Watch a bond slide from covalent to ionic as you change the atoms.
Chemical Bond simulator
This simulation needs a modern browser with canvas support. The measurements and formula below still describe the physics.
Live measurements
Controls
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Formula
ionic % = (1 − e^(−Δχ² / 4)) × 100
- ionic % Ionic character
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- Δχ Electronegativity difference
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Observations
What's happening
Real-world examples
Sodium chloride
Sodium at 0.93 and chlorine at 3.16 differ by 2.23, giving 71% ionic character. A metal and a nonmetal that far apart really do form a lattice rather than molecules.
Hydrogen chloride
The same chlorine against hydrogen differs by 0.96, giving 21% ionic character. For example, that is why HCl is a molecular gas while NaCl is a solid.
Oxygen to oxygen
Two identical atoms have no difference at all, so the pair sits exactly at the midpoint and the bond is 0% ionic. This is the only genuinely nonpolar case.
Hydrogen fluoride
Difference 1.78, which is past the 1.7 cutoff, so the rule says ionic. HF is a molecular gas. Both partners are nonmetals, and this is the case that shows the cutoff is a convention.
Uses of chemical bond
- Deciding whether a compound will dissolve in water or in a nonpolar solvent
- Explaining why sodium chloride forms a lattice while hydrogen chloride is a gas
- Predicting which atom carries the partial negative charge in a reaction
chemical bond pitfalls
- Treating the 1.7 cutoff as a law rather than a convention drawn on a curve
- Calling a nonmetal pair ionic because the difference passed the threshold
- Assuming a polar bond always makes a polar molecule, ignoring geometry
chemical bond questions (8)
What is electronegativity?
Electronegativity measures how strongly an atom pulls a shared pair of electrons toward itself. Pauling's scale runs from caesium at 0.79 to fluorine at 3.98. The number has no units, because it is a comparison rather than a measurement of a quantity. What matters for bonding is never the value itself, only the difference between two of them.
How do you tell if a bond is ionic or covalent?
Take the electronegativity difference between the two atoms. Below 0.4 the bond is called nonpolar covalent, between 0.4 and 1.7 polar covalent, and above 1.7 ionic. However, those numbers are conventions rather than laws. Pauling's relation turns the difference into a percent ionic character on a smooth curve, and reading the percentage tells you more than reading the box.
What is percent ionic character?
It is how far a bond has moved from perfectly shared toward completely transferred, from Pauling's relation: 100 x (1 - e raised to minus the difference squared over 4). Sodium chloride comes out at 71%, hydrogen chloride at 21%. The curve is smooth, therefore no bond suddenly changes nature at any particular difference.
Why is 1.7 the cutoff for an ionic bond?
Because Pauling's curve passes through 50% ionic character at a difference of 1.7. Someone drew the line where the bond is half ionic and half covalent, which is a reasonable place to put it and still an arbitrary one. Move the sliders across that point and watch the percentage change by a fraction while the label jumps.
Why is hydrogen fluoride not ionic?
Its difference is 1.78, past the cutoff, so the rule says ionic. HF is a molecular gas that dissolves to give an acid. The reason is that both hydrogen and fluorine are nonmetals, and two nonmetals share electrons rather than transferring one to form a lattice. This simulator flags any nonmetal pair past the threshold instead of confidently mislabelling it.
What is a partial charge?
In a polar bond the shared pair sits nearer the more electronegative atom, so that atom carries a small negative charge written delta minus, and its partner carries delta plus. These are fractions of an electron rather than whole ones, which is exactly what separates a polar covalent bond from an ionic one where the transfer is complete.
Does a polar bond always make a polar molecule?
No, and this is a common mistake. Carbon dioxide has two strongly polar carbon to oxygen bonds, yet the molecule has no dipole at all, because the bonds point in opposite directions and cancel. Bond polarity is one input; molecular geometry is the other. Work out the bonds first, then the shape.
Why do some elements have no electronegativity value?
Pauling's scale is built from bond energies, so an element that forms no ordinary bonds gets no value. Helium, neon and argon have none, and neither do the synthetic elements past lawrencium. That is a real gap in the scale rather than missing data, so this tool reports no difference instead of defaulting the value to zero.