CHEM219 / CHEM 219 Module 1: (Latest Update
2026 / 2027) Principles of Organic Chemistry
with Lab | Questions & Answers | Grade A | 100%
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2026 / 2027 Academic Year
Q: On a piece of scratch paper, write out the Lewis Dot Diagram for each of the indicated
elements and determine the following for each:
Answer
a) The number of Lone Pairs the atom possesses in its valence shell.b) The number of
Unpaired Electrons the atom possesses in its valence shell.c) The number of bonds the
atom will form.
Oxygen
Carbon
Hydrogen
Nitrogen
Oxygen - a) 2 b) 2 c) 2
Carbon - a) 0 b) 4 c) 4
Hydrogen- a) 0 b) 1 c) 1
Nitrogen - a) 1 b) 3 c) 3
Q: Classify the bonding between the given pairs of atoms as ionic, covalent, or polar
covalent. Use the table of electronegativities shown below to help with the classification.
a. Br and Br
b. K and Cl
c. P and Cl
d. C and O
e. Na and Br
Answer
a. Br-Br: Electronegativity difference () = 0 = COVALENT (or pure covalent)
b. K-Cl: () = 2.2 = IONIC
c. P-Cl: ()= 0.9 = POLAR COVALENT
d. C-O: ()= 1.0 = POLAR COVALENT
e. Na-Br: () = 1.8 = POLAR COVALENT
Q: Define the term constitutional isomer.
Answer
Two (or more) different chemical compounds with the same molecular formula but
different connectivity between the atoms in their structural formulae.
Q: Explain (using specific evidence) what makes the following two compounds
constitutional isomers of one another:
Answer
Both compounds have a MF of C3H6O - same MF.
Compound "a" has a 3-carbon chain with a C=O in the middle. No H atom connected to C of
C=O.
Compound "b" has a 3-carbon chain with a C=O at the end. There is an H attached to the C
of the C=O.
Q: What is the relationship between the compounds shown? Are they the same
compound, constitutional isomers, or two different compounds that are not related to one
another? Explain.
Answer
Different compounds that are not related. They have different MF - (a) C3H8O, (b) C3H6O.
Q: Identify each of the following carbon skeletons as linear (continuous), branched, or
cyclic.
Answer
a) Branched
b) Linear (continuous)
c) Cyclic
Q: On a piece of scratch paper, write out structural formulae for all of the constitutional
isomers possible for the MF C3H6F2. How many isomers are possible for this formula?
Answer
4
Q: Characterize each of the following structural formula representations as either a dash,
condensed, super-condensed, or bond-line formula:
Answer
a) Super-Condensed
b) Condensed
c) Bond-line
d) Dash
Q: Write the molecular formula for each of the compounds whose bond-line formulae are
given below.
Answer
a) C5H10
b) C3H8O
c) C4H10O
Q: Which bond-line formula shown below represents a constitutional isomer of
CH3CH2CH2CH2CH3?
Answer
(b)
Q: Which of the following structures does NOT have the molecular formula C6H14?
Answer
(d)
Q: The structural formula:
Has what molecular formula?
Answer
(c) C7H14
Q: The compound carbon monoxide has the following structural formula:
What is the formal charge on the carbon and the oxygen? Show your calculation. What is
the overall charge on the molecule?
Answer
Carbon = 4-(2+3) = -1
Oxygen = 6-(2+3) = +1
Overall = FC Carbon + FC Oxygen = [-1 + (+1)] = 0
Q: For the following example of resonance:
Answer
Which structure (a or b) represents a "major" resonance contributor to the hybrid? Briefly
explain why.
Structure "a" is a major contributor. All of the atoms have complete valences and in
addition, all of the atoms have a formal charge of zero (All of the atoms are meeting their
LDD bonding pattern).
Q: Describe how individual resonance structures impact the true structure of a molecule
or polyatomic ion.
Answer
Each contributing individual resonance structure contributes characteristics to the overall
hybrid structure of the compound. The hybrid "averages" bond lengths and formal charges
by delocalizing them among atoms that share them in each contributing individual
resonance structure.
Q: On a piece of scrap paper, draw the resonance structure "b" that would result from
redistributing the electrons as shown on structure "a" in the diagram below:
For your structure "b", complete the table with the information requested:
Answer
Oxygen: 1 lone pair, 1 single bond, 1 double bond, +1 formal charge.
Carbon (1): 0 lone pair, 2 single bond, 1 double bond, 0 formal charge.
