Question

Draw the Lewis structures for \(\mathrm{SO}_{2}, \mathrm{PCl}_{3}, \mathrm{NNO}, \mathrm{COS},\) and \(\mathrm{PF}_{3} .\) Which of the compounds are polar? Which of the compounds exhibit at least one bond angle that is approximately 120 degrees? Which of the compounds exhibit \(s p^{3}\) hybridization by the central atom? Which of the compounds have a linear molecular structure?

Short answer

The Lewis structures for the given molecules are: \(\mathrm{SO}_{2}\): O=S=O, \(\mathrm{PCl}_{3}\): P-Cl(3 times), \(\mathrm{NNO}\): N=N=O, \(\mathrm{COS}\): O=C=S, and \(\mathrm{PF}_{3}\): P-F(3 times). Polar molecules are \(\mathrm{SO}_{2}, \mathrm{COS}\), and \(\mathrm{NNO}\). The molecule with a bond angle of approximately 120 degrees is \(\mathrm{PCl}_{3}\). The molecule with sp^3 hybridization is \(\mathrm{PF}_{3}\). Linear molecules are \(\mathrm{SO}_{2}, \mathrm{NNO}\), and \(\mathrm{COS}\).

Step-by-step solution

Drawing the Lewis structures

For each molecule, follow these steps: 1. Count the total number of valence electrons. 2. Start with the central atom and place the remaining atoms around it. 3. Add single bonds between the central and surrounding atoms, and assign the remaining electrons as lone pairs. 4. If there are still electrons left, add double or triple bonds if necessary. 1. \(\mathrm{SO}_{2}\): Sulfur has 6 valence electrons, and oxygen has 6 valence electrons each. The total number of valence electrons is 18. Sulfur is the central atom, and the Lewis structure is as follows: O=S=O 2. \(\mathrm{PCl}_{3}\): Phosphorus has 5 valence electrons, and chlorine has 7 valence electrons each. The total number of valence electrons is 26. Phosphorus is the central atom, and the Lewis structure is as follows: Cl | P-Cl-Cl 3. \(\mathrm{NNO}\): Nitrogen has 5 valence electrons each, and oxygen has 6 valence electrons. The total number of valence electrons is 16. Nitrogen is the central atom, and the Lewis structure is as follows: N=N=O 4. \(\mathrm{COS}\): Carbon has 4 valence electrons, oxygen has 6 valence electrons, and sulfur has 6 valence electrons. The total number of valence electrons is 16. Carbon is the central atom, and the Lewis structure is as follows: O=C=S 5. \(\mathrm{PF}_{3}\): Phosphorus has 5 valence electrons, and fluorine has 7 valence electrons each. The total number of valence electrons is 26. Phosphorus is the central atom, and the Lewis structure is as follows: F | P-F-F

Identify polar molecules

Molecules are polar when their bond dipoles do not cancel each other out. In this case, \(\mathrm{SO}_{2}, \mathrm{COS}\) and \(\mathrm{NNO}\) are polar molecules due to their asymmetric distribution of electrons.

Find molecules with a bond angle of approximately 120 degrees

Molecules with trigonal planar geometry have bond angles of approximately 120 degrees. In this case, only \(\mathrm{PCl}_{3}\) exhibits trigonal planar geometry and thus, a bond angle of approximately 120 degrees.

Identify molecules with sp^3 hybridization

Molecules with tetrahedral geometry exhibit sp^3 hybridization. In this case, only \(\mathrm{PF}_{3}\) exhibits tetrahedral geometry and thus, sp^3 hybridization.

Identify linear molecules

Molecules are considered to be linear when all atoms are in a straight line. In this case, \(\mathrm{SO}_{2}, \mathrm{NNO}\), and \(\mathrm{COS}\) are linear molecules.

Key concepts

Molecular Polarity

Molecular polarity is a critical concept in chemistry that helps us understand how molecules interact with each other and with other substances. A molecule is considered polar if it has a net dipole moment, meaning that its charge distribution is uneven. This results from the asymmetric arrangement of atoms and the distribution of electrons within the molecule.

Polarity arises because of differences in electronegativity between bonded atoms. When atoms with different electronegativities form a bond, the electrons are not shared equally, leading to partial charges on the atoms. When these partial charges are not balanced in the molecule, due to its shape or the orientations of the bonds, the molecule is polar.

For example, in the exercise, \(\mathrm{SO}_{2}\), \(\mathrm{COS}\), and \(\mathrm{NNO}\) are polar because they have an asymmetrical distribution of electron density. This unbalance causes a separation of charge within the molecule, allowing it to have distinct ends, one positive and one negative. Polar molecules usually have noticeable physical properties, such as higher boiling points and solubility in water, compared to nonpolar molecules.

Molecular Geometry

Molecular geometry refers to the three-dimensional arrangement of atoms within a molecule. It influences the physical and chemical properties of a substance, including reactivity, color, phase of matter, and polarity. The geometry is determined by the valence shell electron pair repulsion (VSEPR) theory, which states that electron pairs around a central atom will arrange themselves as far apart as possible to minimize repulsion.

Common molecular shapes include linear, trigonal planar, tetrahedral, trigonal bipyramidal, and octahedral. In the given exercise, we see an example of trigonal planar geometry in \(\mathrm{PCl}_{3}\), which exhibits bond angles of approximately 120 degrees due to three groups of electrons around the phosphorus atom. Understanding molecular geometry is crucial for predicting the behavior and reactivity of molecules in various conditions.

sp3 Hybridization

The concept of sp3 hybridization is vital for understanding how atoms form strong bonds in certain molecular geometries. It occurs when one s-orbital and three p-orbitals in an atom's valence shell mix to form four equivalent sp3 hybrid orbitals. These hybrid orbitals have a tetrahedral orientation, with angles of approximately 109.5 degrees between them.

sp3 hybridization is common in molecules where the central atom forms four single bonds. In our exercise, \(\mathrm{PF}_{3}\) is an example of a molecule with sp3 hybridization. The phosphorus atom has one lone pair and forms three single bonds with fluorine atoms, resulting in a tetrahedral shape due to this hybridization. Recognizing the type of hybridization can help predict the molecule's geometry and its reactivity patterns in chemical reactions.

Valence Electrons

Valence electrons are the electrons in the outermost shell of an atom and they play a pivotal role in chemical bonding and molecule formation. These electrons determine the atom's bonding behavior, as they can be shared with other atoms to form compounds or exist as lone pairs.

In the context of drawing Lewis structures, as in the given exercise, counting valence electrons is the first step. This count helps to determine how atoms can bond and the distribution of electrons around the central atom. For instance, sulfur in \(\mathrm{SO}_{2}\) has six valence electrons, while oxygen also has six, totaling eighteen for the molecule. Correctly identifying the number of valence electrons is essential for creating accurate Lewis structures, which in turn provides insights into molecular properties and behaviors.