Problem 11 - Chemistry

Question

Draw an electron-dot structure for the following molecules or ions: (a) Methylamine, \(\mathrm{CH}_{5} \mathrm{~N}\) (b) Ethylene, \(\mathrm{C}_{2} \mathrm{H}\) (c) Propane, \(\mathrm{C}_{3} \mathrm{H}_{8}\) (d) Hydrogen Peroxide, \(\mathrm{H}_{2} \mathrm{O}_{2}\) (e) Hydrazine, \(\mathrm{N}_{2} \mathrm{H}_{4}\)

Step-by-Step Solution

Answer

These structures represent connections and lone pairs in methylamine, ethylene, propane, hydrogen peroxide, and hydrazine, accurately capturing their configurations.

Step 1: Methylamine Structure

Methylamine (CH_{5} N) consists of 1 nitrogen atom, 1 carbon atom, and 5 hydrogen atoms. Begin by writing carbon bonded to nitrogen, then attach three hydrogens to carbon and two hydrogens to nitrogen. Note that nitrogen will have one lone pair. \[\begingroup \renewcommand{\arraystretch}{1.2} \begin{array}{cccccc} \: & \: & H & \: & \: & \: \ \: & \: & | & \: & \: & \: \ H - & C & - N & - H & \: & \: \ \: & | & : & \: & \: & \: \ \: & H & \: & \: & \: & \: \ \end{array}\endgroup\]

Step 2: Ethylene Structure

Ethylene (C_2 H_4) is composed of two carbon atoms double-bonded to each other. Attach two hydrogen atoms to each carbon atom. \[\begin{array}{ccccc} H & \: & H & \: & H \ | & \: & | & \: & | \ C = & C & - & \: & H \ | & \: & | & \: & \: \ H & \: & H & \: & \: \\end{array}\]

Step 3: Propane Structure

Propane (C_3 H_8) involves a chain of three carbon atoms, each with enough hydrogen atoms to fulfill the octet rule. Begin by linking three carbon atoms, then add enough hydrogens to each central carbon to provide each atom with four bonds. \[\begin{array}{ccccc} H & & H & & H \ | & & | & & | \ H - \: & C & - C & - \: & C - H \ | & & | & & | \ H & & H & & H \\end{array}\]

Step 4: Hydrogen Peroxide Structure

Hydrogen Peroxide (H_2 O_2) has two oxygen atoms connected by a single bond, with each oxygen also bonded to a hydrogen atom. Each oxygen will have two lone pairs. \[\begin{array}{ccccc} H & \: & O & : & \: \ | & \: & | & \: & \: \ \bullet & \rightarrow & \bullet & \leftarrow & \bullet \ | & \: & | & \: & \: \ H & \: & O & : & \: \\end{array}\]

Step 5: Hydrazine Structure

Hydrazine (N_2 H_4) features two nitrogen atoms connected by a single bond, with each nitrogen bonded to two hydrogen atoms. Both nitrogen atoms have one lone pair. \[\begin{array}{ccccc} H & & H & & H \ | & & | & & | \ N & - & N & - & H \ : & & : & & : \ H & & H & & : \\end{array}\]

Step 6: Conclusion

Each molecule or ion uses the appropriate number of bonds between atoms following the basic rules of electron-dot structures, such as satisfying the octet rule and accounting for pairs and lone pairs of electrons.

Key Concepts

Methylamine

Methylamine, represented as \(\text{CH}_5\text{N}\), is a simple molecule made up of carbon, hydrogen, and nitrogen atoms. When drawing the electron-dot structure for methylamine, we focus on the connectivity of these atoms:
- **Carbon (C)** typically forms four bonds, here it bonds with nitrogen and three hydrogen atoms.
- **Nitrogen (N)** generally forms three bonds and carries a lone pair of electrons in this molecule.
- In methylamine, nitrogen is bonded to carbon and two hydrogens. Thus, the nitrogen completes its octet with one lone pair.
- Each hydrogen atom shares a single electron with either carbon or nitrogen to achieve a full valence shell.

This structure illustrates the shared electron pairs (bonds) between atoms and highlights nitrogen's lone pair, which is crucial for the molecule’s basicity.

Ethylene

Ethylene, or \(\text{C}_2\text{H}_4\), is an organic compound made of two carbon atoms double-bonded to each other. To visualize its electron-dot structure, consider the following:
- **Carbon (C)** forms four bonds in total, two of which are used to form a double bond between the carbon atoms.
- Each carbon then forms two single bonds with hydrogen atoms, resulting in each carbon atom having a stable electron configuration.
- This compound is planar, and the double bond restricts the rotation, hence the reason for ethylene’s rigid structure.

This electron-dot representation emphasizes the double bond formed by sharing two pairs of electrons between the carbon atoms, resulting in a stable, basic organic structure.

Propane

Propane, designated as \(\text{C}_3\text{H}_8\), is a hydrocarbon that consists of a three-carbon chain. In its electron-dot structure, the connectivity and saturation of bonds are essential:
- **Carbon (C)** atoms are connected in a straight chain, with each carbon atom making four single bonds to satisfy its tetravalent nature.
- The terminal carbon atoms connect to three hydrogen atoms each, while the middle carbon binds to two hydrogen atoms.
- This setup ensures that all carbon atoms meet the octet rule, each forming four bonds that keep the molecule stable.

Propane’s electron-dot structure highlights its saturated nature, showing it is fully single-bonded and forms a simple linear alkane.

Hydrogen Peroxide

Hydrogen peroxide, with the formula \(\text{H}_2\text{O}_2\), consists of two oxygen atoms connected by a single bond. Understanding its electron-dot structure involves:
- **Oxygen (O)** naturally forms two bonds and often has two lone pairs to complete its typical six valence electrons.
- In hydrogen peroxide, each oxygen atom is bonded to one hydrogen atom through a single bond.
- The two oxygen atoms are linked together, creating an O-O single bond, with both oxygen atoms featuring two lone pairs, enhancing their stability.

This structure serves to display how hydrogen peroxide balances shared electrons in bonds while maintaining the key non-bonded lone pairs, which are significant for its reactive properties.

Hydrazine

Hydrazine, represented by \(\text{N}_2\text{H}_4\), is composed of nitrogen and hydrogen atoms. Visualizing its electron-dot structure means acknowledging:
- **Nitrogen (N)** atoms form three bonds and typically have one lone pair to satisfy their six valence electrons.
- The two nitrogen atoms connect via a single bond, with each nitrogen bonded to two hydrogen atoms.
- Each nitrogen atom completes its electron octet with a lone pair, which illustrates hydrazine’s tendency to donate or accept hydrogen bonds.

In hydrazine's electron-dot structure, the presence of nitrogen's lone pair is crucial, as it plays a role in the compound’s reactivity and polarity. This dual-lone pair setup additionally influences its ability to engage in various chemical reactions.