Carbon (II): 1 lone pair, 3 single bond, 0 double bond, -1 formal charge.
Q: Describe the shapes associated with the atomic orbitals associated with the main
elements of organic chemistry.
Answer
S orbitals are spherical (single lobe), while P orbitals are dumbbell-shaped (two lobes).
End-on overlap of atomic orbitals leads to the formation of sigma (single) covalent bonds.
Sideways overlap of P orbitals leads to the formation of pi (multiple) covalent bonds.
Q: Explain how bonds are formed between atoms from the perspective of atomic orbital
theory.
Answer
Atoms form bonds by overlapping individual atomic orbitals from each atom to produce
molecular (bonding) orbitals.
Q: Explain the two types of atomic orbital overlap that contribute to bond formation in
organic molecules.
Answer
Q: Using the VSEPR method, predict the molecular geometry (shape and bond angle)
around the indicated atoms for the following structure:
a) C(I)
b) C(II)
c) N
d) S
Answer
a) C(I) = 4 bond pairs = TETRAHEDRAL, 109.5°
b) C(II) = 3 bond pairs = TRIGONAL PLANAR, 120°
c) N = 3 bond pairs/1 lone pair = TRIGONAL PYRAMIDAL, 107°
d) S = 2 bond pairs/2 lone pairs = ANGULAR/BENT, 105°
Q: Catenation
Answer
The process or preference of an element to link/bond with another atom of the same
element.
Q: Ionic bond
Answer
***formed by the sharing of electrons - electronegativity diff: < 0.4 (zero difference)
***the complete transfer of one or more valence electrons from one atom to another - electronegativity diff > 1.8 (large)
Q: (Pure) Covalent bonds
Answer
Q: Diatomic element
Answer
When an atom is more stable when bonded to another atom
Q: Pure covalent bond
Answer
***A bond that forms between atoms of identical electronegativity values. (aka shared
electrons) - electronegativity diff < 0.4 (zero)
Q: Polar covalent bond
Answer
***Bond that occurs when atoms are shared unequally. - electronegativity diff: Between 0.4 and 1.8
Unsaturated compound
Answer
Molecules that posses one or more double or triple bonds (or a ring) as part of their
structure.
Isomer
Answer
Molecules with the same molecular formula but a different structure, and therefore a
different shape. - constitutional or structural isomers
Formal charge formula
Answer
FC = group # of element - (dots + dashes)
- dots = non-binding electrons (lone pair or single unpaired electrons) - dashes = bonding electrons
Resonance structure
Answer
Two or more structural formula of a molecule with identical arrangements of atoms BUT
different arrangements of electrons
Major contributor
Answer
Ideal arrangement/structure
Minor contributor
Answer
Less ideal arrangement/structure
Non-contributor
Answer - associated with P orbitals only - Pi orbital
Arrangement/structure does not match or correlate with correct atoms/electrons in an
element.
End-on overlap molecules
Answer
The binding/combination of either S or P orbitals, or both
Sideways orbital overlap
Answer
Valence shell electron pair repulsion (VSEPR) theory
A tool for determining the shape around atoms in molecules based on analysis of the
patterns of electrons around them. - electrons repel (want to be far apart from each other)
Molecular geometry - wedge bond: project out of plane of paper (towards us) - dash bond: project behind plane of paper (away from us) - line bond: rep atoms/groups that remain in plane of paper
Cation
Becomes positively charged when it loses an electron
Anion
Becomes negatively charged when it receives an electron
The properties & reactivity of an organic molecule are controlled by its
composition & shape
What is organic chemistry?
Branch of chemistry that studies the structure, properties, composition, reaction and
synthesis of organic compounds which contain carbon atoms.
Catenation
Ability of ab element to form bonds with itself, resulting in formation of chains, rings or
complex structures.
Allows for vats diversity of organic compounds in terms of reactivity and properties
Why do atoms form bonds to other atoms?
Energetic stability
To say an atom is energetically stable means that the overall energy of the atom is
lower when in the bonded state than in a non bonded state
T/F
Lower energy typically means greater stability? Why
True
b/c the electron configuration of the atom - atomic valence
Valence
# of bonds an atom will form to fill its valve (outermost) shell.
The atom achieves stability from a full valence shell, as there is no desire to make bonds
Knowing the valence of an atom is important because it indicates ...
