Molecular Properties

The molecular properties of shape, polarity and intermolecular bond type can be determined for a molecular compound (or element) by way of the Lewis structure. This page reviews how to create the Lewis structure for a molecular substance, then how to determine the shape and polarity of those molecules, and finally determine the type of intermolecular forces that would attract those molecules to one another.

Objective 14: From the name of a molecular substance, determine the Lewis structure for it

In these cases, you know that you are dealing with nonmetal atoms bonded together with covalent bonding and that (some of) the valence electrons of the atoms are shared between the atoms. What you need to figure out for each of these compounds is how those electrons are shared and depicted in terms of a Lewis structure.

Exercises

For each of the following molecule compounds, draw the Lewis structure for it.

a. iodine monobromide

b. sulfur dioxide

c. phosphorus trichloride

d. carbon monoxide

e. carbon disulfide

Answers

Objective 15: From the name of a molecular substance, determine the shape and polarity of the molecule

The general approach for simple molecules is to start with a Lewis diagram for the molecule. If there are more than two atoms, focus on the central atom in the molecule. Count the number of atoms bonded to the central atom and count the number of unbonded pairs of electrons on the central atom. Determine the molecular shape accordingly. Other shapes exist but we will not deal with them in this course.

To determine whether the molecule is polar, it is necessary to determine whether its charges are distributed symmetrically or not. The molecule is symmetric if it has a tetrahedral, trigonal planar, or linear shape, and all the outer atoms are the same element.

Exercises

For each of the following molecular compounds, determine the molecular geometry and polarity of the molecules.

a. boron trihydride

b. dichlorine monoxide

c. carbon dioxide

d. sulfur trioxide

e. nitrogen trifluoride

Answers

a. trigonal planar - nonpolar

b. bent - polar

c. linear - nonpolar

d. trigonal planar - nonpolar

e. trigonal pyramidal - polar

Objective 16: From the name of a molecular chemical determine the type of intermolecular forces it has

To do this you must first determine the shape and polarity of the molecule. If the molecule is nonpolar, it will have dispersion forces. If the molecule is polar and does not have hydrogen bonded to nitrogen, oxygen or fluorine, it will have dipole-dipole forces. If the molecule is polar and does have hydrogen bonded to nitrogen, oxygen or fluorine, it will have hydrogen bonding IMFs.

Exercises

For each of the following molecular compounds, determine the type of intermolecular forces it has.

a. water

b. carbon monoxide

c. carbon tetrachloride

d. sulfur dichloride

e. hydrogen fluoride

Answers

a. hydrogen bonding

b. dipole-dipole forces

c. dispersion forces

d. dipole-dipole forces

e. hydrogen bonding