Bonding

Question 1

What is an ionic bond?

Answer 1

Electrons are transferred from one atom to another; resulting ions are held together by electrostatic interactions

Question 2

What is a covalent bond?

Answer 2

Electrons are shared between atoms

Question 3

What do quantum numbers describe?

Answer 3

The energy level, shape, orientation, and spin of an electron within an atom

Question 4

What do the first three quantum numbers, n, l, ml describe?

Answer 4

The size, shape, number and orientation of atomic orbitals an element possesses

Question 5

What does the fourth quantum number, ms describe?

Answer 5

Spin

Question 6

Name all quantum numbers in order, what the number describes, its organizational levels, and possible values:

Answer 6

1. n, principal quantum number, size, shell, 1 to infinity (although MCAT will only test up to 7)
2. l, azimuthal quantum number, shape, subshell, 0-(n-1)
3. ml, magnetic quantum number, orientation, orbital, -l-+l
4. ms, spin quantum number, spin, (n/a), +/- 1/2

Question 7

What happens when two atomic orbitals combine?

Answer 7

They form molecular orbitals

Question 8

What kind of molecular orbital forms when the signs of the wave functions atomic orbitals are the same?

Answer 8

Bonding orbital

Question 9

Is a bonding orbital more or less stable, higher or lower-energy?

Answer 9

Lower-energy, more stable

Question 10

What kind of molecular orbital forms when the signs of the wave functions of atomic orbitals are different?

Answer 10

Antibonding orbital

Question 11

Is an antibonding orbital more or less stable, higher or lower-energy?

Answer 11

Higher-energy, less stable

Question 12

When a molecular orbital is formed by head-to-head or tail-to-tail overlap, what is the resulting bond?

Answer 12

A sigma bond; single bond

Question 13

All sigma bonds are what kinds of bonds?

Answer 13

Single bonds

Question 14

When two p-orbitals line up in a parallel fashion and their electron clouds overlap, what is the resulting bond?

Answer 14

A pi bond

Question 15

What does a double bond consist of?

Answer 15

A pi bond on top of an existing sigma bond

Question 16

What does a triple bond consist of?

Answer 16

Two pi bonds and a sigma bond

Question 17

Do double and triple bonds allow free rotation of atoms around the bond axis?

Answer 17

No, these bonds hinder movement, and essentially lock atoms into their positions

Question 18

What contributes to overall bond length?

Answer 18

The kind of bond, triple bonds have a shorter bond length than double bonds and double bonds have a shorter bond length than single bonds

Question 19

Do shorter or longer bonds hold atoms more closely together? Which require more energy to break?

Answer 19

Shorter bonds hold atoms more closely together, shorter bonds require more energy to break

Question 20

Are double bonds stronger than single bonds?

Answer 20

Yes

Question 21

Are individual pi bonds stronger than single, sigma bonds?

Answer 21

No

Question 22

Why is it possible to break only one bond in a double bond, allowing isomers to be interconverted between conformations?

Answer 22

This is because independent pi bonds are weaker than single, sigma bonds. In the case of a double bond, where a pi bond overlaps a single bond, breaking the double bond allows atoms to freely rotate around the bond axis, and thus be interconverted between isomer conformations.

Question 23

Does it require more energy to break a pi bond in a double bond or a single bond?

Answer 23

It requires more energy to break a sigma, single bond than to break a pi bond.

Question 24

Rank the following orbitals in order of decreasing strength.
1. Triple bonds
2. Double bonds
3. Pi bonds
4. Sigma (single bonds)

Answer 24

Triple bond > double bond > single (sigma) bond > pi bond

Question 25

What differences would be observed in a molecule containing a double bond compared to the same molecule containing only single bonds?

Answer 25

The bond lengths of a molecule containing a double bond would be shorter. The molecule would also be more rigid in comparison to the same molecule containing only single bonds.

Question 26

What does hybridization of orbitals do?

Answer 26

Hybridization is a way of making all bonds to a central atom equivalent to each other

Question 27

How are hybrid orbitals formed?

Answer 27

By mixing different types of orbitals

Question 28

What kind of geometry does carbon prefer?

Answer 28

Tetrahedral geometry

Question 29

What kind of hybridized orbitals does tetrahedral geometry utilize?

Answer 29

sp^3, where one s- and three p- orbitals mix

Question 30

What kind of hybridization is seen in alkenes?

Answer 30

sp^2

Question 31

How do you determine the amount of s character a certain hybrid orbital has?

Answer 31

See what percentage of the hybrid orbital is an s-orbital and what other percentage is a p-orbital

Question 32

For sp^3 orbitals, how much s character does the orbital have?

Answer 32

25% s character, 75% p character

Question 33

For sp^2 orbitals, how much s character does the orbital have?

Answer 33

33% s character, 67% p character

Question 34

For sp orbitals, how much s character does the orbital have?

Answer 34

50% s character, 50% p character

Question 35

What kind of geometry do molecules with sp orbitals exhibit?

Answer 35

linear

Question 36

What does conjugation of bonds refer to?

Answer 36

Conjugation requires alternating single and multiple bonds that allows delocalization of electrons across the entire system, improving overall molecular stability

Question 37

What are resonance structures?

Answer 37

Resonance structures differ in their placement of electrons in hybridized p-orbitals and require bond conjugation to delocalize electrons in a molecule

Question 38

How does the true electron density of a compound relate to its resonance structure?

Answer 38

The true electron density is a weighted average of the resonance structures of a given compound, favoring the most stable structures

Question 39

What is bond strength determined by?

Answer 39

The degree of orbital overlap; the greater the overlap, the greater the bond strength

Question 40

Why is a pi bond weaker than a single bond?

Answer 40

There is significantly less overlap between the unhybridized p-orbitals of a pi bond than between the s-orbitals or hybrid orbitals of a single bond