Question

Draw Lewis structures for the following organic molecules: \(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{~F}, \mathrm{C}_{3} \mathrm{H}_{6}, \mathrm{C}_{4} \mathrm{H}_{8} .\) In each there is one \(\mathrm{C}=\mathrm{C}\) bond, and the rest of the carbon atoms are joined by \(\mathrm{C}-\mathrm{C}\) bonds.

Short answer

C₂H₃F, C₃H₆, and C₄H₈ have one C=C bond, rest are C-C bonds, satisfying all valence rules.

Step-by-step solution

Identify Valence Electrons

Determine the total number of valence electrons for each molecule. Carbon (C) has 4 valence electrons, hydrogen (H) has 1, and fluorine (F) has 7. Calculate the total for each molecule: - C₂H₃F: 2(4) + 3(1) + 7 = 18 electrons - C₃H₆: 3(4) + 6(1) = 18 electrons - C₄H₈: 4(4) + 8(1) = 24 electrons

Draw the Skeleton Structure

Lay out the basic structure of each molecule, keeping in mind the given constraint that each molecule must contain one C=C bond: - C₂H₃F: Start with a C=C bond; attach H atoms and F atom to complete the structure. - C₃H₆: Have a C=C bond in the middle, with C atoms on either side, and distribute H atoms around. - C₄H₈: Similar to C₃H₆ but with two additional carbon chains off the C=C center.

Distribute Remaining Electrons

Distribute the remaining electrons as lone pairs, giving fluorine a complete octet first: - C₂H₃F: Place lone pairs on F to make 8 electrons around it. - C₃H₆: No lone pairs needed since H only needs 2 electrons and C is satisfied with 4 covalent bonds. - C₄H₈: Similar approach as C₃H₆; ensure each C has 4 bonds.

Check for Octet Completion

Ensure each carbon atom forms 4 bonds, and confirm each hydrogen forms 1 bond. Fluorine should have a complete octet. - Double-check that all atoms adhere to the octet rule (except for hydrogen).

Key concepts

Valence Electrons

Valence electrons are the outermost electrons in an atom and are crucial for bonding in molecules. They are the electrons that participate in forming chemical bonds, and they largely determine the chemical properties of an element.
For organic molecules, understanding the number of valence electrons is key to drawing Lewis structures.

• Carbon (C) has 4 valence electrons.
• Hydrogen (H) has 1 valence electron.
• Fluorine (F) has 7 valence electrons.

When drawing a Lewis structure, first calculate the total number of valence electrons for the molecule. This helps determine how these electrons can be shared among the atoms to form stable compounds.

Organic Molecules

Organic molecules are compounds mainly composed of carbon atoms linked together, usually with hydrogen, oxygen, and other elements attached.
These molecules form the basis of life on Earth, with structures that can be very simple or incredibly complex.

• Carbon's ability to form four bonds allows for a wide diversity of organic structures.
• In organic molecules, the arrangement of atoms determines the molecule's chemical properties and behaviors.
The molecules like C₂H₃F, C₃H₆, and C₄H₈ each demonstrate unique characteristics based on their structure, with carbon-carbon double bonds influencing their reactivity and interactions.

C=C Bond

The carbon-carbon double bond is denoted as C=C and plays a vital role in organic chemistry.
This type of bond involves the sharing of two pairs of valence electrons, resulting in a stronger, shorter bond compared to a single bond.

• Double bonds affect the shape and geometry of the molecule, causing a planar arrangement around the bonded carbons.
• The C=C bond is critical for functionalities and reactions, determining aspects like rigidity and the molecule's ability to rotate.

In our molecules, the presence of a C=C bond adds specific constraints and properties, defining their structural layout and reactivity.

Octet Rule

The octet rule is a guiding principle in chemistry that helps predict the formation and structure of molecules.
It states that atoms tend to form bonds such that each atom has an octet of electrons in its outer shell, achieving a stable configuration like the noble gases.

• For carbon in organic molecules, this usually means forming 4 bonds.
• Hydrogen is an exception and is stable with 2 electrons, forming just one bond.
• Fluorine, with 7 valence electrons, typically forms one bond and possesses three lone pairs to complete its octet.

Each molecule should be checked against the octet rule to ensure stability, providing a useful framework for drawing correct Lewis structures.