Nitrogen almost always forms three covalent bonds, which is why “three” is the answer in most textbooks and homework problems. It can form a fourth bond by putting its spare electrons to work, but only at the cost of carrying a positive charge. What it essentially never does is form five ordinary bonds, even though its neighbor phosphorus does this easily.1PubMed Central. The First Row Anomaly and Recoupled Pair Bonding in the Halides of the Late p-Block Elements
Why Nitrogen Usually Forms Three Bonds
Nitrogen has five valence electrons, the outer electrons that take part in bonding.2Chemistry LibreTexts. How Many Bonds Can Nitrogen Form Two of them sit together as a lone pair, two unshared electrons, and the other three are unpaired.3Chemistry LibreTexts. How Many Bonds Can Nitrogen Form Each unpaired electron can pair up with one from another atom, which gives three covalent bonds.4Chemistry LibreTexts. How Many Bonds Can Nitrogen Form The result is a full set of eight outer electrons, the octet, as in ammonia, NH3.5Chemistry LibreTexts. How Many Bonds Can Nitrogen Form
To draw ammonia, put an N down with five dots around it. Pair each of the three single dots with an electron from a hydrogen, and show the leftover pair of dots on top. Count the three shared pairs (six electrons) plus the two lone-pair electrons, and you reach eight.
The reason the pair stays a pair comes from how the electrons fill their orbitals. Two go into the 2s orbital together. The three 2p electrons then spread out one per orbital before any of them pair up. So the five outer electrons are not equivalent: one pair is set aside and three are free to bond. The lone pair isn’t used in bonding in ammonia, but it is the pair that makes a fourth bond possible.
You can check any finished nitrogen structure the same way. Count the bond lines touching the nitrogen and add the lone-pair dots. A neutral nitrogen should show three lines and one lone pair. If the count comes out different, either the nitrogen carries a charge or the drawing has an error, so the check tells you where to look. A double bond counts as two lines and a triple bond as three, so HCN, with one triple bond to carbon, still passes.
Three Bonds To One Partner The Triple Bond In Nitrogen Gas
Most of Earth’s air is nitrogen gas, N2, two nitrogen atoms joined to each other. Because each atom puts all three of its bonds into its partner, they form one triple bond.6EES Catalysis. Advancements in dinitrogen activation for catalytic breakthroughs That triple bond is among the most stable bonds in nature, taking nearly 10 eV to break.7EES Catalysis. Advancements in dinitrogen activation for catalytic breakthroughs
A triple bond is three shared pairs of electrons between the same two atoms, six electrons in all. Each nitrogen contributes its three unpaired electrons, so both atoms count all six. Add each atom’s lone pair and each nitrogen has eight, so N2 follows the same octet rule as ammonia.
More shared pairs between two nuclei pull them closer, so a triple bond is shorter than a double or single bond between the same atoms. The same pairing makes it harder to pull apart, which is why N≡N is so much stronger than a single N–N bond.
That strength means nitrogen gas barely reacts. It stays inert in your lungs, and it is why plants can’t use air nitrogen directly and industry needs heavy energy to make fertilizer. Lightning and certain bacteria are among the few natural ways to split it.
When Nitrogen Forms Four Bonds
Ammonia’s lone pair can grab a hydrogen ion, H+, which has no electrons of its own.8Wikipedia. Ammonium Nitrogen supplies both electrons for that bond, which is called a coordinate bond.9Wikipedia. Ammonium Once formed, all four N–H bonds in ammonium, NH4+, are identical.10Wikipedia. Ammonium Because nitrogen now shares its lone pair instead of owning it, the ion carries a +1 charge. This is also why ammonia acts as a base: its lone pair picks up H+ from water or an acid.
The charge follows from counting. In a drawing, nitrogen “owns” one electron from each of its four bonds, so four in all. That is one fewer than its normal five. Missing one electron gives a formal charge of +1, the charge you assign on a drawn structure. So four-bonded nitrogen is almost always in a positive ion.
To draw ammonium, start with the ammonia drawing: nitrogen, three N–H lines and a lone pair on top. Bring in H+ as a bare hydrogen with no electrons. Erase the lone-pair dots, since they now become the bond, draw a fourth line from nitrogen to the new hydrogen in their place, and put brackets around the structure with a + outside. Nitrogen now has four lines and eight electrons in total, a full set.
Nitrogen can likewise bond to four carbon groups, forming quaternary ammonium ions such as tetramethylammonium.11Brainly. When the nitrogen atom in an organic compound has four covalent bonds, it is called a quaternary ammonium ion Some of these four-group nitrogen compounds, called quats, are common disinfectants.12National Pesticide Information Center. Quaternary Ammonium Compounds Fact Sheet You meet them as ingredients like benzalkonium chloride on disinfectant wipe labels.
