MCAT Chemical and Physical Foundations of Biological Systems Flashcards: 5b Covalent Bonding Lewis Structures

What this deck covers

This deck focuses on 5b Covalent Bonding Lewis Structures, giving you a quick way to review the definitions, rules, and examples that matter most for MCAT Chemical and Physical Foundations of Biological Systems.

How to use these flashcards

Work through these flashcards in short sessions. Try to answer each prompt before flipping the card, then revisit any cards you miss until the explanation feels automatic.

Flashcard 1: What is the maximum number of electrons that can be placed around hydrogen in a Lewis structure?

Answer: $2$ electrons. Hydrogen's $1s$ orbital limits it to $2$ electrons, mimicking helium's stable configuration.

Flashcard 2: What is the typical bonding pattern of carbon in neutral organic Lewis structures?

Answer: Carbon typically forms $4$ bonds and has $0$ formal charge. Carbon's $4$ valence electrons lead to $4$ bonds to reach an octet, resulting in zero formal charge in neutral molecules.

Flashcard 3: What is the correct description of a resonance hybrid compared with any single resonance structure?

Answer: The real structure is a weighted average of resonance contributors. The resonance hybrid provides a more accurate depiction by averaging electron distributions from contributing structures.

Flashcard 4: What is the bond order associated with a double bond in Lewis structures?

Answer: Bond order $=2$. A double bond involves two shared electron pairs, defining bond order $2$ in Lewis structures.

Flashcard 5: What is an expanded octet, and which period elements commonly show it in Lewis structures?

Answer: More than $8$ electrons; common for period $3$ and below (e.g., P, S, Cl). Expanded octets occur due to available $d$ orbitals in period $3+$ elements, allowing more than $8$ electrons.

Flashcard 6: What is the formula for formal charge on an atom in a Lewis structure?

Answer:  ext{FC}= ext{valence}- ext{nonbonding}-rac{ ext{bonding}}{2}. The formula calculates deviation from neutral electron count, aiding in evaluating Lewis structure validity.

Flashcard 7: Identify the total valence electron count for $ext{CO}_3^{2-}$ for drawing its Lewis structure.

Answer: $24$ valence electrons. Valence count includes carbon's $4$, three oxygens' $18$, plus $2$ electrons for the $2-$ charge.

Flashcard 8: What is the typical bonding pattern of oxygen in neutral Lewis structures (bonds and lone pairs)?

Answer: $2$ bonds and $2$ lone pairs. Oxygen's $6$ valence electrons necessitate $2$ bonds and $2$ lone pairs for octet completion in neutral Lewis structures.

Flashcard 9: What is the typical bonding pattern of nitrogen in neutral Lewis structures (bonds and lone pairs)?

Answer: $3$ bonds and $1$ lone pair. Nitrogen's $5$ valence electrons require $3$ bonds and $1$ lone pair to complete an octet in neutral structures.

Flashcard 10: What is the definition of a covalent bond in terms of electron behavior?

Answer: A bond formed by sharing one or more electron pairs between atoms. Covalent bonds stabilize atoms by allowing them to share electrons, achieving lower energy configurations similar to noble gases.

Flashcard 11: Which elements commonly follow the duet rule in Lewis structures?

Answer: Hydrogen and helium (stable with $2$ valence electrons). Hydrogen and helium achieve stability with a helium-like configuration of $2$ valence electrons due to their small size.

Flashcard 12: What is the definition of a resonance structure in Lewis theory?

Answer: One of multiple valid Lewis drawings differing only in electron placement. Resonance structures represent different electron distributions for the same atomic arrangement, illustrating delocalization.

Flashcard 13: Which resonance contributor is generally most important: full octets or incomplete octets (main-group)?

Answer: The contributor with full octets is generally most important. Structures with full octets are more stable due to achieving noble gas-like electron configurations.

Flashcard 14: Identify the total valence electron count for $ext{NO}_3^-$ for drawing its Lewis structure.

Answer: $24$ valence electrons. Total valence electrons sum nitrogen's $5$, three oxygens' $18$, plus $1$ for the negative charge.

Flashcard 15: What is the bond order associated with a single bond in Lewis structures?

Answer: Bond order $=1$. A single bond represents one shared electron pair, corresponding to bond order $1$ in Lewis notation.

Flashcard 16: What is the typical bonding pattern of halogens in neutral Lewis structures (bonds and lone pairs)?

Answer: $1$ bond and $3$ lone pairs. Halogens' $7$ valence electrons lead to $1$ bond and $3$ lone pairs to achieve an octet in neutral compounds.

Flashcard 17: Identify the formal charge on oxygen with $6$ valence e$^-$, $6$ nonbonding e$^-$, and $2$ bonding e$^-$.

Answer: $-1$. Applying the formal charge formula yields $-1$, indicating an extra electron on oxygen compared to neutral.

Flashcard 18: Which bond is shortest: single, double, or triple (between the same two elements)?

Answer: Triple bond is shortest. Higher bond orders increase electron density between nuclei, pulling atoms closer and shortening bond length.

Flashcard 19: Which three elements commonly violate the octet rule by being electron-deficient in Lewis structures?

Answer: Boron, beryllium, and aluminum. These elements often form stable compounds with fewer than $8$ electrons due to their electron configurations.

Flashcard 20: Identify the number of valence electrons in a neutral sulfur atom for Lewis structure counting.

Answer: $6$ valence electrons. Sulfur, in group $16$, has $6$ valence electrons as determined by its periodic table position.

Flashcard 21: Identify the formal charge on nitrogen with $5$ valence e$^-$, $0$ nonbonding e$^-$, and $8$ bonding e$^-$.

Answer: $+1$. The formal charge calculation shows $+1$, as nitrogen has fewer electrons than its neutral valence count.

Flashcard 22: What is the octet rule for main-group elements in Lewis structures?

Answer: Atoms tend to form bonds to achieve $8$ valence electrons. The octet rule reflects the stability of noble gas electron configurations, guiding bond formation in Lewis structures.

Flashcard 23: Which bond is strongest: single, double, or triple (between the same two elements)?

Answer: Triple bond is strongest. Greater bond order involves more shared electrons, requiring higher energy to break the bond.

Flashcard 24: Which resonance contributor is favored regarding formal charges on atoms?

Answer: Minimized formal charges, with negative charge on more electronegative atoms. Lower formal charges enhance stability, and electronegative atoms better accommodate negative charges.

Flashcard 25: What is the bond order associated with a triple bond in Lewis structures?

Answer: Bond order $=3$. A triple bond consists of three shared electron pairs, establishing bond order $3$ in Lewis theory.