Textbook Question
Which of the following elements is the best conductor of electricity? (LO 22.1)
(a) N (b) As
(c) P (d) Bi
Ch.22 - The Main Group Elements
Chapter 22, Problem 5
Draw the electron-dot structure for BH3. What are the hybrid orbitals used by boron to form bonds with hydrogen, and will BH3 act as a Lewis acid or a Lewis base? (LO 22.9) (a) sp3; Lewis acid (b) sp3; Lewis base (c) sp2; Lewis acid (d) sp2; Lewis base
Verified step by step guidance1
Step 1: Determine the total number of valence electrons in BH3. Boron (B) has 3 valence electrons, and each hydrogen (H) has 1 valence electron. Therefore, the total number of valence electrons is 3 (from B) + 3*1 (from 3 H) = 6 valence electrons.
Step 2: Draw the electron-dot structure for BH3. Place boron in the center and arrange the three hydrogen atoms around it. Distribute the 6 valence electrons to form single bonds between boron and each hydrogen atom, resulting in a structure where boron is surrounded by three hydrogen atoms, each sharing a pair of electrons with boron.
Step 3: Determine the hybridization of boron in BH3. Boron forms three sigma bonds with hydrogen, and there are no lone pairs on boron. The steric number (number of sigma bonds + lone pairs) is 3, indicating sp2 hybridization.
Step 4: Analyze whether BH3 acts as a Lewis acid or a Lewis base. A Lewis acid is an electron pair acceptor, while a Lewis base is an electron pair donor. Since BH3 has an incomplete octet and can accept an electron pair, it acts as a Lewis acid.
Step 5: Based on the analysis, the correct answer is (c) sp2; Lewis acid.
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Electron-Dot Structure
The electron-dot structure, or Lewis structure, represents the valence electrons of atoms within a molecule. In BH3, boron is the central atom surrounded by three hydrogen atoms, with each bond represented by a pair of shared electrons. This structure helps visualize how atoms are bonded and the distribution of electrons, which is crucial for understanding molecular geometry and reactivity.
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Lewis Dot Structures: Ions
Hybridization
Hybridization is the concept of mixing atomic orbitals to form new hybrid orbitals that can accommodate bonding. In the case of BH3, boron undergoes sp2 hybridization, resulting in three equivalent sp2 hybrid orbitals that form sigma bonds with hydrogen atoms. This hybridization influences the molecular shape and bond angles, leading to a trigonal planar geometry.
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Lewis Acids and Bases
Lewis acids are defined as electron pair acceptors, while Lewis bases are electron pair donors. In the context of BH3, the molecule acts as a Lewis acid because boron has an incomplete octet and can accept a pair of electrons to achieve stability. This property is significant in chemical reactions, particularly in coordination chemistry and organic synthesis.
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Related Practice
Textbook Question
Which element will react most vigorously with water, and what is the reaction that occurs?
(a) Lithium; 2 Li(s) + 2 H2O(l) → 2 Li+(aq) + 2 H–(aq) + H2O2(aq)
(b) Potassium; 2 K(s) + 2 H2O(l) → 2 K+(aq) + 2 OH–(aq) + H2(g)
(c) Magnesium; Mg(s) + 2 H2O(l) → Mg2+(aq) + 2 OH–(aq) + H2(g)
(d) Barium; Ba(s) + 2 H2O(l) → Ba2+(aq) + 2 H–(aq) + H2O2(aq)