Internuclear distance is the distance between the nuclei of two bonded (or interacting) atoms. In AP Chem, it's the x-axis of the potential energy diagram in Topic 2.2, where the minimum of the curve marks the equilibrium bond length and the depth of that well equals the bond energy.
Internuclear distance is exactly what it sounds like, the separation between the nuclei of two atoms. It matters because atoms feel competing Coulombic forces as they approach each other. Each nucleus attracts the other atom's electrons, but the two nuclei (and the two electron clouds) repel each other. The balance between attraction and repulsion changes as the distance changes, and that's what the famous potential energy curve shows.
Per the CED (2.2.A.1), a graph of potential energy versus internuclear distance is the go-to representation for atomic interactions. Read it like this. Far apart, the atoms barely interact and potential energy is near zero. As they get closer, attraction dominates and potential energy drops. At one specific distance the energy hits its lowest point. That distance is the equilibrium bond length, and the depth of the well is the bond energy (how much energy you'd need to pull the atoms apart). Squeeze the atoms closer than that, and nucleus-nucleus repulsion takes over, so the curve shoots up steeply.
This term lives in Unit 2: Compound Structure and Properties, Topic 2.2 (Intramolecular Force and Potential Energy) and directly supports learning objective 2.2.A, which asks you to represent the relationship between potential energy and the distance between atoms. Internuclear distance is the variable everything else hangs on. Bond length, bond energy, and bond order all get read off a PE vs. internuclear distance graph. The CED also ties bond length to atom size and bond order (2.2.A.2): triple bonds pull nuclei closer than single bonds, so higher bond order means shorter distance and a deeper energy well. If you can interpret this one graph, you've unlocked a chunk of Unit 2.
Keep studying AP Chemistry Unit 2
Bond Length (Unit 2)
Bond length is the special internuclear distance where potential energy bottoms out. Every bond length is an internuclear distance, but not every internuclear distance is a bond length. Atoms vibrate around this sweet spot.
Coulomb's Law (Units 1-2)
Coulomb's law explains the whole shape of the PE curve. Attraction and repulsion both depend on charge and distance, and internuclear distance is the distance in that equation. Smaller distance plus higher effective charge means a stronger, lower-energy bond.
Atomic Radius (Unit 1)
Bigger atoms have bigger cores, which keeps their nuclei farther apart. That's why H-I has a longer equilibrium internuclear distance than H-F. Periodic trends from Unit 1 predict bond lengths in Unit 2.
Single Bond vs. Triple Bond (Unit 2)
More shared electron pairs pull nuclei closer together. A triple bond between the same two atoms has a shorter internuclear distance and a larger bond energy than a single bond, which is exactly what EK 2.2.A.2 wants you to know.
This term shows up almost exclusively through the potential energy diagram. Multiple-choice questions hand you a PE vs. internuclear distance graph (or describe one) and ask what the minimum represents, what happens if the atoms are compressed below equilibrium (repulsive forces dominate and potential energy rises sharply), or which curve belongs to a stronger or shorter bond. You might also get energy bookkeeping, like a bond with 450 kJ/mol bond energy absorbing 300 kJ/mol, where you have to recognize the bond stretches but doesn't break. On FRQs, the concept supports bond energy reasoning. The 2023 free-response exam, for example, asked about breaking all the Al-Cl bonds in gaseous AlCl₃, which is just climbing out of the potential energy well three times. Be ready to sketch the curve, label equilibrium bond length and bond energy, and justify comparisons using Coulomb's law.
Internuclear distance is a variable, any separation between two nuclei, from squished together to infinitely far apart. Bond length is one specific value of that variable, the equilibrium distance where potential energy is at its minimum. On the graph, internuclear distance is the entire x-axis; bond length is the x-coordinate of the lowest point.
Internuclear distance is the distance between two atoms' nuclei, and it's the x-axis of the potential energy diagram in Topic 2.2.
The minimum of the potential energy curve marks the equilibrium bond length, and the depth of that well equals the bond energy.
At distances shorter than the equilibrium bond length, nucleus-nucleus repulsion dominates and potential energy rises steeply.
Higher bond order means a shorter internuclear distance and a larger bond energy, so a triple bond is shorter and stronger than a single bond between the same atoms.
Larger atoms (bigger cores) bond at longer internuclear distances, connecting Unit 1 atomic radius trends to Unit 2 bond properties.
Coulomb's law explains the curve's shape, since both attraction and repulsion between charged particles depend on distance.
It's the distance between the nuclei of two atoms. AP Chem uses it as the x-axis of the potential energy diagram in Topic 2.2, where the energy minimum identifies the equilibrium bond length and bond energy.
Not exactly. Internuclear distance is any separation between two nuclei, while bond length is the specific internuclear distance where potential energy is lowest. For H₂, that equilibrium distance is about 74 pm.
Below the equilibrium bond length, repulsion between the two positively charged nuclei (and between the electron clouds) overwhelms attraction. That's why the curve shoots up steeply on the left side of the graph.
No. If a bond has a bond energy of 450 kJ/mol and absorbs only 300 kJ/mol, the atoms vibrate at a larger internuclear distance but stay bonded. The bond only breaks when the absorbed energy equals or exceeds the bond energy.
More shared electron pairs sit between the nuclei, increasing the attraction that pulls them together. Per EK 2.2.A.2, higher bond order means shorter bond length and larger bond energy.