Write Lewis structures for the following molecular formulas. Circle any lone pairs (pairs of nonbonding electrons) in the structures.
i. C₃H₆ (one double bond)
j. C₃H₄ (two double bonds)
k. C₃H₄ (one triple bond)

Verified step by step guidance

1. Identify the total number of valence electrons for each molecule. For C3H6, C3H4 (two double bonds), and C3H4 (one triple bond), calculate the sum of valence electrons from carbon and hydrogen atoms.
2. For C3H6, arrange the carbon atoms in a chain and add a double bond between two of the carbon atoms. Distribute the remaining hydrogen atoms around the carbon atoms to satisfy the valency of carbon (four bonds per carbon atom).
3. For C3H4 with two double bonds, arrange the carbon atoms in a linear or branched structure. Introduce two double bonds between the carbon atoms. Distribute the hydrogen atoms to satisfy the valency of carbon.
4. For C3H4 with one triple bond, arrange the carbon atoms in a linear structure. Introduce a triple bond between two carbon atoms and a single bond between the remaining carbon atom and one of the triple-bonded carbons. Distribute the hydrogen atoms to satisfy the valency of carbon.
5. Circle any lone pairs of electrons on the carbon atoms, if present, after ensuring that all atoms have satisfied their valency. Typically, in these hydrocarbons, there are no lone pairs on carbon, but ensure all hydrogen atoms are bonded and all carbon atoms have four bonds.

Key Concepts

Lewis Structures

Lewis structures are diagrams that represent the bonding between atoms of a molecule and the lone pairs of electrons that may exist. They are essential for visualizing the arrangement of atoms, the distribution of electrons, and the types of bonds (single, double, or triple) present in a molecule. Understanding how to draw Lewis structures helps in predicting molecular geometry, reactivity, and properties.

Double and Triple Bonds

Double and triple bonds are types of covalent bonds where two or three pairs of electrons are shared between two atoms, respectively. A double bond consists of one sigma and one pi bond, while a triple bond consists of one sigma and two pi bonds. These bonds affect the molecule's geometry and reactivity, with triple bonds being shorter and stronger than double bonds.

Lone Pairs

Lone pairs are pairs of valence electrons that are not involved in bonding and belong exclusively to one atom. In Lewis structures, they are represented as pairs of dots around the atom. Lone pairs can influence the shape and polarity of a molecule, as they occupy space and can repel bonding pairs, affecting bond angles and molecular geometry.