Chapter 1: A Review of General Chemistry

Question 1

What is the difference between organic and inorganic compounds?

Answer 1

Organic compounds contain carbon atoms, while inorganic compounds generally lack carbon atoms.

Question 2

What are constitutional isomers?

Answer 2

Constitutional isomers share the same molecular formula but have different connectivity of atoms and different physical properties.

Question 3

When do formal charges occur?

Answer 3

A formal charge occurs when atoms do not exhibit the appropriate number of valence electrons; formal charges must be drawn in Lewis structures.

Question 4

What are the three classifications of bonds?

Answer 4

1. Covalent
2. Polar covalent
3. Ionic

Question 5

What is induction and where does it occur?

Answer 5

Polar covalent bonds exhibit induction, causing the formation of partial positive charges and partial negative charges.

Question 6

What is the purpose of electrostatic potential maps?

Answer 6

Electrostatic potential maps present a visual illustration of partial charges.

Question 7

Describe bond-line structures.

Answer 7

In bond-line structures, carbon atoms and most hydrogen atoms are not drawn.

Question 8

How does quantum mechanics describe electrons?

Answer 8

In terms of their wavelike properties.

Question 9

What does the wave equation describe?

Answer 9

A wave equation describes the total energy of an electron when in the vicinity of a proton.

Question 10

What are wavefunctions?

Answer 10

Solutions to wave equations (ψ). The wavefunction squared (ψ2) represents the probability of finding an electron in a particular location.

Question 11

How are atomic orbitals represented visually?

Answer 11

By generating three-dimensional plots of ψ2.

Question 12

What do nodes indicate about the value of ψ?

Answer 12

Nodes indicate that ψ is zero.

Question 13

Where is electron density found in an atom?

Answer 13

Within occupied orbitals.

Question 14

Electrons fill orbitals according to which three principles?

Answer 14

1. The Aufbau principle
2. The Pauli exclusion principle
3. Hund’s rule

Question 15

What are degenerate orbitals?

Answer 15

Orbitals with the same energy level.

Question 16

What is the basic premise of valence bond theory?

Answer 16

VBT treats every bond as the sharing of electron density between two atoms as a result of the constructive interference of their atomic orbitals.

Question 17

When are sigma bonds formed?

Answer 17

Sigma bonds are formed when the electron density is located primarily on the bond axis.

Question 18

What is the basic premise of molecular orbital theory?

Answer 18

MOT uses a mathematical method called the linear combination of atomic orbitals (LCAO) to form molecular orbitals. Each molecular orbital is associated with the entire molecule, rather than just two atoms.

Question 19

How are bonding molecular orbitals formed?

Answer 19

The bonding MO of molecular hydrogen results from constructive interference between its two atomic orbitals.

Question 20

How are antibonding molecular orbitals formed?

Answer 20

The antibonding MO of molecular hydrogen results from destructive interference between its two atomic orbitals.

Question 21

What is the difference between an atomic and molecular orbital?

Answer 21

An atomic orbital is a region of space associated with an individual atom, while a molecular orbital is associated with an entire molecule.

Question 22

What is HOMO?

Answer 22

The highest occupied molecular orbital.

Question 23

What is LUMO?

Answer 23

The lowest unoccupied molecular orbital.

Question 24

How can methane’s tetrahedral geometry be explained?

Answer 24

Using four degenerate sp3-hybridized orbitals to achieve its four single bonds.

Question 25

How can ethylene’s planar geometry be explained?

Answer 25

Using three degenerate sp2-hybridized orbitals. The remaining p orbitals overlap to form a separate bonding interaction called a pi bond. The carbon atoms of ethylene are connected via a sigma bond, resulting from the overlap of sp2-hybridized atomic orbitals, and via a pi bond, resulting from the overlap of p orbitals, both of which comprise the double bond of ethylene.

Question 26

How is acetylene’s linear geometry achieved?

