Question

Draw Lewis structures, showing all valence electrons, for these molecules. (a) \(\mathrm{C}_{2} \mathrm{H}_{6}\) (b) \(\mathrm{CS}_{2}\) (c) \(\mathrm{HCN}\)

Short answer

Question: Draw the Lewis structures for Ethane (\(\mathrm{C}_{2}\mathrm{H}_{6}\)), Carbon disulfide (\(\mathrm{CS}_{2}\)), and Hydrogen cyanide (\(\mathrm{HCN}\)). Answer: The Lewis structures for the given molecules are as follows: Ethane (\(\mathrm{C}_{2}\mathrm{H}_{6}\)): H | H - C - C - H | H Carbon disulfide (\(\mathrm{CS}_{2}\)): S = C = S Hydrogen cyanide (\(\mathrm{HCN}\)): H - C ≡ N

Step-by-step solution

Find the total number of valence electrons

For each molecule, add up the valence electrons of each atom. The number of valence electrons are as follows: Carbon (C) - 4, Hydrogen (H) - 1, Sulfur (S) - 6, and Nitrogen (N) - 5. (a) \(\mathrm{C}_{2}\mathrm{H}_{6}\) Total valence electrons = (2 x 4) + (6 x 1) = 14 (b) \(\mathrm{CS}_{2}\) Total valence electrons = (1 x 4) + (2 x 6) = 16 (c) \(\mathrm{HCN}\) Total valence electrons = (1 x 1) + (1 x 4) + (1 x 5) = 10

Draw the first connections between atoms

Create single bonds between the central atom and the surrounding atoms. In these cases, carbon is the central atom. (a) \(\mathrm{C}_{2}\mathrm{H}_{6}\) - Two carbon atoms should be connected to each other, with hydrogen atoms surrounding them. (b) \(\mathrm{CS}_{2}\) - The carbon atom should be connected to two sulfur atoms. (c) \(\mathrm{HCN}\) - Hydrogen and nitrogen atoms should be connected to the carbon atom.

Distribute the remaining valence electrons

Distribute the remaining valence electrons around the molecules, making sure each atom (except hydrogen) has an octet. (a) \(\mathrm{C}_{2}\mathrm{H}_{6}\) H | H - C - C - H | H (b) \(\mathrm{CS}_{2}\) S = C = S (c) \(\mathrm{HCN}\) H - C ≡ N So, we have successfully drawn the Lewis structures for \(\mathrm{C}_{2}\mathrm{H}_{6}\), \(\mathrm{CS}_{2}\), and \(\mathrm{HCN}\).

Key concepts

Valence Electrons

Valence electrons are the outermost electrons found in an atom and play a crucial role in determining how atoms interact with each other to form chemical bonds.
They are involved in the formation of bonds between atoms in a molecule. - For example, carbon has 4 valence electrons, which gives it the ability to form up to four bonds with other atoms. - Hydrogen, with only 1 valence electron, typically forms only one bond. - Nitrogen and sulfur have 5 and 6 valence electrons respectively, allowing them a range of bonding possibilities. Knowing the number of valence electrons helps predict how atoms will bond.
This is crucial for drawing Lewis structures, as it allows we to layout the initial framework and connections between the atoms.

Chemical Bonding

Chemical bonding occurs when atoms share or exchange electrons to achieve a full outer shell of electrons, which leads to more stable molecules.
There are different types of chemical bonds, including covalent bonds, ionic bonds, and metallic bonds. - In the molecules we looked at, such as - - Carbon in - - - - - Generally, sharing pairs of electrons forms covalent bonds.
For instance, in the molecule Understanding chemical bonding is essential in explaining how molecules are held together.
It also provides insight into the physical and chemical properties of the substances we deal with in chemistry.

Octet Rule

The octet rule is a key concept in understanding why atoms bond the way they do.
It states that most atoms strive to have eight electrons in their valence shell, akin to the electron configuration of noble gases, which are inherently stable. - In Lewis structures, we often arrange electrons such that each atom (except hydrogen) attains an "octet." - For example, in At times, certain elements may not follow the octet rule, especially those in Period 3 and beyond, where expanded octets can occur.
However, for the basics, ensuring each atom (again, except hydrogen) reaches this 'magic number' of eight valence electrons paves the way for understanding molecular bonding in most compounds.
The octet rule simplifies our understanding of molecular stability and helps in predicting the formation and shape of molecules.