Use electron dot structures to model the reaction between NH3 and BF3. Use an arrow to show how the electron pair is donated. Identify the Lewis acid, Lewis base, and the electron pair.
The Correct Answer and Explanation is:
To model the reaction between ammonia (NH₃) and boron trifluoride (BF₃) using electron dot structures, we first need to identify the electron dot structures for each molecule.
- Electron Dot Structure of NH₃:
- Ammonia has a nitrogen atom bonded to three hydrogen atoms. Nitrogen has five valence electrons, and each hydrogen atom contributes one electron. In total, nitrogen has one lone pair and three bonding pairs:
[
\text{H} \quad \text{H} \quad \text{H} \
\quad \quad \cdots \quad \
\text{N} \
\quad \cdots \quad \
]
Here, the lone pair on nitrogen can be represented as dots.
- Electron Dot Structure of BF₃:
- Boron trifluoride has a boron atom bonded to three fluorine atoms. Boron has three valence electrons, and fluorine contributes one electron each. Boron does not have a complete octet and has no lone pairs:
[
\text{F} \quad \text{F} \quad \text{F} \
\quad \quad \cdots \quad \
\text{B} \
]
Each fluorine atom has three lone pairs of electrons, while boron is electron-deficient.
Reaction Mechanism
When ammonia reacts with boron trifluoride, ammonia acts as a Lewis base, and boron trifluoride acts as a Lewis acid. The nitrogen atom in ammonia has a lone pair of electrons that it can donate to the electron-deficient boron atom in BF₃.
The reaction can be illustrated with an arrow indicating the donation of the lone pair:
[
\text{H}_2\text{N} \cdots \text{B} + \text{F}_3 \to \text{H}_2\text{N}-\text{B} \cdots \text{F}_3
]
The arrow points from the lone pair of nitrogen in NH₃ to the boron in BF₃, illustrating the donation of the electron pair.
Identification
- Lewis Acid: BF₃ (it accepts an electron pair).
- Lewis Base: NH₃ (it donates an electron pair).
- Electron Pair: The lone pair on the nitrogen atom of NH₃ that is donated to the boron atom of BF₃.
Explanation
This reaction demonstrates the classic Lewis acid-base interaction, where the Lewis acid (BF₃) has an incomplete octet and is electron-deficient, while the Lewis base (NH₃) has a lone pair of electrons. The donation of the electron pair allows BF₃ to achieve a stable electronic configuration, forming a coordinate covalent bond between nitrogen and boron. This bond formation is essential in many chemical processes, particularly in organic synthesis and coordination chemistry. Understanding these interactions enhances our grasp of reactivity and the nature of molecular interactions.