Question

Write the electron dot formula and draw the structural formula for each of the following molecules: (a) HONO (b) SO \(_{2}\) (c) \(\mathrm{C}_{2} \mathrm{H}_{4}\) (d) \(\mathrm{C}_{2} \mathrm{H}_{2}\)

Short answer

HONO: H-O-N=O with extra lone pairs; SO2: O=S=O; C2H4: H2C=CH2; C2H2: H-C≡C-H.

Step-by-step solution

HONO - Determine Total Valence Electrons

HONO consists of H (1 electron), O (6 electrons), N (5 electrons), and another O (6 electrons), totaling to 18 valence electrons. The formula for adding them is: \(1 + 6 + 5 + 6 = 18\).

HONO - Draw Skeletal Structure

In HONO, H is attached to O, which is then connected to N, and finally to another O. The skeletal structure is H-O-N=O. Hydrogen needs only one bond, and nitrogen often forms three bonds. The oxygen double-bonded to nitrogen needs a double bond to fulfill its octet.

HONO - Distribute Remaining Electrons

With single bonds connecting oxygen to hydrogen and nitrogen, and a double bond between nitrogen and the second oxygen, assign remaining electron pairs to satisfy the octet for each oxygen and nitrogen atom. Place any unused electrons as lone pairs on oxygen atoms.

SO2 - Determine Total Valence Electrons

SO\(_2\) consists of S (6 electrons) and O (6 electrons each). There are two oxygen atoms, so: \(6 + 6\times2 = 18\) total valence electrons.

SO2 - Draw Skeletal Structure

For SO\(_2\), sulfur is central, bonded with single bonds to each oxygen atom. Start with this basic structure to allocate bonds.

SO2 - Distribute and Balance Electrons

Sulfur forms one double bond with each oxygen to satisfy oxygen's octet. The final structure is bonded as O=S=O, and any leftover electrons are lone pairs on the oxygen atoms.

C2H4 - Determine Total Valence Electrons

C\(_2\)H\(_4\) has two carbons (2\times4 electrons) and four hydrogens (4\times1 electron). Thus, \(2\times4 + 4\times1 = 12\) total valence electrons.

C2H4 - Draw Skeletal Structure

Connect the two carbon atoms with a double bond and link each carbon to two hydrogen atoms with single bonds.

C2H2 - Determine Total Valence Electrons

C\(_2\)H\(_2\) consists of two carbons (2\times4 electrons) and two hydrogens (2\times1 electron), making \(2\times4 + 2\times1 = 10\) valence electrons.

C2H2 - Draw Skeletal Structure

For C\(\equiv\)C-H, connect carbon atoms with a triple bond, then attach one hydrogen to each carbon with a single bond.

Review and Correct

Examine each molecule's structure to ensure completeness (each atom's octet) and all valence electrons accounted. Adjust any errors found in electron counts or bond assignments.

Key concepts

Valence Electrons

Valence electrons are the outermost electrons in an atom and play a crucial role in chemical bonding. Understanding the number of valence electrons allows us to predict how atoms will interact and bond with each other. This is because valence electrons are involved in forming bonds between atoms in a molecule.

• To determine the number of valence electrons, we often refer to the periodic table. Each group in the periodic table represents elements with the same number of valence electrons.
• For instance, HONO has different atoms: hydrogen (1 valence electron), oxygen (6 valence electrons), and nitrogen (5 valence electrons).

This totals up to 18 valence electrons for HONO, guiding us in sketching the molecule's possible bonds. Knowing this helps create the foundation for developing molecular structures and predicting molecule geometry.

Molecular Structures

Molecular structures describe how atoms are connected and arranged within a molecule. They provide a three-dimensional context, indicating the spatial arrangement of atoms. Understanding molecular structures is essential for comprehending chemical reactions and properties.

• In a molecule like SO e2 e, the structure O=S=O indicates that sulfur and oxygen atoms are double-bonded. This structural representation gives us insight into how the molecule might interact with others.
• C e2 eH e4 e (ethylene) has a central carbon double bond and is connected to hydrogen atoms, forming a planar structure.

These structural insights help you see beyond the dots and lines of basic drawings, allowing you to visualize how molecules are shaped and, therefore, how they might behave in different contexts or chemical reactions.

Lewis Structures

Lewis structures are diagrams that represent atoms and their valence electrons in a molecule. They provide a way to visualize the shared and unshared electrons, clarifying molecular structure and bonding patterns.

• The simple lines in Lewis structures represent bonding pairs of electrons, while dots around atoms denote lone pairs not involved in bonding.
• For example, HONO is described by connecting hydrogen and oxygen with a single bond, then linking oxygen to nitrogen, which is further bonded to another oxygen with a double bond.
• In this setup, unshared electrons on oxygen and nitrogen are shown as dots, fulfilling each atom's octet requirement, which stabilizes the molecule.

Lewis structures effectively summarize the electron distribution in molecules, helping us predict how different molecules might interact or change during chemical reactions.