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Organic Chemistry > Chapter One: Kekule and Lewis Dot Structure > Flashcards

Chapter One: Kekule and Lewis Dot Structure Flashcards

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1
Q

What is the atomic number (Z) of an element?

A

The number of protons in an atom, which defines the element

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2
Q

What is the mass number (A) of an element?

A

The sum of protons and neutrons in an atom

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3
Q

What are isotopes?

A

Atoms of the same element (same Z), but with different mass numbers (A)

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4
Q

How do you calculate the number of neutrons in an atom?

A

Neutrons = Mass number (A) - Atomic number (Z)

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5
Q

What are the four types of atomic orbitals?

A

s, p, d, f

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6
Q

How many electrons can each type of orbital can hold?

A

Electrons fill orbitals starting at the lowest energy level

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7
Q

What is Hund’s Rule?

A

Electrons occupy orbitals singly before pairing up with electrons

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8
Q

What is a chemical bond

A

The interaction that hold two atoms together

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9
Q

What happens when a bond forms

A

Energy is released

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10
Q

What happens when a bond breaks?

A

Energy is absorbed

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11
Q

What are the three types of bonds based on electronegativity (ΔEN)?

A

Covalent (0.0–0.5)
Polar Covalent (0.6–1.9)
Ionic (>2.0)

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12
Q

What type of bond does NH₃ (ammonia) have?

A

Polar covalent (ΔEN = 3.0 - 2.1 = 0.9)

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13
Q

What do Lewis Structure show that Kekulé structures often omit?

A

Lone pairs of electrons

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14
Q

What is the octet rule?

A

Atoms tend to gain, lose, or share electrons to achieve eight valence electrons.

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15
Q

What elements can exceed the octet rule?

A

Elements in period 3 or higher (e.g., P, S, Cl).

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16
Q

What is the typical bonding pattern of carbon in organic compounds?

A

Carbons form 4 bonds, no lone pairs

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17
Q

What is the formal change formula?

A

FC = Valence electrons - Nonbonding electrons - (Bonding electrons/2)

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18
Q

What must the sum of all formal charges in a molecule equal?

A

The total charge of the molecule.

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19
Q

What is a resonance structure?

A

A different way of arranging electrons in a molecule without changing atom positions

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20
Q

What does a resonance hybrid represent?

A

The true electron distribution, which is a mix of all valid resonance structures

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21
Q

What is the significance of dashed lines in resonance structures?

A

They indicate delocalized electrons

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22
Q

What particle determines the identity of an element?

A

The number of protons (atomic number, Z)

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23
Q

What is the difference between core and valence electrons?

A

Core electrons are in inner shells not involved in bonding, while valence electrons are in the outer most shell and participate in bonding

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24
Q

Why do atoms form chemical bonds?

