Draw the Lewis structure of BH3.
The Correct Answer and Explanation is:
Correct Lewis Structure for BH₃:
To draw the correct Lewis structure for borane (BH₃):
- Place the boron (B) atom in the center since hydrogen (H) can form only one bond and cannot be the central atom.
- Attach three hydrogen atoms to the boron atom using single bonds.
- Do not add lone pairs to hydrogen, as each hydrogen only needs 2 electrons (1 bond).
- Boron will have only 6 electrons (3 bonds), which is an exception to the octet rule.
Lewis Structure:
H
|
H — B — H
Each line represents a bonding pair of electrons.
Explanation
The Lewis structure of BH₃ (borane) illustrates the bonding arrangement between boron and hydrogen atoms. BH₃ is a molecule composed of one boron (B) atom and three hydrogen (H) atoms. To draw the Lewis structure, we begin by determining the number of valence electrons:
- Boron (Group 13): 3 valence electrons
- Hydrogen (Group 1): 1 valence electron × 3 = 3
- Total = 3 (B) + 3 (H) = 6 valence electrons
In the Lewis structure, the boron atom is placed at the center with three single bonds connecting it to three hydrogen atoms. Each single bond (B–H) consists of 2 electrons. Thus, 3 bonds use all 6 available valence electrons.
Hydrogen atoms follow the duet rule, meaning they are stable with 2 electrons (1 bond). Each H atom in BH₃ forms a single bond with B, which satisfies this requirement.
Boron, however, is an exception to the octet rule. In BH₃, boron has only 6 electrons around it (3 single bonds), making it electron-deficient. It does not have a complete octet, but this is acceptable for boron compounds, especially in small molecules like BH₃.
This electron deficiency makes BH₃ highly reactive; it often acts as a Lewis acid, meaning it can accept a pair of electrons to complete its octet. In chemistry, BH₃ is often seen in reactions where it forms adducts with Lewis bases.
In summary, the Lewis structure for BH₃ is a simple molecule with three B–H bonds and no lone pairs. It illustrates key concepts such as exceptions to the octet rule and the stability of hydrogen with only two electrons.