Charge can go the other way, too. Nitrogen can have two bonds and two lone pairs, a form that carries a −1 charge, as in the amide ion. Bonds plus lone pairs still add up to a full set of eight.
Can Nitrogen Form Five Bonds
Nitrogen sits in the first row of the p-block, where atoms are small and hold only eight outer electrons comfortably.13PubMed Central. The First Row Anomaly and Recoupled Pair Bonding in the Halides of the Late p-Block Elements Phosphorus, just below nitrogen, readily forms PF5 with five bonds.
An expanded octet means a central atom holds more than eight outer electrons, such as ten in PF5. Heavier atoms like phosphorus and sulfur can do this because they are larger and have more room around them. Phosphorus has the same five outer electrons as nitrogen, so the difference is size and available room, not electron count. Five neighbors crowd too close around a small nitrogen, and the fluorines in NF5 would sit closer than they comfortably can.14Journal of the American Chemical Society. NF5Viable or Not?
Calculations suggest NF5 could exist briefly, but not with five normal bonds.15Journal of the American Chemical Society. NF5Viable or Not? It would have three ordinary bonds plus one three-atom bond sharing just two electrons.16Journal of the American Chemical Society. NF5Viable or Not? It would fall apart into NF4 and a fluorine atom, releasing energy.17Wikipedia. Nitrogen pentafluoride – Wikipedia So for real compounds, four bonds is the most nitrogen forms.
Two things can make nitrogen look as if it has five bonds. Nitrate’s nitrogen has an oxidation state of +5, its maximum, yet it forms only four bond lines: one double and two single. Oxidation state is electron bookkeeping, not a bond count. Older books also call ammonium nitrogen “pentavalent.”18Wikipedia. Valence (chemistry) – Wikipedia That convention counted all five electrons used, not bonds formed. Today you count bonds, and ammonium has four.
Unusual Cases Chains Rings And Crushed Nitrogen
Squeezed above 110 GPa and heated over 2,000 K, nitrogen forms a solid where every atom has three single bonds, like diamond.19PubMed. Single-bonded cubic form of nitrogen In ordinary nitrogen gas, atoms bond in pairs with triple bonds. In the crushed solid, each atom bonds singly to three different neighbors, forming a connected network. Each atom still has three bonds, so the rule holds even though the arrangement is very different. At normal pressure triple-bonded N2 is far more stable.
A five-nitrogen ring ion, N5−, has been made in a stable salt.20PubMed. Synthesis and characterization of the pentazolate anion cyclo-N5- in (N5)6(H3O)3(NH4)4Cl It is a flat ring of five nitrogen atoms carrying one negative charge, with its electrons shared around the ring, which helps it hold together.
Nitrogen strongly prefers to snap back into N2, and nitrogen chains and rings release lots of energy when they do.21PubMed. Properties and Promise of Catenated Nitrogen Systems As High-Energy-Density Materials These compounds interest explosives and fuel researchers.22PubMed. Properties and Promise of Catenated Nitrogen Systems As High-Energy-Density Materials
In some iron clusters a single nitrogen atom sits inside, linked to four iron atoms.23PubMed. Controlled Expansion of a Strong-Field Iron Nitride Cluster: Multi-Site Ligand Substitution as a Strategy for Activating Interstitial Nitride Nucleophilicity Bonds to metal clusters are shared across several atoms, so counting them isn’t like counting textbook bonds. They don’t overturn the four-bond limit for normal molecules.
Hydrogen Bonds Are Not Extra Bonds
Nitrogen’s lone pair can attract a hydrogen on a neighboring molecule, which is called a hydrogen bond. These nitrogen hydrogen bonds help hold DNA’s two strands together.24PubMed Central. Unconventional N-H…N Hydrogen Bonds Involving Proline Backbone Nitrogen in Protein Structures
A hydrogen bond forms when a hydrogen attached to an electronegative atom is attracted to a lone pair on a nearby nitrogen. The attraction is mainly electrical, between slightly positive hydrogen and slightly negative nitrogen. No electrons are shared, so nitrogen’s covalent bond count does not change. Hydrogen bonds are drawn dashed, are many times weaker, and shouldn’t be counted when answering “how many bonds.”
For homework, a quick rule covers nearly every case. Neutral nitrogen has three bonds and one lone pair. Positive nitrogen has four bonds and no lone pair. Negative nitrogen has two bonds and two lone pairs.