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

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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.

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Flashcard 1: 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 2: 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 3: 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 4: 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 5: 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 6: 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 7: 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 8: 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 9: 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 10: 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 11: 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 12: 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 13: 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 14: 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.

Flashcard 15: 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 16: 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 17: 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 18: 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 19: 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 20: 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 21: 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 22: 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 23: 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 24: 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 25: 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.