CHEM 281 - CHAPTER 1 EXAM QUESTIONS WITH CORRECT ANSWERS LATEST UPDATE 2026
What does "valence electrons" mean? - Answers Electrons in an atom's outermost shell; they
determine bonding behavior.
How many valence electrons does each of the main organic atoms have? - Answers H: 1
C: 4
N: 5
O: 6
Halogens: 7
What is the octet rule? - Answers Atoms (except H) are most stable with 8 valence electrons.
How many bonds do the following atoms "prefer" to form: C, N, O, H, Halogens? - Answers C = 4
N = 3 (plus a lone pair)
O = 2 (plus 2 lone pairs)
H=1
Halogens = 1 (plus 3 lone pairs)
What are heteroatoms? - Answers Any atoms in an organic molecule that are not C or H (e.g., O, N, S,
halogens).
What is a covalent bond? - Answers Two atoms share an electron pair.
What is an ionic bond? - Answers One atom fully transfers electrons to another (forms
cations/anions).
What is electronegativity (EN)? - Answers An atom's ability to pull bonding electrons toward itself.
What is the EN trend relevant to organic chemistry? - Answers F > O > N > Cl > Br ≫ C > H
What is a polar covalent bond? - Answers A bond between atoms with different electronegativities,
creating partial charges.
What is a dipole? - Answers A separation of charge within a polar bond or molecule.
What are the steps for drawing a Lewis structure? - Answers 1. Count valence electrons
2. Draw a skeleton (central atom = usually carbon)
3. Add single bonds
4. Add lone pairs to complete octets
5. Add double/triple bonds if needed
6. Assign formal charges
In a Lewis structure, where do lone pairs belong? - Answers On heteroatoms or any atom that needs
electrons to complete an octet.
Formula for formal charge? - Answers FC = Valence e⁻ - (Lone pair e⁻ + ½ Bonding e⁻)
Typical formal charge patterns for oxygen? - Answers O with 3 LP + 1 bond = -1
O with 2 LP + 2 bonds = 0
O with 1 LP + 3 bonds = +1
Typical formal charge patterns for nitrogen? - Answers N with 1 LP + 3 bonds = 0
N with 4 bonds = +1
Typical formal charge patterns for carbon? - Answers 4 bonds = 0
3 bonds = +1
3 bonds + a LP = -1
What is resonance? - Answers When multiple valid Lewis structures exist that differ only in electron
placement, not atom placement.
What can move in resonance? - Answers Only electrons (lone pairs or π bonds), not atoms or σ
bonds.
What is a resonance hybrid? - Answers The actual molecule, which is a blend of all resonance
contributors.
Why does resonance stabilize molecules? - Answers Because electron density is delocalized over
multiple atoms, lowering energy.
What makes a resonance contributor "good"? - Answers All atoms have full octets
Minimal charge separation
Negative charges on electronegative atoms
Positive charges on less electronegative atoms
What are the shapes of s and p orbitals? - Answers s = spherical
p = dumbbell-shaped (px, py, pz)
What does "valence electrons" mean? - Answers Electrons in an atom's outermost shell; they
determine bonding behavior.
How many valence electrons does each of the main organic atoms have? - Answers H: 1
C: 4
N: 5
O: 6
Halogens: 7
What is the octet rule? - Answers Atoms (except H) are most stable with 8 valence electrons.
How many bonds do the following atoms "prefer" to form: C, N, O, H, Halogens? - Answers C = 4
N = 3 (plus a lone pair)
O = 2 (plus 2 lone pairs)
H=1
Halogens = 1 (plus 3 lone pairs)
What are heteroatoms? - Answers Any atoms in an organic molecule that are not C or H (e.g., O, N, S,
halogens).
What is a covalent bond? - Answers Two atoms share an electron pair.
What is an ionic bond? - Answers One atom fully transfers electrons to another (forms
cations/anions).
What is electronegativity (EN)? - Answers An atom's ability to pull bonding electrons toward itself.
What is the EN trend relevant to organic chemistry? - Answers F > O > N > Cl > Br ≫ C > H
What is a polar covalent bond? - Answers A bond between atoms with different electronegativities,
creating partial charges.
What is a dipole? - Answers A separation of charge within a polar bond or molecule.
What are the steps for drawing a Lewis structure? - Answers 1. Count valence electrons
2. Draw a skeleton (central atom = usually carbon)
3. Add single bonds
4. Add lone pairs to complete octets
5. Add double/triple bonds if needed
6. Assign formal charges
In a Lewis structure, where do lone pairs belong? - Answers On heteroatoms or any atom that needs
electrons to complete an octet.
Formula for formal charge? - Answers FC = Valence e⁻ - (Lone pair e⁻ + ½ Bonding e⁻)
Typical formal charge patterns for oxygen? - Answers O with 3 LP + 1 bond = -1
O with 2 LP + 2 bonds = 0
O with 1 LP + 3 bonds = +1
Typical formal charge patterns for nitrogen? - Answers N with 1 LP + 3 bonds = 0
N with 4 bonds = +1
Typical formal charge patterns for carbon? - Answers 4 bonds = 0
3 bonds = +1
3 bonds + a LP = -1
What is resonance? - Answers When multiple valid Lewis structures exist that differ only in electron
placement, not atom placement.
What can move in resonance? - Answers Only electrons (lone pairs or π bonds), not atoms or σ
bonds.
What is a resonance hybrid? - Answers The actual molecule, which is a blend of all resonance
contributors.
Why does resonance stabilize molecules? - Answers Because electron density is delocalized over
multiple atoms, lowering energy.
What makes a resonance contributor "good"? - Answers All atoms have full octets
Minimal charge separation
Negative charges on electronegative atoms
Positive charges on less electronegative atoms
What are the shapes of s and p orbitals? - Answers s = spherical
p = dumbbell-shaped (px, py, pz)
