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Difficulty: MediumCovalent and Dative (Coordinate) Bonding

Complete the statement below regarding the chemical reaction between ammonia and boron trifluoride.

Answer:In the formation of the adduct between ammonia (NH3NH_3) and boron trifluoride (BF3BF_3), the nitrogen atom contributes both electrons to form the chemical bond with boron. This type of linkage is known as a 【dative covalent】 bond, and nitrogen functions as the electron pair 【donor】.

Answer

Blank 1 should be filled with 'dative covalent' (or 'coordinate covalent'), and Blank 2 should be filled with 'donor' (or 'Lewis base').
When NH3NH_3 reacts with BF3BF_3, nitrogen donates its unshared lone pair of electrons into the empty p-orbital of the electron-deficient boron atom. A covalent bond where one atom contributes both bonding electrons is a dative (coordinate covalent) bond, and the species donating the electron pair is the donor (or Lewis base).

Step-by-Step Solution

1
Examine the valence electron configurations of the reacting species.
Ammonia (NH3NH_3) has a non-bonding lone pair on the nitrogen atom, whereas boron trifluoride (BF3BF_3) has an incomplete octet with only six valence electrons around the central boron atom.
Determining the presence of unshared pairs and electron deficiency identifies the roles of each atom.
2
Identify the nature of the bond formed between nitrogen and boron.
Nitrogen shares its unshared lone pair to complete the octet of the boron atom, forming a bond where both shared electrons originate from nitrogen.
A covalent bond in which one atom provides both shared electrons is defined as a dative or coordinate covalent bond.
3
Assign the appropriate terminology to the electron-donating species.
The atom or molecule supplying the shared electron pair is termed the electron pair donor or Lewis base.
By definition in Lewis acid-base theory, the species donating the electron pair is the donor.

Key Concept

Dative (Coordinate) Covalent Bonding and Lewis Acid-Base Theory
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Topics

Covalent and Dative (Coordinate) Bonding

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