Question

which term matches the definition: a covalent bond between atoms of different electronegativities.

covalent bond
polar covalent bond
ionic bond
nonpolar covalent bond

question 15 (0.0862 points)

name the following molecule:

$\ce{ch_{3}-ch-ch_{2}-ch-ch_{3}}$
$\ce{|}$ $\ce{|}$
$\ce{ch_{3}}$ $\ce{ch_{3}}$

2,4-dimethylpentane
2,4 heptane
2,4-methylheptane
2,4-dimethyl-2-pentene

Explanation:

First Question (Term Matching)

To solve this, we analyze each option:

• covalent bond: A general term for a bond where electrons are shared, but it doesn't specify electronegativity difference.
• polar covalent bond: Defined as a covalent bond between atoms with different electronegativities (causing a dipole moment).
• ionic bond: Involves transfer of electrons, not sharing, so not a covalent bond.
• nonpolar covalent bond: Occurs between atoms with similar electronegativities (no significant difference).

So the term matching the definition is "polar covalent bond".

Step1: Identify the Parent Chain

The molecule has a carbon chain. Let's count the carbons: The main chain (longest) has 5 carbons? Wait, no. Wait, the structure is \( \text{CH}_3 - \text{CH}(\text{CH}_3) - \text{CH}_2 - \text{CH}(\text{CH}_3) - \text{CH}_3 \). Wait, no, let's count again. Wait, the given structure: \( \text{CH}_3 - \text{CH} - \text{CH}_2 - \text{CH} - \text{CH}_3 \) with \( \text{CH}_3 \) on the second and fourth carbons (numbering from left). Wait, the longest chain is 5 carbons? Wait, no, wait: Let's number the carbons. Let's write the structure properly. The parent chain: Let's count the number of carbons in the longest continuous chain. The structure is:

Carbon 1: \( \text{CH}_3 \)

Carbon 2: \( \text{CH} \) (with \( \text{CH}_3 \) attached)

Carbon 3: \( \text{CH}_2 \)

Carbon 4: \( \text{CH} \) (with \( \text{CH}_3 \) attached)

Carbon 5: \( \text{CH}_3 \)

Wait, no, that's 5 carbons? Wait, no, wait, the formula: Let's count the carbons. The main chain is 5 carbons? Wait, no, wait, the structure is \( \text{CH}_3 - \text{CH}(\text{CH}_3) - \text{CH}_2 - \text{CH}(\text{CH}_3) - \text{CH}_3 \). So the parent chain is pentane (5 carbons). Now, the substituents: methyl groups on carbon 2 and carbon 4. So the name is 2,4 - dimethylpentane. Let's check the options:

• 2,4 - dimethylpentane: Matches (parent chain pentane, two methyl groups on C2 and C4).
• 2,4 heptane: Heptane has 7 carbons, but our parent chain is 5, so wrong.
• 2,4 - methylheptane: Heptane (7 carbons) and wrong substituents, so wrong.
• 2,4 - dimethyl - 2 - pentene: The molecule has single bonds (all \( \text{CH}_2 \) and \( \text{CH} \) with single bonds), so it's an alkane, not an alkene (no double bond), so wrong.

Step2: Confirm the Naming

The IUPAC naming: Parent chain (pentane, 5 carbons), substituents (two methyl groups at positions 2 and 4), so 2,4 - dimethylpentane.

Answer:

B. polar covalent bond (assuming the options are labeled A: covalent bond, B: polar covalent bond, C: ionic bond, D: nonpolar covalent bond)

Second Question (Naming the Molecule)