Atomic spacing refers to the distance between thenuclei ofatoms in a material. This space is extremely large compared to thesize of theatomic nucleus, and is related to thechemical bonds which bind atoms together.^[1] In solid materials, the atomic spacing is described by thebond lengths of its atoms. In ordered solids, the atomic spacing between two bonded atoms is generally around a fewångströms (Å), which is on the order of 10⁻¹⁰ meters (seeLattice constant). However, in very low density gases (for example, inouter space) the average distance between atoms can be as large as ameter. In this case, the atomic spacing is not referring to bond length.

The atomic spacing of crystalline structures is usually determined by passing anelectromagnetic wave of knownfrequency through the material, and using the laws ofdiffraction to determine its atomic spacing. The atomic spacing ofamorphous materials (such asglass) varies substantially between different pairs of atoms, therefore diffraction cannot be used to accurately determine atomic spacing. In this case, the average bond length is a common way of expressing the distance between its atoms.^{[citation needed]}

Bond length can be determined between different elements in molecules by using theatomic radii of the atoms.Carbon bonds with itself to form two covalent network solids.^[2]Diamond's C-C bond has a distance of${\displaystyle \frac{\sqrt{3}a}{4}\approx 0.154\text{nm}}$ away from each carbon since${\displaystyle a_{\text{diamond}}\approx 0.357\text{nm}}$, whilegraphite's C-C bond has a distance of${\displaystyle \frac{a}{\sqrt{3}}\approx 0.142\text{nm}}$ away from each carbon since${\displaystyle a_{\text{graphite}}\approx 0.246\text{nm}}$. Although both bonds are between the same pair of elements they can have different bond lengths.^[3]

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