Question

Use VSEPR to predict bond angles about each atom of carbon, nitrogen, and oxygen in these molecules. a. b. c. d. e. f.

Short answer

Question: Predict the bond angles around the carbon, nitrogen, and oxygen atoms in a given molecule using the VSEPR theory. Answer: To predict bond angles, follow the steps outlined in the provided solution: Determine the electronic geometry of the atom, deduce the VSEPR notation, identify the molecular shape, and determine the corresponding bond angles for that shape. Once you know the bond angles, you can compare them for the carbon, nitrogen, and oxygen atoms in your specific molecule.

Step-by-step solution

Determine the electronic geometry of the atom

To predict bond angles, we first need to know the electronic geometry associated with the central atom. In this case, we will analyze carbon, nitrogen, and oxygen atoms. Each atom has a specific number of valence electrons (carbon has 4, nitrogen has 5, and oxygen has 6). You need to determine the total number of valence electrons around the atom, considering any shared electrons from bonds.

Deduce the VSEPR notation

Based on the number of bonding electron pairs and lone electron pairs surrounding the atom, deduce the VSEPR notation. The notation follows the format AXnEm, where A is the central atom, Xn represents the number of bonded atoms (n), and Em represents the number of lone pairs (m).

Identify the molecular shape

Using the VSEPR notation, identify the shape of the molecule which is directly associated with the atom. Common shapes include linear, trigonal planar, tetrahedral, trigonal bipyramidal, and octahedral.

Determine the bond angles

Finally, determine the bond angles that correspond to the molecular shape you identified in step 3. The bond angles will vary based on the number of bonding and lone electron pairs around the central atom. Here are some general bond angles for common shapes: - Linear: 180° - Trigonal planar: 120° - Tetrahedral: 109.5° - Trigonal bipyramidal: 90° and 120° - Octahedral: 90° Keep in mind that lone pairs can affect bond angles slightly, causing them to be slightly smaller than the typical angles listed above. Once you have determined the bond angles for the atom, you can then compare them to the atoms in your specific molecules.

Key concepts

Bond Angles

Bond angles refer to the angle formed between two adjacent bonds coming from the same atom. These angles are crucial in defining the shape and properties of a molecule. In the VSEPR (Valence Shell Electron Pair Repulsion) theory, bond angles are determined by the repulsion between electron pairs around a central atom.

To predict bond angles, consider the type of molecular geometry. For example, a linear geometry has bond angles of 180°, while a tetrahedral geometry has angles of 109.5°. These angles can change when there are lone pairs present as they repel more strongly than bonding pairs, slightly reducing the angles between bonding atoms.

Molecular Geometry

Molecular geometry describes the three-dimensional arrangement of atoms within a molecule. This arrangement is determined by the number of bonding pairs and lone pairs around a central atom, based on VSEPR theory.

Common molecular geometries include:

• Linear: Atoms are arranged in a straight line.
• Trigonal Planar: Three atoms are arranged around a central atom in a plane forming 120° bond angles.
• Tetrahedral: Four atoms form bond angles of 109.5° with respect to each other around a central atom.
• Bent: The geometry is altered by lone pairs, resulting in angles less than 120° or 109.5° depending on the molecule.

Understanding molecular geometry helps explain the physical and chemical properties of a substance.

Lone Pairs

Lone pairs are non-bonding pairs of electrons found in the outer shell of an atom. Unlike bonding pairs, lone pairs are not shared between atoms but belong exclusively to one atom. These pairs are crucial in shaping the geometry of a molecule through electron repulsion.

Lone pairs tend to repel bonding pairs more strongly, which can impact bond angles, often causing them to decrease from their ideal values. In a trigonal planar geometry, the presence of a lone pair would transform the shape into a bent geometry, reducing bond angles. Recognizing the influence of lone pairs helps in predicting and understanding molecular shapes more accurately.

Valence Electrons

Valence electrons are the electrons located in the outermost shell of an atom. These electrons play a pivotal role in chemical reactions and bond formation.

In VSEPR theory, counting valence electrons is the first step in predicting molecular geometry. For example:

• Carbon has 4 valence electrons, which can form up to 4 bonds.
• Nitrogen has 5 valence electrons, forming typically 3 bonds with a lone pair remaining.
• Oxygen has 6 valence electrons and usually forms 2 bonds with 2 lone pairs.

Understanding the number of valence electrons helps in drawing Lewis structures and deciding how atoms bond, highlighting the importance of these electrons in determining the shapes of molecules.