Question

Borazine \(\left(\mathrm{B}_{3} \mathrm{N}_{3} \mathrm{H}_{6}\right)\) has often been called "inorganic" benzene. Write Lewis structures for borazine. Borazine contains a six-membered ring of alternating boron and nitrogen atoms with one hydrogen bonded to each boron and nitrogen.

Short answer

The Lewis structure for borazine \(\mathrm{(B}_{3} \mathrm{N}_{3} \mathrm{H}_{6})\) can be drawn as follows: ``` H | N = B - N | | B - N = B | H ``` The structure consists of a six-membered ring with alternating boron and nitrogen atoms, with each atom bonded to a hydrogen. The octet rule is satisfied for all atoms.

Step-by-step solution

Calculate Valence Electrons

First, let's find the total number of valence electrons in borazine. In order to do so, we need to know the number of valence electrons for each element. Boron (B) has 3 valence electrons, Nitrogen (N) has 5 valence electrons, and Hydrogen (H) has 1 valence electron. Since there are 3 Boron, 3 Nitrogen, and 6 Hydrogen atoms in Borazine: Total valence electrons = (3 x 3) + (3 x 5) + (6 x 1) = 9 + 15 + 6 = 30.

Draw the Skeleton Structure

As mentioned, borazine contains a six-membered ring of alternating boron and nitrogen atoms, with hydrogen atoms bonded to boron and nitrogen. Start by drawing the ring of alternating B and N atoms, and then add the hydrogen atoms bonded to each B and N atom: ``` H | N---B---N | | B---N---B | H ```

Add the Electrons

Place the electrons around each atom, starting with the bonds between the atoms. Each bond in the molecule represents 2 shared electrons, so we've used 12 electrons for these 6 bonds. Now we need to add the 18 remaining electrons (30 total valence electrons - 12 used for bonds). Nitrogen atom requires 3 more electrons and hydrogen atom requires 1 more electron to fulfill the octet rule (2 electrons for hydrogen). We can add the remaining electrons to satisfy the octet rule for nitrogen atoms: ``` H | N = B - N | | B - N = B | H ```

Check the Octet Rule

Now that we have placed all the electrons in the structure, let's check if each atom follows the octet rule (2 electrons for hydrogen). Each nitrogen atom has 8 electrons around it, each boron atom has 6 electrons, and hydrogen atoms have 2 electrons. Since all atoms follow the octet rule, our Lewis structure is complete: ``` H | N = B - N | | B - N = B | H ``` This is the Lewis structure for borazine (B3N3H6).

Key concepts

Valence Electrons

Understanding valence electrons is crucial when constructing a Lewis structure. Valence electrons are the outermost electrons of an atom and are essential in determining how an atom bonds with others. For borazine \(\left(\mathrm{B}_{3} \mathrm{N}_{3} \mathrm{H}_{6}\right)\), we calculate the total number of valence electrons as follows:

• Boron (B) contributes 3 valence electrons per atom.
• Nitrogen (N) contributes 5 valence electrons per atom.
• Hydrogen (H) contributes 1 valence electron per atom.

Given that borazine has 3 boron atoms, 3 nitrogen atoms, and 6 hydrogen atoms, the total number of valence electrons is calculated by \((3 \times 3) + (3 \times 5) + (6 \times 1) = 30\) electrons. This total helps us arrange these electrons to achieve stable bonding configurations in the Lewis structure.

Octet Rule

The octet rule is a guideline that atoms tend to follow when forming compounds, aiming to complete their valence shell with 8 electrons (or 2 in the case of hydrogen). In borazine, our goal is to distribute the available valence electrons in a way that satisfies this rule, especially for the nitrogen and boron atoms. Each nitrogen atom seeks to be surrounded by 8 electrons to satisfy the octet rule. Boron, however, is an exception as it can be stable with only 6 electrons. Here’s how we apply the octet rule in borazine:

• Boron, being electron-deficient, accommodates 6 electrons.
• Nitrogen is provided with a full octet by sharing electrons with adjacent atoms.
• Hydrogen, needing only 2 electrons, achieves a duet by sharing with either boron or nitrogen.

By achieving these configurations, borazine forms a stable ring structure with alternating single and double bonds, ensuring that electron distribution is optimal for each element within the molecule.

Inorganic Benzene

Borazine is often termed "inorganic benzene" due to its structural resemblance to benzene—a well-known organic compound. Like benzene, borazine features a six-membered ring; however, instead of carbon atoms, the ring consists of alternating boron and nitrogen atoms. This similarity extends beyond structure:

• Both compounds exhibit resonance, although the electrons in borazine are distributed differently due to boron's electron deficiency and nitrogen's electron richness.
• In borazine, these alternating atoms contribute to delocalized electron circuits, stabilizing the molecule similar to aromatic systems found in organic chemistry.
• Even with these differences, borazine flouts conventional organic rules, merging the domains of inorganic and organic chemistry through its unique bonding patterns and resonance stabilization.

These features make borazine an interesting compound for study, offering insights into chemical bonding and the versatility of Lewis structures in describing complex molecules.