Question

In the vapor phase, beryllium chloride consists of discrete \(\mathrm{BeCl}_{2}\) molecules. Is the octet rule satisfied for Be in this compound? If not, can you form an octet around Be by drawing another resonance structure? How plausible is this structure?

Short answer

The octet rule is not satisfied for Be in \( \mathrm{BeCl}_2 \). A resonance structure with an octet is implausible for Be.

Step-by-step solution

Understand the Octet Rule

The octet rule states that atoms tend to bond in such a way that each atom has eight electrons in its valence shell, achieving a noble gas electron configuration.

Analyze the Bonds in BeCl2

Beryllium chloride in the vapor phase has a linear structure as a molecule, with a beryllium atom covalently bonded to two chlorine atoms: \( \text{Cl} - \text{Be} - \text{Cl} \). Beryllium shares two electrons with each chlorine atom, leading to a total of four electrons around the beryllium.

Evaluate If the Octet Rule Is Satisfied

The octet rule is not satisfied for beryllium in \( \mathrm{BeCl}_2 \) because it only has four electrons in its valence shell instead of the required eight for a full octet.

Consider Resonance Structures

Draw a resonance structure by attempting to move lone pairs from chlorine to form a double bond with beryllium. This would mean \( \text{Cl} = \text{Be} = \text{Cl} \), which would provide more electrons around Be.

Evaluate the Plausibility of the Resonance Structure

In this resonance structure, beryllium would achieve an octet. However, this scenario is not plausible because beryllium is highly electropositive and unlikely to form double bonds due to its small size and low electron affinity. Resonance structures involving multiple bonds with Be are generally not supported by experimental evidence.

Key concepts

Beryllium Chloride

Beryllium chloride (\( \text{BeCl}_2 \)) is a compound that consists of one beryllium atom (\( \text{Be} \)) and two chlorine atoms (\( \text{Cl} \)). In the vapor phase, beryllium chloride exists in a linear molecular structure, represented as \( \text{Cl} - \text{Be} - \text{Cl} \). This indicates that beryllium is bonded to two chlorine atoms, forming a covalent bond with each.
Beryllium itself is a small, lightweight metal found in group 2 of the periodic table, known as the alkaline earth metals.
It holds interesting bonding characteristics, which influence its failure to fulfill the octet rule in certain compounds like \( \text{BeCl}_2 \). In the case of beryllium chloride, each chlorine atom shares one pair of electrons with the beryllium atom, which contributes to the linear structure suggested in its molecular form.

Covalent Bonding

Covalent bonding occurs when atoms share electron pairs, enabling them to achieve full valence shells. This kind of bonding is essential in the formation of molecules such as beryllium chloride.
In \( \text{BeCl}_2 \), beryllium shares a pair of electrons with each chlorine atom. This sharing is essential to maintaining molecular stability and forming covalent bonds.

• Each chlorine atom in \( \text{BeCl}_2 \) seeks to achieve a complete octet by sharing electrons with beryllium.
• Beryllium, however, only ends up with four electrons in its valence shell due to its bonding with the two chlorine atoms.

This sharing mechanism allows the formation of covalent compounds, even though it sometimes results in entities like \( \text{BeCl}_2 \) where the central element does not satisfy the octet rule.

Electron Configuration

Electron configuration describes the distribution of electrons in an atom or molecule's orbital structure. This concept helps understand why certain elements react in specific ways.
Beryllium's electron configuration is \( 1s^2 2s^2 \), with two electrons located in its \( 2s \) orbital.
When involved in bonding, these electrons are shared with other atoms, such as chlorine in \( \text{BeCl}_2 \).
The octet rule suggests that atoms are most stable when they have eight electrons in their outermost shell. While chlorine can complete its octet by sharing electrons with beryllium, beryllium itself, given its basic electron configuration, can only surround itself with four electrons when bonded in \( \text{BeCl}_2 \). This electron configuration limitation explains why beryllium does not satisfy the octet rule in this covalent structure.Current understanding and experimental evidence show that resonance structures where beryllium forms double bonds to accommodate an octet are not feasible due to these electronic interactions.