Question

Do you expect the carbon hydrides of the type \(\left(\mathrm{C}_{\mathrm{n}} \mathrm{H}_{2 n+2}\right)\) to act as 'Lewis' acid or base? Justify your answer.

Short answer

Alkanes are neither Lewis acids nor bases due to their stable covalent bonds and lack of electron-donating or accepting ability.

Step-by-step solution

Understand Lewis Acid and Base Definitions

A Lewis acid is a substance that can accept a pair of electrons, while a Lewis base is a substance that can donate a pair of electrons. This concept is centered around the ability of an atom or molecule to either accept or donate electron pairs.

Identify Characteristics of Carbon Hydrides

Carbon hydrides with the formula \(\mathrm{C}_{\mathrm{n}}\mathrm{H}_{2 n+2}\) are alkanes. These compounds have saturated carbon-carbon and carbon-hydrogen single bonds. In the structure of alkanes, each carbon atom forms four single bonds (sp3 hybridization), which results in all electrons being shared in these interactions.

Analyze Electron Availability in Alkanes

Since alkanes such as \(\mathrm{C}_{\mathrm{n}}\mathrm{H}_{2 n+2}\) have fully satisfied covalent bonding, there are no lone pairs of electrons available to donate. Thus, they have no capability to act as a Lewis base.

Assess Potential to Accept Electrons

Alkanes do not have empty or low energy orbitals into which they can accept electrons, making them incapable of acting as Lewis acids either. Their chemical structure is very stable and does not readily engage in reactions that involve electron transfer.

Conclude Alkane Activity as Lewis Acid/Base

Given the lack of lone pairs for donation and the absence of an electron-accepting capability, alkanes \((\mathrm{C}_{\mathrm{n}}\mathrm{H}_{2n+2})\) are neither Lewis acids nor Lewis bases. They are quite inert due to their saturated hydrocarbon nature.

Key concepts

Alkanes

Alkanes are a fascinating group of organic compounds that follow the general formula \(\mathrm{C}_{\mathrm{n}}\mathrm{H}_{2\mathrm{n}+2}\). This means that these molecules consist solely of carbon and hydrogen atoms arranged in simple chain-like structures. One of the key characteristics of alkanes is that they are saturated hydrocarbons. This means every carbon atom is bonded to the maximum number of hydrogen atoms possible.

• They feature only single bonds between carbon atoms, making them relatively stable and less reactive compared to other hydrocarbons such as alkenes or alkynes.
• The carbon-carbon bonds in alkanes are single covalent bonds, typically assumed to have a bond angle of 109.5 degrees, which is consistent with \(sp^3\) hybridization.
• Due to their lack of unsaturation (double or triple bonds), alkanes do not readily engage in chemical reactions, explaining why they are often referred to as "paraffins."

This stability leads to their primary uses as fuels and lubricants, with products like methane, propane, and butane being prominent examples. Alkanes are a fundamental part of the chemical world due to their simple yet stable structure.

sp3 Hybridization

The concept of \(sp^3\) hybridization plays a significant role in understanding the geometry and bonding nature of alkanes. In \(sp^3\) hybridization, one s orbital and three p orbitals in an atom's valence shell mix to form four equivalent hybrid orbitals.

• These hybrid orbitals form a tetrahedral geometry around the carbon atom, each with equal energy and oriented at an angle of approximately 109.5 degrees to each other.
• This tetrahedral arrangement allows for the formation of single bonds with hydrogen atoms or neighboring carbon atoms, ensuring a stable, robust configuration.

In alkanes, such as those with the formula \(\mathrm{C}_{\mathrm{n}}\mathrm{H}_{2\mathrm{n}+2}\), every carbon atom undergoes \(sp^3\) hybridization. Understanding \(sp^3\) hybridization is key to recognizing why alkanes are nonpolar and exhibit limited chemical reactivity. Their fully saturated state means that all available electrons are involved in bonding, leaving no room for lone pairs or electron donation; thus, these molecules are rather inert.

Electron Pair Donation and Acceptance

The ability to donate or accept electron pairs distinguishes molecules as Lewis acids or bases. According to Lewis theory:

• Lewis Acids are electron pair acceptors. They can accept electron pairs from donors because they generally have empty orbitals or a positive charge.
• Lewis Bases are electron pair donors. They can donate a pair of electrons due to the presence of lone pairs or excess electrons.

Alkanes, represented by \(\mathrm{C}_{\mathrm{n}}\mathrm{H}_{2\mathrm{n}+2}\), do not fit into these categories because:

• They do not possess lone pairs of electrons due to their complete \(sp^3\) hybridization, which distributes all valence electrons in stable bonds.
• They also lack the empty orbitals needed to accept electrons, leaving them without the capability to act as electron pair acceptors.

Thus, because alkanes neither donate nor accept electron pairs, they do not function as Lewis acids or bases. Their inertness and lack of reactivity are due to this stable electron configuration, preventing engagement in typical acid-base reactions.