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Ch.10 - Chemical Bonding I: The Lewis Model
All textbooksTro 6th EditionCh.10 - Chemical Bonding I: The Lewis ModelProblem 98
Chapter 10, Problem 98

Diazomethane is a highly poisonous, explosive compound because it readily evolves N2. Diazomethane has the following composition by mass: 28.57% C; 4.80% H; and 66.64% N. The molar mass of diazomethane is 42.04 g/mol. Find the molecular formula of diazomethane, draw its Lewis structure, and assign formal charges to each atom. Why is diazomethane not very stable? Explain.

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Calculate the moles of each element in a 100 g sample of diazomethane. Use the given mass percentages: 28.57% C, 4.80% H, and 66.64% N. Convert these percentages to grams: 28.57 g C, 4.80 g H, and 66.64 g N. Then, divide each by the atomic mass of the respective element to find the moles: C (12.01 g/mol), H (1.008 g/mol), N (14.01 g/mol).
Determine the empirical formula by finding the simplest whole number ratio of moles of each element. Divide the moles of each element by the smallest number of moles calculated in step 1.
Calculate the empirical formula mass by adding the atomic masses of the elements in the empirical formula. Compare this mass to the given molar mass of diazomethane (42.04 g/mol) to find the ratio between the molecular and empirical formula masses.
Multiply the subscripts in the empirical formula by the ratio found in step 3 to determine the molecular formula of diazomethane.
Draw the Lewis structure of diazomethane using the molecular formula. Assign formal charges to each atom by using the formula: Formal charge = (Valence electrons) - (Non-bonding electrons) - 0.5*(Bonding electrons). Discuss the stability of diazomethane by considering the presence of any formal charges and the tendency of the compound to release N2 gas.>

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Molecular Formula Determination

The molecular formula of a compound indicates the types and numbers of atoms present. To determine it, one must convert the percentage composition by mass into moles for each element, then find the simplest whole-number ratio of these moles. In the case of diazomethane, the given mass percentages can be used to calculate the number of moles of carbon, hydrogen, and nitrogen, leading to the identification of its molecular formula.
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Lewis Structures

A Lewis structure is a diagram that represents the bonding between atoms in a molecule and the lone pairs of electrons. It helps visualize how atoms are connected and the distribution of electrons. Drawing the Lewis structure for diazomethane involves placing the atoms in a way that satisfies the octet rule where applicable, and accurately depicting the bonds and lone pairs, which is crucial for understanding the molecule's reactivity and stability.
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Stability and Formal Charges

The stability of a molecule is influenced by the arrangement of electrons and the presence of formal charges. Formal charge is calculated based on the difference between the number of valence electrons an atom has and the number it is assigned in the Lewis structure. In diazomethane, the presence of formal charges can indicate potential instability, as molecules tend to be more stable when formal charges are minimized or distributed evenly across atoms.
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Related Practice
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