The bond between NH$_3$ and H$^+$ in NH4$^+$ is?

Step 1: Analyze the question The question asks what type of bond forms when an NH₃ molecule joins to an H⁺ ion to make the ammonium ion, NH₄⁺.

Step 2: The concept

• In NH₃, nitrogen has 5 valence electrons. Three are shared with hydrogen atoms, leaving one lone pair.
• H⁺ has no electrons, only an empty 1s orbital.
• When one atom supplies both electrons of the shared pair, the bond is called a dative covalent (coordinate) bond.

Step 3: Working

1. NH₃ has a lone pair on nitrogen.
2. H⁺ has an empty orbital that can accept a pair of electrons.
3. Nitrogen donates its lone pair to H⁺, forming N→H.

H₃N: + H⁺ → [H₃N→H]⁺

4. Once formed, all four N–H bonds in NH₄⁺ are identical. But the question asks specifically about the bond between NH₃ and H⁺, which is the one formed by donation of the lone pair.

Step 4: Check the other options

• B. Covalent: This is partly true, since a dative bond is a type of covalent bond. However, "dative" is the more specific and correct answer, because both electrons come from nitrogen.
• C. Hydrogen: This is a weak intermolecular attraction (such as between H and N, O or F on different molecules). It is not the bond formed here.
• D. Electrovalent: This involves the transfer of electrons to form ions, which does not happen here.

Answer: A. dative

Exam tip: Whenever you see NH₄⁺, H₃O⁺, or similar ions formed by adding H⁺ to a molecule with a lone pair (NH₃, H₂O), think dative/coordinate bond. The key phrase is "one atom supplies both electrons."