Question

Draw a Lewis structure for each of the following covalent compounds: a. \(\mathrm{OF}_{2}\) b. \(\mathrm{NI}_{3}\) c. \(\mathrm{CS}_{2}\) d. \(\mathrm{Cl}_{2} \mathrm{CO}\) (carbon is the central atom)

Short answer

For OF2, a bent molecule with O in the center, single bonds to F, and 6 additional electrons on O. NI3 consists of a central N with single bonds to three I atoms, each I with 6 additional electrons. In CS2, C is in the center with double bonds to each S atom. For Cl2CO, double bond C=O in the center, single bonds to two Cl atoms, with each Cl having 6 additional electrons.

Step-by-step solution

Drawing Lewis Structure for OF2

First, count the total valence electrons for the molecule, which is 6 for oxygen plus 2x7 for the two fluorine atoms, giving 20 electrons. Write the elemental symbols with oxygen in the middle and fluorine atoms on either side. Connect each fluorine to the oxygen with a single bond, using 4 electrons. Complete the octets of the fluorine atoms with the remaining electrons, and ensure that oxygen has 8 electrons around it, which might involve sharing more pairs with fluorine to form double bonds if needed.

Drawing Lewis Structure for NI3

Total valence electrons are 5 for nitrogen plus 3x7 for the three iodine atoms, giving 26 electrons. Place nitrogen in the middle and arrange the iodine atoms around it. Connect each iodine to nitrogen with a single bond, thus using 6 electrons. Distribute the remaining electrons to complete the octets of the iodine atoms. Check that nitrogen has an octet; it might share additional pairs of electrons with iodine atoms if needed.

Drawing Lewis Structure for CS2

Count the total valence electrons: 4 from carbon and 2x6 from the two sulfur atoms, giving 16 electrons. Place carbon in the center and sulfur atoms on the sides. Form double bonds between carbon and each sulfur atom to make sure every atom has an octet, using 16 electrons in total. Ensure that no electrons are left over or missing.

Drawing Lewis Structure for Cl2CO

Count the total valence electrons: 4 from carbon, 2x7 from the two chlorine atoms, and 6 from oxygen, giving 24 electrons. Write carbon in the middle, flanked by chlorine atoms and oxygen at one end. Form a double bond between carbon and oxygen, and a single bond between carbon and each chlorine. Use remaining electrons to complete the octets of chlorine and oxygen atoms.

Key concepts

Valence Electrons

Valence electrons are the electrons in the outermost shell of an atom that participate in chemical reactions by forming bonds with other atoms. These electrons are crucial because they are the ones that atoms use to gain stability by either sharing with or transferring to other atoms. In the context of drawing a Lewis structure, understanding the number of valence electrons a given atom has can be the first step towards predicting how atoms will bond together.

For instance, in the provided exercise, to draw the Lewis structure of \textbf{OF}\(_2\), we start by determining that oxygen has 6 valence electrons and each fluorine has 7. The total is 20 valence electrons that must be accounted for in the Lewis structure. Similarly, for other compounds like \textbf{NI}\(_3\), \textbf{CS}\(_2\), and \textbf{Cl}\(_2\)\textbf{CO}, knowing the valence electrons guides the way these structures are drawn. It's significant to remember that the electrons involved in bonding are primarily the valence electrons.

Octet Rule

The octet rule is a principle in chemistry that states atoms tend to bond in such a way that they each end up with eight electrons in their valence shell, giving them the same electronic configuration as a noble gas. This rule is a helpful guideline for understanding the driving force behind most chemical bonds. However, it's important to note that there are exceptions to the octet rule where compounds may be stable with less or more than eight electrons around an atom.

When applying the octet rule in drawing Lewis structures, atoms typically share or transfer electrons to achieve that stable octet formation. For example, in the \textbf{CS}\(_2\) molecule, each sulfur atom forms a double bond with carbon, which fulfills the octet rule for all atoms involved by using a total of 16 valence electrons. In the case of molecules that involve elements from the third period and beyond, like with \textbf{NI}\(_3\), the central atom might have more than eight electrons, due to the availability of d orbitals, but the octet rule is still a fundamental concept in understanding molecule formation.

Covalent Compounds

Covalent compounds are substances formed when two or more nonmetals share electrons in a covalent bond. The sharing of electrons allows each atom in the covalent compound to reach a stable electron configuration, often by adhering to the octet rule. The Lewis structures for these compounds illustrate the sharing of electron pairs between atoms.

In the exercise solutions, we see examples of covalent bonding where shared pairs of valence electrons are represented by lines between the atoms. For instance, in \textbf{Cl}\(_2\)\textbf{CO}, the covalent bonds between carbon and oxygen as well as carbon and chlorine are shown by lines, indicating the shared electrons. Covalent compounds often have unique properties such as lower melting and boiling points compared to ionic compounds, and they do not conduct electricity in solution. The Lewis structure representation provides insight into the molecule's structure, which is crucial for understanding the behavior and interaction of the compound.