How many bonds a given atom will typically form when it combines with other elements to
make a molecule
What do you look at to figure out how many bonds an element will form
LDD
Comes from group number
Unpaired electrons
# of bonds the atom will form
# of pairs of electrons
LONE pairs or nonbonding , these do not participate in bonding
Ionic bonds
formed by the complete transfer of 1 or more valence electron from 1 atom to another
Cation
The atom that loses an electron becomes positively charged
Anion
The atom that gains an electron, becomes negatively charged
Ion
Chemical species that possesses a non-zero electrical charge.
An ionic bond is the attractive force bt oppositely charged ions - an electrostatic attraction
(opposites attract)
How does electronegativity (X) increase
increases moving towards the right and going up the PTOTE
Covalent Bonds
share electrons bt elements with little or no difference in their electronegativity - Heat is released when covalent bonds are formed
Diatomic Elements
a molecule composed of only 2 atoms of the same element. In their natural state, these
elements exist as diatomic molecules rather than individual atoms b/c they are more stable
in this paired form
Key parameters of a covalent bond
Bond strength
bond length
Bond strength
determined by how much heat is released when covalent bond forms (atoms lose energy in
form of heat), gain stability
Chemical term used to describe the energy/stength of a covalent bond is known as
bond enthalpy
Bond length
distance that described the perfect balance bt attraction and repulsion
the atoms vibrate around each other at some equilibrium point, neither flying apart or
fusing together
What determines the number of bonds an atom can form
The number of unpaired electrons
Do lone pairs bond
No
Cation
Loses electron and becomes positive
Ionic bond
The transfer of a valence electron to another atom
Anion
Gains electron and becomes negative
Covalent bond
Sharing of electrons
Pure covalent bond
Identity of atoms is the same
Polar covalent bond
Unequal sharing of electrons
EN difference of 0
Pure covalent
EN difference of 0-0.5
Covalent
EN difference of 0.5-2.0
Polar covalent
EN difference above 2.0
Ionic
Bond order
The number of bonds between atoms: 1 for a single bond, 2 for a double bond, and 3 for a
triple bond
Unsaturation
Lack of hydrogen due to the catenation of carbon
Constitutional isomers
Same molecular formula, but different connectivity
Heteroatoms
Atoms other than C and H
Condensed formula
CH3CH2CH2CH3
Super-condensed formula
CH3(CH2)CH3
Formal charge
Atoms that do not meet the LDD bonding pattern and possess non-zero charge
Calculate formal charge
Group number - (Dots + Dashes)
Overall charge
Sum of formal charges
Hybrid resonance
The average of all resonance structures
What gets changed in resonance
Lone pairs -> Multiple bonds OR Multiple bonds -> Lone pairs
Never single bonds
Major contributors to resonance
Completes the valence
Orbital
Space around nucleus with high probability of finding an electron
Node
Center of orbital, unlikely to find an electron
Which orbitals are in ochem
S&P (spherical and dumbell)
Combination of orbitals theory
A bond between atoms is due to an overlap of their atomic orbitals, resulting in a bonding
molecular orbital
Sigma bond
End on overlap, circular symmetry around bond axis, in hybrid orbitals
Pi bond
Sideways overlap of orbitals
2 bonding 0 lone
Linear, 180
2 bonding 1 lone
angular/bent, 107
3 bonding 0 lone
trigonal planar, 120
3 bonding 1 lone
trigonal pyramidal, 107
2 bonding 2 lone
angular/bent, 105
4 bonding 0 lone
tetrahedral, 109.5
What do you count double bonds as in VSPER
A single pair
Linear
180°
2 BE
0 LP
Angular (2 total electron pairs)
107°
2 BE
1 LP
Trigonal Planar
120°
3 BE
0 BE
Trigonal Pyramidal
107°
3 BE
1 LP
Angular/Bent (4 total electron pairs)
105°
2 BE
2 LP
Tetrahedral
109.5°
4 BE
0 LP
Bond Type for 0 difference in EN?
Purely Covalent
(usually elements to themselves)
Bond Type for > 0 but </= 0.5
Covalent
Bond Type for > 0.5 by </= 2.0
Polar Covalent
Bond Type for >/= 2.0
Ionic
Ionic Bond Melting Point
Very High
Covalent Bond Melting Point
Lower than 300 C
Ionic Physical State
Brittle, Crystalline
Covalent Physical State
Solid, gas, liquid
Covalent Solubility
Range of solubilities
Ionic Solubility
Dissolves readily in polar solvents
Ionic Conduction
Aqueous solutions conduct electricity
Covalent Conduction
Aqueous solutions do NOT conduct electricity
Formal Charge Formula
FC = Group # - (Dots + Dashes)
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