The bond formed when two electrons that are shared between two atoms are donated by only one of the atoms is

Analyze the question: It asks for the type of bond in which the shared pair of electrons comes from only one atom.

Concept:

• Ionic bond: electrons are transferred from one atom to another, forming oppositely charged ions.
• Covalent bond: each atom contributes one electron to the shared pair.
• Dative (coordinate) bond: both shared electrons come from one atom, the donor. The other atom, the acceptor, must have an empty orbital.
• Metallic bond: positive metal ions are held together by a "sea" of delocalised electrons.

Solution:

1. The two electrons are shared, so the bond is not ionic and not metallic.
2. Both electrons come from only one atom, so it is not an ordinary covalent bond, where each atom gives one electron.
3. This is the definition of a dative (coordinate covalent) bond.

Examples:

• Ammonium ion, NH₄⁺: the lone pair on N in NH₃ is donated to H⁺ (which has an empty orbital).
• Hydroxonium ion, H₃O⁺: the lone pair on O in H₂O is donated to H⁺.

An ordinary covalent bond is technically also "shared electrons", but the specific detail that only one atom donates both electrons points to the dative bond.

Answer: B. dative

Exam tip: Remember "Dative = Donor". If one atom donates both electrons in the shared pair, it is dative. Look for lone-pair donors like NH₃ and H₂O, and an acceptor like H⁺.