For each of the given species:
a. Draw its Lewis structure.
b. Describe the orbitals used by each carbon atom in bonding and indicate the approximate bond angles.
2. HCN

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Step 1: Draw the Lewis structure for HCN. Start by identifying the total number of valence electrons. Hydrogen (H) has 1 valence electron, carbon (C) has 4 valence electrons, and nitrogen (N) has 5 valence electrons. Add these together to get the total number of valence electrons.

Step 2: Arrange the atoms. Carbon (C) is the central atom because it can form the most bonds. Place hydrogen (H) and nitrogen (N) on either side of the carbon atom. Connect the atoms with single bonds initially.

Step 3: Distribute the remaining valence electrons to satisfy the octet rule. Start by completing the octet for nitrogen (N) and then adjust the bonding to ensure all atoms have a full valence shell. This will involve forming a triple bond between carbon (C) and nitrogen (N). Hydrogen (H) only needs 2 electrons to complete its shell.

Step 4: Describe the orbitals used by each carbon atom in bonding. Carbon in HCN forms a triple bond with nitrogen and a single bond with hydrogen. The carbon atom uses sp hybrid orbitals for bonding. One sp orbital overlaps with the 1s orbital of hydrogen, and the other sp orbital overlaps with an sp orbital of nitrogen. The remaining unhybridized p orbitals on carbon and nitrogen form two π bonds.

Step 5: Indicate the approximate bond angles. Since the carbon atom is sp hybridized, the molecule adopts a linear geometry. The bond angle between H-C-N is approximately 180°.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Lewis Structures

Lewis structures are diagrams that represent the bonding between atoms in a molecule and the lone pairs of electrons that may exist. They use dots to represent valence electrons and lines to represent bonds between atoms. Understanding how to draw Lewis structures is essential for visualizing molecular geometry and predicting the behavior of molecules in chemical reactions.

Hybridization

Hybridization is the concept of mixing atomic orbitals to form new hybrid orbitals that are suitable for the pairing of electrons to form chemical bonds. In the case of HCN, the carbon atom undergoes sp hybridization, which involves the mixing of one s orbital and one p orbital, resulting in two equivalent sp hybrid orbitals that are oriented linearly, leading to a bond angle of approximately 180 degrees.

Bond Angles

Bond angles are the angles formed between adjacent bonds in a molecule, which are influenced by the arrangement of electron pairs around the central atom. In HCN, the linear arrangement due to sp hybridization results in a bond angle of 180 degrees. Understanding bond angles is crucial for predicting the shape and reactivity of molecules based on VSEPR theory.

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