Question

Which are Lewis acids and which are Lewis bases? (a) \(\mathrm{Cu}^{2+}\) (b) Cl" (c) \(\mathrm{SnCl}_{2}\) (d) \(\mathrm{OF}_{2}\)

Short answer

(a) Lewis acid (b) Lewis base (c) Lewis acid (d) Neither

Step-by-step solution

Identify Lewis Acids

Lewis Acids are species that accept an electron pair. Generally, these are cations or molecules with an incomplete octet.

Identify \( Cu^{2+} \) as a Lewis Acid

The ion \( Cu^{2+} \) has a positive charge and can accept an electron pair to become neutral. Therefore, \( Cu^{2+} \) is a Lewis acid.

Identify Lewis Bases

Lewis Bases are species that donate an electron pair. Generally, these are anions or molecules with a lone pair of electrons.

Identify \( Cl^{-} \) as a Lewis Base

The ion \( Cl^{-} \) has a negative charge and contains lone pairs of electrons that it donates. Therefore, \( Cl^{-} \) is a Lewis base.

Classify \( SnCl_{2} \)

The molecule \( SnCl_{2} \) has a central tin atom with an empty p-orbital that can accept electrons. Thus, \( SnCl_{2} \) is a Lewis acid.

Classify \( OF_{2} \)

The molecule \( OF_{2} \) has fluorine atoms with lone pairs of electrons. However, \( OF_{2} \) tends not to accept or donate any electron pairs under typical conditions. Therefore, \( OF_{2} \) does not fit perfectly as a Lewis acid or base.

Key concepts

Lewis Acid

A Lewis acid is a chemical species that can accept an electron pair. They are often cations or molecules with incomplete octets.
For example, in the exercise, \(Cu^{2+}\) is identified as a Lewis acid because it is a positively charged ion. This positive charge makes it eager to accept electrons to become neutral. Another example provided is \(\text{SnCl}_2\)\. This molecule has an empty p-orbital in its central tin atom, making it capable of accepting electron pairs.
In general:

• Cations are typically Lewis acids. Their positive charge means they lack electrons and thus can accept electron pairs to neutralize their charge.
• Molecules with an atom that has an incomplete octet are also Lewis acids. As they do not have a complete valence shell, they accept electron pairs to achieve stability.

Lewis Base

A Lewis base is a chemical species that can donate an electron pair. They are often anions or neutral molecules with lone pairs of electrons. For instance, in the exercise, the \(Cl^{-}\) ion is identified as a Lewis base. It has a negative charge and contains lone pairs that it can donate in chemical reactions.
Common characteristics:

• Anions are typically Lewis bases. Their extra electrons make them willing to donate one or more pairs.
• Neutral molecules with lone pairs of electrons also act as Lewis bases. These lone pairs can be donated to other atoms or ions in need of electrons.

Electron Pair Donation

Electron pair donation is a key concept in understanding how Lewis bases function. When a Lewis base donates an electron pair, it interacts with a Lewis acid, which accepts this electron pair. This interaction often leads to the formation of a coordinate covalent bond.
For example, when \(Cl^{-}\) interacts with \(Cu^{2+}\), the chloride ion donates an electron pair to the copper ion, resulting in a stable interaction.
Key Points:

• The process is essential in many chemical reactions, such as the formation of coordination complexes.
• It helps in understanding reaction mechanisms, particularly in organic and inorganic chemistry.

Cation and Anion

Cations and anions play crucial roles in identifying Lewis acids and bases.
Cations:

• These are positively charged ions. Due to their lack of electrons, they act as Lewis acids.
• For example, \(Cu^{2+}\) is a cation that is willing to accept electron pairs.

Anions:

• These are negatively charged ions, which have extra electrons compared to their neutral state.
• They act as Lewis bases because they have electron pairs to donate. \(Cl^{-}\) is an example of an anion that donates electron pairs when it reacts with cations or other species needing electrons.

Understanding these concepts helps in predicting the reactivity and interaction of different chemical species.