Question

In ammonia-boron trifluoride complex, the donor molecule is

Short answer

Answer: The donor molecule in the ammonia-boron trifluoride complex is ammonia (NH3).

Step-by-step solution

Identifying the Coordination Complex

First, we need to write down the chemical formula for the ammonia-boron trifluoride complex. Ammonia is NH3, and boron trifluoride is BF3. The complex can be represented as NH3-BF3.

Understand Donor and Acceptor Molecules

In coordination complexes, a donor molecule is the one that donates a pair of electrons to form a coordinate covalent bond, while the acceptor molecule is the one that accepts the electron pair. Generally, the donor molecule has a lone pair of electrons available for bonding, while the acceptor molecule has an empty orbital to receive the electron pair.

Identify the Donor Molecule in the Complex

In the ammonia-boron trifluoride complex (NH3-BF3), ammonia (NH3) has a lone pair of electrons on the nitrogen atom, while boron trifluoride (BF3) has an empty orbital in the boron atom. The nitrogen atom in ammonia donates its lone pair of electrons to the empty orbital of boron in boron trifluoride, forming a coordinate covalent bond. Thus, the donor molecule in this complex is ammonia (NH3).

Key concepts

Donor Molecule

Understanding the role of a donor molecule in coordination complexes is foundational for grasping the intricacies of chemical bonding, especially in the formation of these complexes. A donor molecule, essential for the creation of a coordination complex, possesses a crucial characteristic: a set of electrons that are not involved in bonding, commonly known as a lone pair. This lone pair is pivotal as it is offered up for bonding.

In our case, the ammonia molecule (NH3) exemplifies the donor. Its nitrogen atom, due to its five valence electrons, has one pair that does not participate in the typical covalent bonding with hydrogen atoms. This unshared pair is what makes ammonia an excellent donor, capable of forming additional bonds by donating this pair to other molecules or ions that are seeking electrons -- these are termed acceptors.

Coordinate Covalent Bond

Diving deeper into coordination chemistry, we encounter a unique type of bonding known as the coordinate covalent bond. Unlike a traditional covalent bond, where two atoms share a pair of electrons with each contributing one electron, a coordinate covalent bond entails one atom providing both electrons for the shared pair. This is a fundamental concept in understanding coordination complexes.

To illustrate, the ammonia-boron trifluoride complex houses such a bond between the nitrogen atom of ammonia and the boron atom of boron trifluoride (BF3). Nitrogen, being electron-rich due to its lone pair, steps into the role of a donor and boron, with an electron deficiency, serves as an acceptor. The nitrogen atom donates its lone pair to the empty orbital of boron, establishing a bond that is characterized by the sharing of a pair of electrons stemming from one single atom – a characteristic feature of coordinate covalent bonds.

Lone Pair of Electrons

When discussing donor molecules and coordinate covalent bonds, the concept of a lone pair of electrons frequently emerges. But what exactly are lone pairs? Simply put, they are pairs of valence electrons that are not engaged in bonding with other atoms. These electrons reside on the outermost shell of an atom and possess the potential to form bonds with other atoms or ions, specifically through the donation of this pair to form a coordinate covalent bond.

In the structure of ammonia, for example, the nitrogen atom has five valence electrons which pair up to form one lone pair, while the remainder form covalent bonds with hydrogen atoms. The existence of this lone pair is significant as it grants the molecule its donor properties, enabling ammonia to engage with boron trifluoride and form a complex through a coordinate bond. Grasping the nature of lone pairs is integral to understanding the behavior of molecules in various chemical reactions and interactions.