Draw Lewis structures for the following organic molecules: (a) tetrafluoroethylene \(\left(\mathrm{C}_{2} \mathrm{~F}_{4}\right),\) (b) propane \(\left(\mathrm{C}_{3} \mathrm{H}_{8}\right),(\mathrm{c})\) butadiene \(\left(\mathrm{CH}_{2} \mathrm{CHCHCH}_{2}\right),\) (d) propyne \(\left(\mathrm{CH}_{3} \mathrm{CCH}\right),(\mathrm{e})\) benzoic acid \(\left(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COOH}\right) .\) (To draw \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COOH},\) replace a \(\mathrm{H}\) atom in benzene with a COOH group.)

Understanding valence electrons is crucial when drawing Lewis structures for organic molecules. Valence electrons are the electrons in the outermost shell of an atom that are involved in forming bonds. Each atom has a characteristic number of valence electrons that can participate in bonding.

In organic chemistry, carbon is a key element and has four valence electrons. Hydrogen, with one valence electron, often forms bonds with carbon. Other common atoms in organic molecules include oxygen with six valence electrons, nitrogen with five, and halogens like fluorine with seven.

Calculating Total Valence Electrons

To determine the total number of valence electrons in a molecule, simply multiply the number of valence electrons for each type of atom by the number of atoms of that type in the molecule, then sum the results. This total guides you in drawing an accurate Lewis structure, ensuring that all atoms achieve a stable configuration while maintaining the conservation of electrons.

The skeletal structure acts as the backbone of the Lewis structure in organic molecules. It's a simplified representation showing the layout of atoms in a molecule without depicting all the valence electrons.

Steps for Creating a Skeletal Structure

• Identify the central atoms, which are usually carbon atoms in organic molecules.
• Connect the central atoms with single lines, each representing a pair of shared electrons — a single bond.
• Attach hydrogen and halogen atoms to the carbon skeleton, as they are usually terminal (at the ends of the structure).
• Remember that hydrogen and halogens have one connection point, while oxygen typically has two, and nitrogen three.

By drawing the skeletal structure, you create a visual outline that leads to a more detailed Lewis structure, which will include all valence electrons and depict the electron sharing or transferring that creates chemical bonds. This step is especially helpful for visually understanding complex organic structures.

After drawing the skeletal structure, the next step is to fill the octets for each atom in the molecule. The 'octet rule' states that atoms strive to have eight electrons in their outer shell, similar to noble gases, which are naturally stable.

Tips to Complete Octets

• Place pairs of electrons around each atom, starting with the terminal atoms (except for hydrogen, which is satisfied with two electrons).
• After assigning electrons to the terminal atoms, move inward, placing the remaining electrons around the central atoms.
• Ensure that carbon and other atoms that follow the octet rule achieve eight electrons in their valence shell.
• Double or triple bonds may form between atoms if there are not enough electrons to complete octets with single bonds alone.

Completing octets correctly is pivotal in portraying the stability of the molecule and its reactive sites. Lewis structures enable a visual confirmation that all atoms have reached an optimal electronic configuration, key to predicting molecular properties and reactivity.

Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. In Lewis structures, they are represented by particular arrangements of atoms and associated electrons.

Identifying Common Functional Groups

• Hydroxyl (-OH): consists of an oxygen and hydrogen atom; indicative of alcohols.
• Carbonyl (>C=O): a double bond between a carbon and an oxygen atom; found in aldehydes and ketones.
• Carboxyl (-COOH): a combination of hydroxyl and carbonyl groups; characteristic of carboxylic acids.
• Amine (-NH2): composed of a nitrogen atom bound to hydrogen atoms or carbon; present in amino acids.

In a Lewis structure, these functional groups are represented by showing their bonds and the arrangement of their atoms, adhering to the octet rule. Understanding how to represent functional groups in Lewis structures is important for recognizing how organic molecules interact and the reactions they may undergo.