Organic Chemistry: Unit 1

What are valence electrons?

Electrons in an atom’s outermost shell.

What does the octet rule state?

Most atoms are most stable when they have 8 electrons in their valence shell.

How many electrons does hydrogen want?

2 electrons.

How many bonds does neutral hydrogen usually form?

1 bond.

How many bonds does neutral carbon usually form?

4 bonds.

How many bonds and lone pairs does neutral nitrogen usually have?

3 bonds and 1 lone pair.

How many bonds and lone pairs does neutral oxygen usually have?

2 bonds and 2 lone pairs.

How many bonds and lone pairs do F, Cl, Br, and I usually have?

1 bond and 3 lone pairs.

What is electronegativity?

An atom’s ability to pull electrons toward itself.

How does electronegativity change across the periodic table?

It generally increases going up and to the right.

What is the most electronegative element?

Fluorine.

What three things should a Lewis structure show?

Bonds, lone pairs, and formal charges.

What is the first step for drawing a Lewis structure?

Count all valence electrons.

How do you usually choose the central atom?

Choose the least electronegative atom.

What atom should generally never be the central atom?

Hydrogen.

After choosing the central atom, what is the next step?

Connect atoms using single bonds.

What should you do after connecting atoms with single bonds?

Give the outer atoms full octets.

Where do remaining electrons go after the outer atoms have octets?

On the central atom.

What should you do if the central atom still lacks an octet?

Form double or triple bonds.

What should be checked at the end of a Lewis structure?

Formal charges.

What is the formal charge equation?

Formal charge = valence electrons − nonbonding electrons − number of bonds

How many electrons does each bond represent when checking an octet?

2 electrons.

How many electrons are in one lone pair?

2 electrons.

Why do atoms form bonds or transfer electrons?

To reach a more stable electron configuration, often a full octet.

In a line-angle structure, what does every line end represent?

A carbon atom.

In a line-angle structure, what does every corner represent?

A carbon atom.

Are hydrogens attached to carbon normally drawn in line structures?

No.

How do you determine how many hydrogens are attached to a carbon in a line structure?

Assume the carbon has enough hydrogens to give it 4 total bonds.

Which atoms should be written explicitly in line structures?

Atoms such as O, N, Cl, and Br.

Do double and triple bonds need to be shown in line structures?

Yes.

What does DBE stand for?

Degree of unsaturation.

What does DBE tell you?

How many rings and/or π bonds are present in a molecule.

What is the DBE equation?

DBE = [2(C) + 2 + N − H − X] / 2
where X = number of halogens.

Which elements are ignored when calculating DBE?

Oxygen and sulfur.

Which atoms count as halogens in the DBE equation?

F, Cl, Br, and I.

What does a DBE of 0 mean?

No rings or multiple bonds.

What does a DBE of 1 mean?

One ring or one double bond.

What could a DBE of 2 represent?

Two double bonds, two rings, one triple bond, or another combination totaling 2.

What must atoms to the right of carbon generally have?

A complete octet.

What must always be shown when present?

Formal charges.

Can second-row elements such as B, C, N, O, and F exceed 8 electrons?

No.

Can elements in rows below the second row sometimes exceed an octet?

Yes.

What should bond angles in a drawing reflect?

The approximate actual molecular geometry.

How should a linear arrangement be drawn?

It should look linear.

What usually happens if an atom has a different number of bonds from its normal neutral bonding pattern?

A formal charge is introduced.

Why is DBE useful before drawing a structure?

It tells you how many rings or multiple bonds must be included.

What geometry must a triple bond have?

Linear.

What does molecular orbital theory explain?

Bonding by combining atomic orbitals from different atoms into molecular orbitals.

When two atomic orbitals combine, what two molecular orbitals form?

One bonding orbital and one antibonding orbital.

What creates a bonding molecular orbital?

In-phase overlap of atomic orbitals.

What does “in-phase” mean?

The overlapping lobes have the same sign or phase.

What type of overlap occurs in a bonding orbital?

Constructive overlap.

Where is electron density increased in a bonding molecular orbital?

Between the nuclei.

How does a bonding orbital affect energy?

It lowers the energy and stabilizes the bond.

What creates an antibonding molecular orbital?

Out-of-phase overlap.

What does “out-of-phase” mean?

Opposite signs/phases overlap.

What type of overlap occurs in an antibonding orbital?

Destructive overlap.

What forms between the nuclei in an antibonding orbital?

A node.

How does an antibonding orbital compare energetically to the original atomic orbitals?

It is higher in energy.

If two atomic orbitals combine, how many molecular orbitals must result?

Two.

Is the number of orbitals conserved when atomic orbitals combine?

Yes.

What do + and − signs on orbital lobes represent?

The phase/sign of the wave function, not electrical charge.

How is a sigma (σ) bond formed?

By head-on orbital overlap.

Where is electron density located in a sigma bond?

Along the line connecting the two nuclei.

What type of bond are most single bonds?

Sigma bonds.

How is a pi (π) bond formed?

By side-by-side overlap of p orbitals.

Where is electron density located in a pi bond?

Above and below the bond axis.

What bonds make up a double bond?

1 σ bond + 1 π bond.

What bonds make up a triple bond?

1 σ bond + 2 π bonds.

In a bonding π orbital, what phases overlap?

The same phases.

Is there a node between the atoms in a bonding π orbital?

No central node between the atoms.

In an antibonding π orbital, what phases overlap?

Opposite phases.

What is an easy way to recognize an antibonding orbital?

Look for a node between the nuclei.

How many electrons can one molecular orbital hold?

2 electrons.

Where do electrons go first in an MO diagram?

Into the lowest-energy available orbital.

What happens when electrons are removed from a bonding orbital?

The bond is weakened or broken.

What happens when electrons are added to an antibonding orbital?

The bond is weakened or can be broken.

What must an electron have to enter an antibonding orbital?

The appropriate energy and symmetry.

What orbital does every bond have in addition to its bonding orbital?

A corresponding antibonding orbital.

What does VSEPR stand for?

Valence Shell Electron Pair Repulsion.

What does VSEPR help predict?

Molecular geometry and hybridization.

What does VSEPR try to maximize?

Space between electron groups.

What are hybrid orbitals?

Orbitals created by mixing atomic orbitals to produce the geometry needed for bonding.

What hybridization corresponds to 2 electron domains?

sp.

What geometry corresponds to sp hybridization?

Linear.

What is the bond angle for sp hybridization?

180°.

What hybridization corresponds to 3 electron domains?

sp².

What geometry corresponds to sp² hybridization?

Trigonal planar.

What is the bond angle for sp² hybridization?

120°.

What hybridization corresponds to 4 electron domains?

sp³.

What geometry corresponds to sp³ hybridization?

Tetrahedral.

What is the ideal bond angle for sp³ hybridization?

109.5°.

What type of bonds do hybrid orbitals make?

Sigma bonds.

What is the first bond between any two atoms?

A sigma bond.

What type of bonds are additional bonds between the same two atoms?

Pi bonds.

What are alkanes?

Molecules containing carbon–carbon and carbon–hydrogen single bonds.

What suffix is used for alkanes?

-ane

What determines the prefix of an alkane name?

The number of carbons in the parent chain.

What prefix represents 1 carbon?

meth-

What prefix represents 2 carbons?

eth-