Answer 26

sp-hybridized carbon atoms in which a triple bond is created from the bonding interactions of one sigma bond, resulting from overlapping sp orbitals, and two pi bonds, resulting from overlapping p orbitals.

Question 27

How do the strengths and lengths of triple bonds compare to double and single bonds?

Answer 27

Triple bonds are stronger and shorter than double bonds, which are stronger and shorter than single bonds.

Question 28

When do dipole moments occur?

Answer 28

Dipole moments occur when the center of negative charge and the center of positive charge are separated from one another by a certain distance.

Question 29

What does the dipole moment measure?

Answer 29

The dipole moment is used as an indicator of polarity (measured in debyes). The percent ionic character of a bond is determined by measuring its dipole moment.

Question 30

What determines the molecular dipole moment?

Answer 30

The vector sum of individual dipole moments in a compound.

Question 31

What are intermolecular forces?

Answer 31

The attractive forces between molecules.

Question 32

Where do dipole-dipole interactions occur?

Answer 32

Between two molecules that possess permanent dipole moments.

Question 33

When does hydrogen bonding occur?

Answer 33

When the lone pairs of an electronegative atom interact with an electron-poor hydrogen atom.

Question 34

How do the boiling points of compounds that exhibit hydrogen bonding compare to those that lack hydrogen bonding?

Answer 34

Boiling points are higher in compounds that exhibit hydrogen bonding.

Question 35

What is the cause of London dispersion forces?

Answer 35

These forces are the result of the interaction between transient dipole moments and are stronger for larger alkanes due to their larger surface area and ability to accommodate more interactions.

Question 36

What is molecular orbital theory?

Answer 36

A mathematical combination of atomic orbitals to form orbitals that represent the electron density over an entire molecule.

Question 37

What are nodes?

Answer 37

Places where there is no electron density between a + and - phase.

Question 38

How is the number of atomic orbitals related to the number of molecular orbitals?

Answer 38

The number of atomic orbitals combined is equal to the final number of molecular orbitals.

Question 39

How do pi MOs overlap relative to the internuclear axis?

Answer 39

They overlap perpendicular to the internuclear axis.

Question 40

How do sigma MOs overlap relative to the internuclear axis?

Answer 40

They overlap along the internuclear axis.

Question 41

What is the difference between electronic and molecular geometry?

Answer 41

Electronic geometry is based on the steric number (the number of electron dense regions). Molecular geometry considers the lone pairs on the central atoms.

Question 42

What are ion-ion interactions?

Answer 42

• Full charges interacting with each other–needs a formal charge.
• Can be attractive or repulsive–strong.

Question 43

What are carbocations?

Answer 43

Carbons that lack a full octet and do not have 4 bonds.

Question 44

What are carbanions?

Answer 44

Carbons that typically have a lone pair.

Question 45

What is stabilization in terms of resonance?

Answer 45

When there is a charge and it is spread across multiple atoms, it is stabilizing in that one atom does not have to bear the full charge. Typically, more resonance structures lead to a more stable molecule/ion.

Question 46

What does allylic mean?

Answer 46

One away from a double bond.

Question 47

What are the 5 patterns to recognize when drawing resonance structures?

Answer 47

1. An allylic lone pair
2. An allylic positive charge
3. A lone pair adjacent to a positive charge
4. A pi bond between two atoms of differing negativity
5. Conjugated pi bonds in a ring

Question 48

Why can only one thing resonate per atom?

Answer 48

Electrons need to be in a p orbital that is aligned with the p orbital on adjacent carbons to resonate. Only one of the appropriately aligned orbitals exist on each carbon, so only one electron pair can occupy it.

Question 49

Is a double bond or lone pair more likely to resonate on an atom?

Answer 49

Only one double bond or lone pair can resonate on an atom. If there is a double bond it takes precedence because it is already delocalized to another carbon.

Question 50

What are the consequences of resonance on hybridization?

Answer 50

When an atom has multiple resonance forms, the hybridization of the atom is of the least-hybridized form (sp2 instead of sp3, etc)