Problem 50 - Chemistry: Principles and Reactions

Question

A molecule of ethylamine is made up of two carbon atoms, seven hydrogen atoms, and one nitrogen atom. (a) Write its molecular formula. (b) The reactive group in ethylamine is \(\mathrm{NH}_{2}\). Write its condensed structural formula.

Step-by-Step Solution

Answer

Answer: The molecular formula of ethylamine is C₂H₇N, and the condensed structural formula is CH₃CH₂NH₂.

Step 1: Determine the Molecular Formula

Based on the information given in the exercise, we determine the molecular formula by listing the total number of atoms of each element present in the molecule. Since ethylamine consists of two carbon atoms, seven hydrogen atoms, and one nitrogen atom, its molecular formula can be represented as \(\mathrm{C}_{2}\mathrm{H}_{7}\mathrm{N}\). (a) The molecular formula of ethylamine is \(\mathrm{C}_{2}\mathrm{H}_{7}\mathrm{N}\).

Step 2: Determine the Condensed Structural Formula

To represent the condensed structural formula, we need to connect the atoms in the molecule, keeping in mind the reactive group \(\mathrm{NH}_{2}\). Ethylamine consists of two carbon atoms which are bonded as an ethyl group (with single bonds) with attached hydrogen atoms. The first carbon atom is bonded to three hydrogen atoms, and the second carbon atom is bonded to two hydrogen atoms. The nitrogen atom in the reactive group \(\mathrm{NH}_{2}\) is attached to the second carbon atom in the ethyl group, with two hydrogen atoms bonded to it. The condensed structural formula can be written as follows: \(\mathrm{CH}_{3}\mathrm{CH}_{2}\mathrm{NH}_{2}\) (b) The condensed structural formula of ethylamine is \(\mathrm{CH}_{3}\mathrm{CH}_{2}\mathrm{NH}_{2}\).

Key Concepts

Molecular Formula

Understanding the molecular formula of a compound like ethylamine is crucial for knowing the exact number of each type of atom present in the molecule. In chemistry, the molecular formula is a concise way of expressing information about the atoms that constitute a particular chemical compound. For ethylamine, the molecular formula is denoted as \( \mathrm{C}_{2}\mathrm{H}_{7}\mathrm{N} \). This formula tells us that the molecule consists of:

• Two carbon atoms (C)
• Seven hydrogen atoms (H)
• One nitrogen atom (N)

This notation is simple yet informative, as it provides a direct insight into the elemental composition of ethylamine. Each subscript number in the formula indicates the quantity of the respective atoms in a single molecule of ethylamine. By understanding the molecular formula, we can easily distinguish the structure and properties that differentiate ethylamine from other compounds.

Condensed Structural Formula

The condensed structural formula of ethylamine provides a bit more detail about the arrangement of atoms within the molecule. Unlike the molecular formula, which gives us the count of each type of atom, the condensed structural formula shows us how those atoms are connected. For ethylamine, the condensed structural formula is \( \mathrm{CH}_{3}\mathrm{CH}_{2}\mathrm{NH}_{2} \). Let's break this down:
The chain of carbon atoms is represented by \( \mathrm{CH}_{3}\mathrm{CH}_{2} \).

• \( \mathrm{CH}_{3} \) indicates that the first carbon atom is bonded to three hydrogen atoms.
• \( \mathrm{CH}_{2} \) signifies that the next carbon atom is connected to two hydrogen atoms.

Following this ethyl group is the nitrogen atom, denoted by \( \mathrm{NH}_{2} \), where the nitrogen is bonded to two hydrogen atoms. This sequence of symbols reflects the linear structural organization of ethylamine, allowing us to understand not only the elements present but also how they link together in 2D form.

Reactive Group NH2

The reactive group \( \mathrm{NH}_{2} \) in ethylamine is a fundamental feature that dictates much of the chemical behavior of the molecule. Known as the amino group, \( \mathrm{NH}_{2} \) is characterized by its nitrogen atom, which is bonded to two hydrogen atoms. This group is pivotal in ethylamine's reactivity for several reasons:

• It can act as a base, accepting protons from other molecules due to the lone pair of electrons on the nitrogen atom.
• It participates in hydrogen bonding, affecting the solubility and boiling point of ethylamine.
• The amino group positions ethylamine within the category of primary amines, which are notable for their applications in various chemical syntheses.

Understanding the reactive group \( \mathrm{NH}_{2} \) is essential because it plays a crucial role in the interactions that ethylamine can participate in, either as a solvent in chemical processes or as a reactant in forming new compounds.