Problem 49 - Chemistry Matter and Change

Question

Challenge Draw the Lewis structure for the molecule formed when six fluorine atoms and one sulfur atom bond covalently.

Step-by-Step Solution

Answer

The Lewis structure for the molecule formed when six fluorine atoms and one sulfur atom bond covalently (SF6) can be represented as: F | F - S - F | F In this molecule, Sulfur (S) is the central atom sharing single bonds with six Fluorine (F) atoms. There are 48 valence electrons in total; 12 are used for forming single bonds, and 36 are distributed as lone pairs on the fluorine atoms, completing their octets.

Step 1: Identify the central atom

In this molecule, sulfur (S) is the central atom as it can form more covalent bonds than fluorine (F). Sulfur can make up to six covalent bonds, whereas fluorine can only form one.

Step 2: Count the total valence electrons

We need to count the total valence electrons in the system to distribute them properly. Sulfur has six valence electrons, and each fluorine atom has seven. Since there are six fluorine atoms, we have a total of: \( 6(S) + 6 \times 7(F) = 6 + 42 = 48\) valence electrons.

Step 3: Place the central atom and arrange the surrounding atoms

Place the sulfur atom in the center of the molecule and surround it with six fluorine atoms.

Step 4: Create single bonds first

Distribute the electrons by creating single bonds (a pair of shared electrons) between the sulfur atom and each of the six fluorine atoms. Each single bond consumes two electrons, and as there are six single bonds in total, 12 electrons (6 x 2) will be used. There will be 36 electrons remaining (48 - 12).

Step 5: Complete the octets of surrounding atoms

Now, we'll complete the octets of the surrounding fluorine atoms by assigning the remaining 36 electrons. Each fluorine atom needs six more electrons to complete its octet. Six fluorine atoms will need a total of 36 electrons (6 x 6). Distribute these 36 electrons as lone pairs among the fluorine atoms, leaving no electrons remaining.

Step 6: Verify the octets

Check to make sure each fluorine atom now has an octet (eight electrons) and the central sulfur atom also has an octet by counting its shared and unshared electrons. The final Lewis structure for the molecule formed when six fluorine atoms and one sulfur atom bond covalently (SF6) is: F | F - S - F | F

Key Concepts

Covalent Bonds

Understanding the concept of covalent bonds is essential when drawing Lewis structures. Covalent bonds are formed when two atoms share one or more pairs of valence electrons to achieve greater stability. In a covalent bond, the shared electrons contribute to each atom's valence shell, enabling them to adhere to the octet rule or achieve a noble gas configuration.

For instance, in the molecule formed by sulfur and fluorine (SF₆), each fluorine atom shares one electron with sulfur, resulting in the formation of single covalent bonds. These bonds are depicted in the Lewis structure as straight lines connecting the central sulfur atom to each of the fluorine atoms. The sharing of electrons in covalent bonds is crucial for the molecule's stability and is a key element to represent correctly when constructing Lewis structures.

Valence Electrons

Identifying valence electrons plays a pivotal role in determining how atoms bond in a molecule. Valence electrons are the outermost electrons of an atom and are involved in the formation of chemical bonds. During the Lewis structure drawing process, you begin by counting these valence electrons since they will dictate how atoms can be joined.

In our exercise, sulfur has six valence electrons, while each fluorine has seven. To accurately represent the molecule SF₆, we must calculate the total number of valence electrons available for bond formation: six from sulfur plus forty-two from the six fluorine atoms, totaling forty-eight. These valence electrons are then distributed to form covalent bonds and complete the atoms' octets, as shown in the corresponding Lewis structure for SF₆.

Octet Rule

The octet rule is a fundamental principle in chemistry that helps explain the formation of covalent bonds in the Lewis structure. It states that atoms tend to form bonds in such a way that each atom has eight electrons in its valence shell, resembling the electron configuration of a noble gas. This rule applies to most elements, particularly those found in the second period of the periodic table and beyond.

In our example of the SF₆ molecule, each fluorine atom aims to complete its octet by having eight electrons in its valence shell. Since fluorine already has seven valence electrons, it requires one additional electron, which it obtains through forming a single covalent bond with sulfur. The central sulfur atom achieves an expanded octet by sharing electrons with all six fluorine atoms due to its ability to accommodate more than eight electrons. Although sulfur can exceed the octet, the aim is always to fill or satisfy the valence shells of the surrounding atoms according to the octet rule, which is visually confirmed in the final Lewis structure.