Question

select the lewis structure that most accurately represents boron trihydride (bh₃). refer to a periodic table.

Explanation:

Step1: Determine valence electrons

Boron (B) has 3 valence electrons, hydrogen (H) has 1 each. For \( \text{BH}_3 \), total valence electrons: \( 3 + 3\times1 = 6 \).

Step2: Analyze bonding

Boron is the central atom. Each H forms a single bond (2 electrons) with B. Single bonds use 2 electrons per bond, 3 bonds use \( 3\times2 = 6 \) electrons, which matches total valence electrons. Boron has 6 electrons (octet exception, it's a Lewis acid, stable with 6 in \( \text{BH}_3 \)).

- First structure: Double bond (incorrect, H can't double bond, and electrons would exceed).
- Second structure: Lone pairs on H (incorrect, H has 2 electrons in bond, no lone pairs).
- Third structure: Three single bonds (B - H), each H has 2 electrons, B has 6 (3 bonds × 2), correct.
- Fourth structure: Lone pair on B? Wait, no—wait, \( \text{BH}_3 \) has B with 3 bonds, no lone pairs on B (since total electrons are 6, 3 bonds). Wait, the fourth structure: let's check again. Wait, the third structure (bottom left) and fourth (bottom right). Wait, bottom right: H - B - H with H below. Wait, no—wait, the third structure (bottom left) has three single bonds, B in center, three H attached with single bonds. That's correct because B has 3 valence electrons, each H donates 1, so 3 bonds (6 electrons), no lone pairs on B (since 3 + 3×1 = 6, all used in bonding). The fourth structure: does it have a lone pair on B? Wait, the diagram: bottom right is H - B - H with H below, and B has two dots (lone pair)? No, wait, no—wait, the problem's structures: let's re-express.

Wait, correct Lewis structure for \( \text{BH}_3 \): central B, three single bonds to H. Each H has 2 electrons (in bond), B has 6 (3 bonds × 2). So the structure with three single bonds (no double bonds, no lone pairs on H or extra on B) is correct. The bottom left (third structure) or bottom right? Wait, bottom right: H - B - H, H below. Wait, no, the bottom left is:

H

|

B - H

/

H

And bottom right is:

H - B - H

|

H

Both are trigonal planar, but the key is valence electrons. Wait, the third structure (bottom left) and fourth (bottom right) – wait, the fourth structure: does B have a lone pair? The diagram shows B with two dots? Wait, no, maybe the user's diagram: let's re-express the options:

1. Top left: H double bond B, two single bonds (incorrect, H can't double bond, B would have too many electrons).

2. Top right: H single bond B, two H with lone pairs (incorrect, H has no lone pairs).

3. Bottom left: Three single bonds (B - H), no lone pairs, correct.

4. Bottom right: H - B - H, H below, and B has two dots (lone pair)? No, that would be 8 electrons on B (3 bonds × 2 + 2 lone = 8), but total valence electrons are 6, so that's incorrect. Wait, no—wait, \( \text{BH}_3 \) has 6 valence electrons. If B has a lone pair (2 electrons), then bonding electrons would be 4 (2 bonds), plus lone pair 2, total 6? No, that's not. Wait, no—B has 3 valence electrons. Each H contributes 1. So 3 + 3 = 6. So 3 bonds (each 2 electrons) = 6. So B has 6 electrons (3 bonds), no lone pairs. So the structure with three single bonds, no lone pairs on B, is correct. So the bottom left (third structure) or bottom right? Wait, the bottom right: H - B - H, H below. Wait, maybe the bottom right is the same as bottom left, just drawn differently. Wait, no—wait, the third structure (bottom left) is:

H

|

B - H

/

H

And bottom right is:

H - B - H

|

H

Both are trigonal planar, but the key is no double bonds, no lone pairs on H, and B with 3 single bonds. So the correct structure is the one with three single bonds, which is the bottom left (third option) or bottom right? Wait, the user's options:

Top left: H double bond B, two single bonds (wrong).

Top right: H single bond B, two H with lone pairs (wrong, H can't have lone pairs).

Bottom left: Three single bonds (B - H), no lone pairs (correct).

Bottom right: H - B - H, H below, and B has two dots? Wait, no, maybe the bottom right is a typo, but the bottom left is correct. Wait, no—wait, the fourth structure (bottom right) in the diagram: let's see, the user's image: bottom right is "H - B - H" with "H" below, and B has two dots? No, maybe the bottom left is correct. Wait, actually, the correct Lewis structure for \( \text{BH}_3 \) is three single bonds, so the structure with three single bonds (no double bonds, no extra lone pairs) is the third one (bottom left) or fourth? Wait, no, the bottom right: H - B - H, H below. That's also three single bonds. Wait, maybe the difference is in the drawing, but the key is that B has three single bonds, no lone pairs, and H has no lone pairs. So the correct one is the bottom left (third structure) or bottom right? Wait, no—wait, the bottom left:

H

|

B - H

/

H

And bottom right:

H - B - H

|

H

Both are three single bonds. Wait, but the bottom right: does B have a lone pair? The diagram shows B with two dots? Wait, no, maybe the user's diagram: the bottom right has B with two dots (lone pair), which would be incorrect (since that would be 8 electrons on B, but \( \text{BH}_3 \) has 6). Wait, no—wait, \( \text{BH}_3 \) has B with 3 valence electrons, so 3 bonds (6 electrons), no lone pairs. So the structure with no lone pairs on B is correct. So the bottom left (third structure) has no lone pairs on B, three single bonds. The bottom right: if B has a lone pair (two dots), that's incorrect. So the correct structure is the bottom left (third option) or the one with three single bonds. Wait, the third structure (bottom left) is:

H

|

B - H

/

H

Which is three single bonds, B has 6 electrons (3 bonds × 2), H has 2 each. Correct.

Answer:

The Lewis structure with three single bonds (B in center, three H attached via single bonds, no double bonds or extra lone pairs) – specifically the bottom - left structure (or the one with three single B - H bonds, no lone pairs on B or H with extra electrons). If we assume the options are labeled (let's say top - left: 1, top - right: 2, bottom - left: 3, bottom - right: 4), then the correct one is 3 (bottom - left) or the structure with three single bonds.