Question

What are electron deficient compounds ? Are \(\mathrm{BCl}_{3}\) and \(\mathrm{SiCl}_{4}\) electron deficient species? Explain.

Short answer

\(\mathrm{BCl}_3\) is electron deficient, but \(\mathrm{SiCl}_4\) is not.

Step-by-step solution

Define Electron Deficient Compounds

Electron deficient compounds are chemical species where the central atom does not have a complete octet of electrons. This often occurs in compounds containing Group 13 elements, which are capable of forming bonds without adhering to the octet rule.

Evaluate \\(\mathrm{BCl}_3\\) as Electron Deficient

\(\mathrm{BCl}_3\) (Boron Trichloride) is an example of an electron deficient compound. Boron has 3 valence electrons and forms 3 covalent bonds with chlorine atoms. However, it only achieves a total of 6 electrons in its valence shell, indicating a deficiency of 2 electrons to complete the octet.

Evaluate \\(\mathrm{SiCl}_4\\) as Electron Deficient

\(\mathrm{SiCl}_4\) (Silicon Tetrachloride) involves silicon, which has 4 valence electrons. Silicon forms 4 covalent bonds with chlorine atoms, achieving a total of 8 electrons in its valence shell. This means silicon satisfies the octet rule and \(\mathrm{SiCl}_4\) is not an electron deficient compound.

Key concepts

Incomplete Octet

An incomplete octet is a condition where the central atom in a molecule does not have a complete set of 8 electrons in its valence shell.
This is essential for understanding the behavior of certain compounds that do not conform to the typical stability provided by a complete octet.

A classic example of an incomplete octet can be found in compounds involving certain Group 13 elements.

• In \(\mathrm{BCl}_3\), for example, boron forms three covalent bonds with chlorine but only has 6 electrons in its outer shell. This makes it electron deficient as it lacks the 8 electrons required to fulfill the octet rule.

This scenario leads the molecule to seek electrons from other sources or react with other compounds to achieve stability.
Understanding incomplete octets helps us predict the reactivity and bonding behavior of electron deficient compounds.

Group 13 Elements

Group 13 elements, also known as the boron group, are significant when discussing electron deficient compounds.
These elements include boron (B), aluminum (Al), gallium (Ga), indium (In), and thallium (Tl). The characteristic feature of these elements is their three valence electrons.

• Because of their fewer valence electrons compared to other groups, they often form compounds that do not fill the usual octet.
• They tend to participate in covalent bonding to balance their electron deficiency.

In particular, boron and aluminum are commonly found in compounds that deviate from the octet rule.
Knowing the properties of Group 13 elements aids in identifying and predicting how these elements will behave in chemical reactions, allowing for a better understanding of why these electron deficient states occur.

Covalent Bonding

Covalent bonding is when two atoms share pairs of electrons. It plays a crucial role in how elements achieve stable electronic configurations.
This type of bonding occurs frequently in compounds of Group 13 elements, where achieving a complete octet through electron sharing can be challenging.

In molecules like \(\mathrm{BCl}_3\), each chlorine atom shares one electron with boron. This forms three covalent bonds but leaves boron with only 6 electrons in its valence shell.

• Covalent bonding is essential in explaining why some molecules remain stable despite not following the octet rule.
• Understanding these interactions helps elucidate why electron deficient compounds can exist stably in certain conditions.

These scenarios highlight the diversity in chemical bonding and the exceptions that exist beyond simple rules.

Octet Rule

The octet rule is a principle stating that atoms tend to form bonds until they are surrounded by 8 electrons in their valence shell.
This is because a full set of 8 electrons typically provides chemical stability, reminiscent of the noble gases.

However, in the case of electron deficient compounds such as \(\mathrm{BCl}_3\), the central atom does not fulfill this rule.

• For boron, satisfying the octet is not possible through just its covalent bonds due to its three valence electrons.
• This deviation is often observed in compounds containing Group 13 elements, leading to exceptions in the octet rule.

Understanding the octet rule and its exceptions helps in recognizing why some compounds don't fit the perceived norm and still maintain their structural integrity.