Question

Your roommate, a chemistry major, claims to have synthesized the compound \(\mathrm{CH}_{5}\) in the lab. Why is that not possible?

Short answer

The synthesis of the compound \(\mathrm{CH}_{5}\) is not possible because Carbon has a valency of 4, meaning it can only form 4 single bonds with other elements, while Hydrogen has a valency of 1. According to the octet rule, Carbon can form 4 single bonds with 4 Hydrogen atoms to reach a stable electron configuration with 8 electrons in its outer shell, such as in methane (\(\mathrm{CH}_{4}\)). However, bonding with 5 Hydrogen atoms would violate the valency and octet rule, making the compound \(\mathrm{CH}_{5}\) impossible to exist.

Step-by-step solution

Understand the elements in the compound

To understand the possibility of existence of the compound \(\mathrm{CH}_{5}\), we should focus on the elements present in that compound, Carbon (C) and Hydrogen (H), and their typical bonding behavior.

Review valency and bonding capacity of elements

Now, let's review the valency of Carbon and Hydrogen. Valency is the combining power of an element, which determines how many bonds it can make with other atoms. The valency of Carbon is 4, as it has 4 electrons in its outer shell, and the valency of Hydrogen is 1, as it has only one electron in its outer shell.

Observe the Octet Rule

We should also consider the octet rule, which states that atoms tend to combine in such a way that they have 8 electrons in their outer shell, giving them the same electronic configuration as a noble gas.

Determine the bonding possibilities of the compound

Based on the valency of Carbon and Hydrogen, Carbon can form 4 single bonds with other elements. In a typical organic compound, such as methane (\(\mathrm{CH}_{4}\)), Carbon forms 4 single bonds with 4 Hydrogen atoms. Each Hydrogen atom satisfies its valency with one bond, and Carbon reaches a stable electron configuration with 8 electrons in its outer shell.

Evaluate the possibility of the compound's existence

In the case of the compound \(\mathrm{CH}_{5}\), there would be 5 Hydrogen atoms surrounding a single Carbon atom. However, Carbon can only make 4 single bonds, which means bonding with 5 Hydrogen atoms is not possible, as it would violate the valency and octet rule. Therefore, the synthesis of the compound \(\mathrm{CH}_{5}\) is not possible, and your roommate's claim is incorrect.

Key concepts

Valency of Elements

Valency is a fundamental concept in chemistry that indicates the ability of an element to bond with other atoms. It defines the number of chemical bonds an atom can form based on the electrons present in its outermost shell, also known as the valence shell. For example, Hydrogen, with one electron in its outer shell, has a valency of 1, as it needs one more electron to achieve a full shell, or a duet configuration in its case.

Carbon, on the other hand, has four valence electrons. This gives Carbon a valency of 4, implying that it can form up to four bonds with other atoms to attain a full octet – a stable electronic configuration with eight electrons in its valence shell. Understanding the concept of valency is crucial as it guides us on how atoms combine to form molecules and informs us about the possible structures these molecules can take.

Octet Rule

The octet rule is a chemical principle that provides insight into the formation of chemical bonds in molecules. It states that atoms tend to combine in such a way that they each have eight electrons in their valence shell, mirroring the electron configuration of noble gases, which are inherently stable due to their complete outer shells.

However, there are exceptions to the octet rule, especially among molecules involving transition metals or those with an odd number of electrons, but for main group elements, reaching an octet is often a driving force behind bond formation. The octet rule helps predict how many bonds an atom is likely to form. It also helps explain the stoichiometry of compounds, as atoms will share, donate, or receive electrons to fulfill the rule.

Molecular Structure

Molecular structure determines the arrangement of atoms within a molecule and dictates its shape, size, and overall stability. It's influenced by the valency of the individual atoms and the need to achieve an octet configuration wherever applicable. Molecules range from simple diatomic species like hydrogen (H2) to complex organic structures.

The molecular structure is typically determined through a combination of valency and the octet rule, alongside principles such as the VSEPR (Valence Shell Electron Pair Repulsion) theory and hybridization. These principles help to predict the three-dimensional arrangement of atoms in a molecule and understand the angles between bonds, the presence of lone pairs, and any resultant polar or nonpolar characteristics.