshared electron pairs

Name, hybridization, and bond angle for molecule with 2 sigma bonds and 3 unshared electron pairs

Linear, sp³d, 180 degrees

Diagram for molecule with 2 sigma bonds and 3 unshared electron pairs

Name, hybridization, and bond angle for molecule with 6 sigma bonds and 0 unshared electron pairs

Octahedral, sp³d², 90 degrees

Diagram for molecule with 6 sigma bonds and 0 unshared electron pairs

Name, hybridization, and bond angle for molecule with 5 sigma bonds and 1 unshared electron pairs

Square pyramidal, sp³d², 90 degrees

Diagram for molecule with 5 sigma bonds and 1 unshared electron pairs

Name, hybridization, and bond angle for molecule with 4 sigma bonds and 2 unshared electron pairs

Square planar, sp³d², 90 degrees

Diagram for molecule with 4 sigma bonds and 2 unshared electron pairs

To explain molecular geometries, we assume that:

the atomic orbitals on an atom mix to form hybrid orbitals.

The shape of a hybrid orbital is a:

mix of the shapes of the original atomic orbitals such as s (spherical) and p (dumbbell).

The total number of atomic orbitals on an atom remains constant / changes

remains constant

the number of hybrid orbitals on an atom equals the:

number of atomic orbitals that are mixed

Why is the number of hybrid orbitals on an atom equal to the number of atomic orbitals that are mixed?

The total number of atomic orbitals on an atom remains constant

In methane, (CH4), the 2s and three 2p orbitals of carbon mix to form:

four sp3 hybrid orbitals

Relationship between the sum of the superscripts on the hybrid orbitals and the number of electron clouds around the central atom:

equal

The sum of the superscripts in sp3 equals:

4

Overlapping orbitals from a single bond are known as:

sigma bonds (σ)

Sigma bonds are ______ bonds

very strong

Double and triple bonds are formed from:

unhybridized p orbitals

Double and triple bonds are called:

pi bonds(π)

A double bond contains ______ sigma (σ) and ______ pi (π) bond(s).

one, one

A triple bond contains ______ sigma (σ) and ______ pi (π) bond(s).

one, two

The presence of pi bonds means that bonds are:

unable to rotate

The presence of pi bonds leads to:

geometric isomers

Why does the presence of pi bonds lead to geometric isomers?

The presence of pi bonds means that bonds are unable to rotate

Molecules have the same atoms but have different arrangements and are not superimposable.

Geometric isomer

As the number of bonds between two atoms increases, the bond increases/decreases in strength and energy

increases

As the number of bonds between two atoms increases, the bond increases/decreases in length

decreases

Pi bonds pull atoms closer together / push atoms farther apart

pull atoms closer together

The number of bonds between two atoms

Bond order

When the bond order increases, the bond length increases/decreases

decreases

When the bond order increases, the bond energy increases/decreases

increases

Bond order of single bond:

1

Bond order of double bond:

2

Bond order of triple bond:

3

For a molecule that exhibits resonance, we see that the bonds that have resonance are experimentally determined to:

be the same length

In an ozone molecule, is the single bond or the double bond longer?

Same

Bond lengths of single and double bonds in ozone molecules

Both halfway between a single and double bond length

Bond order of single and double bonds in ozone molecules

1.5

How to calculate bond order of molecules that exhibit resonance?

number of bonds shared divided by number of shared bonds between two atoms (could be any bond type)

When electrons are shared in a covalent bond, the shared electrons spend more time around the:

more electronegative element in the bond

Shared electrons spending more time around the more electronegative element in the bond gives it a:

partial negative charge (ẟ-)

Shared electrons spending more time around the more electronegative element in the bond gives the less electronegative element a:

slightly positive charge (ẟ+)

Covalent bonds form _____ molecules

polar

Why do covalent bonds form polar molecules?

Shared electrons form more time around more electronegative element, giving the more electronegative element a partial negative charge and the less electronegative element a slightly positive charge

In a polar molecule, the arrow in the diagram points to the:

More electronegative element

Is HCl a polar molecule?

Yes

Why is HCl a polar molecule?

It has a dipole moment that isn’t cancelled out

If a molecule is polar, it has a:

dipole moment

How to know if a molecule is polar:

know if the bonds are polar and the overall shape of the molecule

Drawing in the arrows pointing to the more electronegative element in equal and opposite directions demonstrates that the molecule has:

polar bonds but is overall a nonpolar molecule.

If the molecular geometry is bent, drawing the arrows indicates that the dipoles:

do not cancel

Why is water a polar molecule?

It has a bent shaped so dipoles do not cancel