A

To achieve stable electron configuration similar to noble gases

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25
What is the difference between an ionic and covalent bond?
Ionic bonds involve electron transfer, while covalent bonds involve electron sharing
26
What type bonds form between two identical nonmetals?
Pure (nonpolar) covalent bond because there is no electronegativity difference
27
What is resonance?
A way to represent delocalized electrons using multiple valid Lewis structures
28
What is the resonance hybrid?
The true structure, which is an average of all resonance forms
29
What is the purpose of calculating formal charge
To determine the most stable Lewis structure by minimizing formal charges
30
What does a negative formal charge indicate?
The atom has more electrons than its neutral valence number
31
What is VSEPR theory used for?
To predict molecular shape based on electron pair repulsion
32
What is hybridization?
Mixing of atomic orbitals to form new hybrid orbitals for bonding
33
What are the three subatomic particles and their charges?
Protons (+), Neutrons (0), Electrons (-)
34
How do you determine the number of neutrons in an isotope?
Mass number - Atomic number
35
Why do elements in the same group of the periodic table have similar properties?
They have the same number of valence electrons
36
What is the trend fir atomic radius across a period?
Decreases from left to right due to increased nuclear charge
37
What is the trend for ionization energy across a period?
Increases from left to right because atoms hold onto electrons more tightly
38
What are they two ways atoms achieve full octet?
By transferring or sharing electrons
39
Which bond is stronger: ionic or covalent?
It depends: Ionic bonds are strong in solids but easily break in water, while covalent bonds generally remain strong in solutions.
40
Why are polar covalent bonds different from nonpolar covalent bonds?
Polar covalent bonds have an unequal electron distribution due to a difference in solutions
41
Why are polar covalent bonds different from nonpolar covalent bonds?
Polar covalent bonds have an unequal electron distribution due to a difference in electronegativity
42
What is a dipole moment?
A measure of charge separation in a polar molecule
43
What happens to bond length as bond order increases?
Bond length DECREASES as bond order INCREASES (single > double > triple)
44
What are the steps to draw a Lewis structure
1. Count valence electron 2. Connect atoms with single bonds 3. Complete octets with lone pairs 4. Check formal charges and adjust if needed
45
What are three common exceptions to the octet rule
1. incomplete octet 2. expanded octet 3. odd-electron species (e.g. NO, NO2)
46
How do you choose the best resonance structure?
The one that minimizes formal charges and places negative charges on the most electronegative atoms.
47
What is the difference between electron geometry and molecular geometry?
Electron geometry considers all electron pairs, while molecular geometry considers only bonded atoms.
48
What are the three main types of intermolecular forces?
1. London dispersion forces (weakest, present in all molecules) 2. Dipole-dipole interactions (between polar molecules) 3. Hydrogen bonding (strongest, between H and N, O, or F)
49
What causes dipole-dipole interactions?
The attraction between oppositely charged poles of polar molecules.
50
Why do larger molecules have stronger dispersion forces?
lead to greater temporary dipoles.
51
What is the Bronsted-Lowty definition of an acid and a base?
Acid = proton (H⁺) donor, Base = proton (H⁺) acceptor.
52
What is a conjugate acid-base pair?
A pair of substances that differ by only one proton (H⁺).
53
What is the pH of a neutral solution
7.0 at 25°C.
54
How do strong acids and weak acids differ?
Strong acids fully ionize in solution, while weak acids only partially ionize.
55
Example of strong acids
HCl, H₂SO₄, HNO₃.
56
What happens to bond strength as bond order increases?
Increases (triple > double > single)
57
Why is a C=C bond stronger than a C-C bond but weaker than a C≡C bond?
Two pi bonds, making them the strongest
58
Which is easier to break?: a polar covalent bond or nonpolar covalent bond?
Polar covalent bonds are generally easier to break due to uneven electron distribution.
59
What is Valence Bond Theory?
A theory stating that a covalent bond is formed by the overlap of two singly-occupied atomic orbitals from different atoms
60
What is a sigma bond?
A bond formed by head-to-head orbital overlap, where electrons are located between the two nuclei.
61
What types of orbitals can form sigma bonds?
s-s, p-p, s-p, and hybrid orbital overlaps
62
Hy does VBT fail to fully explain bonding in molecules like methane?
It does not correctly predict molecular geometry or explain how carbon can form four equivalent bonds.
63
What is hybridization?
The mixing of atomic orbitals within the same atom to form new orbitals that can create covalent bonds.
64
What determines the hybridization of an atom?
The number of bonding domains (sigma bonds + lone pairs) around the atom.
65
How do you determine hybridization?
sp³ → 4 domains, sp² → 3 domains, sp → 2 domains.
66
What is a dipole moment?
A measure of bond polarity, determined by electronegativity differences and molecular shape.
67
What is difference between a bond dipole and a net dipole?
Bond dipole refers to individual bonds, while net dipole determines whether the entire molecule is polar.
68
What is the direction of a dipole vector?
From the less electronegative atom to the more electronegative atom.
69
What determines whether a molecule is polar?
The sum of bond dipoles and the molecular geometry.
70
How can a molecule have polar bonds but still be nonpolar?
If its shape causes symmetrical dipole cancellation (e.g., CCl₄).
71
What are the four ways to represent organic molecules
Molecular formula, Kekulé structures, condensed structures, skeletal structures.
72
What information does a molecular formula provide?
The types and number of atoms but no structural details
73
What is a Kekulé structure?
A structure where every bond is explicitly shown using lines.
74
What is a condensed structure?
A representation where C-H and some C-C bonds are not explicitly drawn (e.g., CH₃CH₂OH).
75
What is a skeletal structure?
A simplified structure where carbon atoms are represented by line intersections and hydrogen atoms are omitted.
76
How do you determine the number of hydrogen atoms attached to a carbon in a skeletal structure?
#H = 4 - (# of bonds to non-hydrogen atoms).
77
What is the Index of Hydrogen Deficiency (IHD)
calculation used to determine the number of pi bonds and rings in a molecule.
78
What is the formula for IHD?
IHD = (n + 1) - [(m - t)/2] n = number of carbon atoms m = number of hydrogen atoms t = number of halogen atoms
79
What does an IHD of 4 indicate?
The molecule has a combination of four pi bonds or rings (e.g., benzene).
80
What are constitutional isomers?
Compounds with the same molecular formula but different connectivity.
81
Do constitutional isomers have the same IHD?
Yes, because they have the same molecular formula.
82
What do wedges and dashes represent in 3D structures?
Wedges = Bonds coming out of the plane Dashes = Bonds going behind the plane
83
What does a ball-and-stick model show?
bond angles and atomic connectivity
84
What does a space-filling model show?
The relative volume of atoms in a molecule.

Organic Chemistry (4 decks)

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