Nitrogen and ammonia
Introduced| English | Meaning |
|---|---|
| ammonia/æˈməʊnɪə/ | A compound of nitrogen and hydrogen with the formula NH3. |
| lone pair/ləʊn peə/ | A pair of outer-shell electrons on one atom that is not shared in a covalent bond. |
| ammonium ion/æˈməʊnɪəm ˈaɪɒn/ | The NH4+ ion, formed when ammonia accepts a proton. |
| triple bond/ˈtrɪpl bɒnd/ | A covalent bond involving three shared pairs of electrons. |
| non-polar/nɒn ˈpəʊlə/ | Having no significant separation of electric charge in a bond, or no overall permanent dipole in a molecule. |
| coordinate bond/kəʊˈɔːdɪnət bɒnd/ | A covalent bond in which both shared electrons were supplied by the same atom. |
From the air to fertiliser
- Nitrogen gas, $\text{N}_2$, fills the air but reacts with very little.
- Ammonia 氨 is a base, thanks to a lone pair 孤对电子 on its nitrogen.
- That lone pair also builds the ammonium ion 铵离子.
Ammonia (NH₃) acts as a base because it can accept a ______.
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NH₃ + H⁺ → NH₄⁺.
Why nitrogen is unreactive
- The two N atoms are joined by a triple bond 三键 with a very high bond energy — hard to break.
- The molecule is symmetrical and non-polar 非极性 — nothing pulls other molecules towards it.
Nitrogen is unreactive: a strong triple bond and no polarity
Ammonia is converted into nitrogen fertilisers
The shape of ammonia
Ammonia has three bonding pairs and one lone pair — the lone pair pushes the bonds down into a pyramidal shape (about 107°).
Nitrogen gas is unreactive because it has:
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The N≡N triple bond is very strong, and the symmetrical molecule is non-polar — both make it unreactive.
Match each nitrogen/ammonia fact.
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Each item links the term to its correct meaning.
Ammonia and the ammonium ion
- Ammonia is a base because the lone pair on nitrogen can accept a proton:
$$\text{NH}_3 + \text{H}^{+} \rightarrow \text{NH}_4^{+}$$
- The new N–H bond is a coordinate bond 配位键 (both electrons from N). The $\text{NH}_4^{+}$ ion has four identical N–H bonds and is tetrahedral.
Ammonia's lone pair accepts a proton, forming the ammonium ion by a coordinate bond
Ammonia acts as a base because:
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A Brønsted–Lowry base accepts a proton; ammonia's nitrogen lone pair does exactly that.
The bond formed when NH₃ accepts H⁺ is a coordinate bond because:
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Nitrogen supplies both electrons of the new N–H bond, making it a coordinate (dative) bond.
Testing for an ammonium salt
- Warm an ammonium salt with a base (NaOH) to push out ammonia:
$$\text{NH}_4\text{Cl} + \text{NaOH} \rightarrow \text{NaCl} + \text{NH}_3 + \text{H}_2\text{O}$$
- The sharp smell, and damp red litmus turning blue, confirms an ammonium salt.
The test for an ammonium salt is to warm it with NaOH and look for:
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A base displaces ammonia from the salt; the ammonia smells sharp and turns damp red litmus blue.
You've got it
- $\text{N}_2$ is unreactive: a strong triple bond + a non-polar molecule
- ammonia is a base — its lone pair accepts a proton → $\text{NH}_4^{+}$ (a coordinate bond, tetrahedral)
- test for an ammonium salt: warm with NaOH → ammonia (sharp smell, red litmus → blue)