Problem 93 - Chemistry The Central Science

Question

(a) Triazine, \(\mathrm{C}_{3} \mathrm{H}_{3} \mathrm{~N}_{3}\), is like benzene except that in triazine every other \(\mathrm{C}-\mathrm{H}\) group is replaced by a nitrogen atom. Draw the Lewis structure(s) for the triazine molecule. (b) Estimate the carbon-nitrogen bond distances in the ring.

Step-by-Step Solution

Answer

(a) The Lewis structure for Triazine can be drawn as: N // \\ C-----C || || H N **|** C **|** H (b) The estimated bond distances in the Triazine ring for carbon-nitrogen single bond and carbon-nitrogen double bond are approximately 1.47 Å and 1.32 Å, respectively.

Step 1: (a) Drawing the Lewis structure(s) for Triazine

Step 1: Count the total number of valence electrons. Triazine has 3 carbon (C) atoms, 3 hydrogen (H) atoms, and 3 nitrogen (N) atoms. The number of valence electrons in the molecule can be calculated as follows: - Carbon (C) has 4 valence electrons. So, for 3 carbon atoms, total valence electrons = 3 x 4 = 12. - Hydrogen (H) has 1 valence electron. So, for 3 hydrogen atoms, total valence electrons = 3 x 1 = 3. - Nitrogen (N) has 5 valence electrons. So, for 3 nitrogen atoms, total valence electrons = 3 x 5 = 15. Total valence electrons = 12 + 3 + 15 = 30 Step 2: Draw the central skeleton. Place carbon and nitrogen atoms alternatively in a hexagonal structure. N **|** C-----C | | H N **|** C **|** H Step 3: Arrange the valence electrons. Add lone pairs and bond pairs on atoms to make sure each carbon atom has 8 electrons, hydrogen atoms have 2 electrons, and nitrogen atoms have 8 electrons as well. N // \\ C-----C || || H N **|** C **|** H Repeat the process for other possible Lewis structures of Triazine.

Step 2: (b) Estimating the carbon-nitrogen bond distances in the ring

To estimate the carbon-nitrogen bond distances in the ring, we can refer to the standard bond lengths of carbon-nitrogen single bonds, carbon-nitrogen double bonds, and carbon-nitrogen triple bonds. In the Lewis structure for Triazine, we have a carbon-nitrogen single bond and a carbon-nitrogen double bond. The average bond lengths for C-N single bond and C-N double bond are as follows: - The average bond length for a C-N single bond: \( \approx 1.47\) Å (Angstrom) - The average bond length for a C-N double bond: \( \approx 1.32\) Å (Angstrom) Thus, the estimated bond distances in the Triazine ring for C-N single bond and C-N double bond are approximately 1.47 Å and 1.32 Å, respectively.

Key Concepts

Valence Electrons

Valence electrons are the electrons in the outermost shell of an atom that are involved in forming bonds with other atoms. In the case of triazine (C₃H₃N₃), we must first tally these electrons before drawing the molecule's Lewis structure. Carbon with 4, hydrogen with 1, and nitrogen with 5 valence electrons contribute to the molecule's overall valence electron count.

To determine the total valence electron count in triazine, we calculate it as: (3 carbons x 4) + (3 hydrogens x 1) + (3 nitrogens x 5) = 30 valence electrons. These electrons will be distributed around the atoms to satisfy the octet rule for carbon and nitrogen, and the duet rule for hydrogen, establishing the structure of the molecule. Understanding the distribution of valence electrons is crucial in predicting the chemical properties and reactivity of the molecule.

Chemical Bonding

Chemical bonding is the process by which atoms combine to form molecules. The Lewis structure of triazine illustrates how atoms bond using their valence electrons. In triazine, each carbon and nitrogen atom must be surrounded by eight electrons to fulfill the octet rule, forming a stable configuration, while each hydrogen atom should have two electrons to fulfill the duet rule.

In our Lewis structure, alternating carbon and nitrogen atoms create bonds that ensure the octet rule is satisfied. Carbon atoms share electrons with both nitrogen and hydrogen atoms. In contrast, the nitrogen atoms only share electrons with carbon. The specific arrangement of single and double bonds is critical, as it influences the molecule's overall stability and reactivity.

Molecular Geometry

Molecular geometry refers to the shape of a molecule determined by the spatial arrangement of its atoms. Once the Lewis structure of triazine is drawn, we can infer its geometry. The molecule has a hexagonal ring structure with alternating carbon and nitrogen atoms. The geometry around each carbon and nitrogen atom in the ring is planar, due to the presence of sp² hybridized orbitals, characteristic of such arrangements.

The molecular geometry not only defines the shape but also affects the molecule's physical and chemical properties, like reactivity, polarity, and interaction with other molecules. In triazine, bond angles are approximately 120 degrees, which is typical for planar hexagonal structures, and the molecule's symmetry contributes to its unique characteristics.