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How do bonding strength and thermal expansion relate in crystals?

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Two diagrams show the three-dimensional structure of a methane molecule: panel A uses a ball-and-stick model with a central carbon atom connected to four hydrogen atoms in a tetrahedral arrangement, while panel B illustrates the bond angle of 109.5 degrees and bond length of 1.09 angstroms between carbon and hydrogen atoms. — chemical compound Methane, in which four hydrogen atoms are bound to a single carbon atom, is an example of a basic chemical compound. The structures of chemical compounds are influenced by complex factors, such as bond angles and bond length.

In crystalline solids, the relationship between bonding strength and thermal expansion is inverse: as the strength of the chemical bonds holding the atoms together increases, the coefficient of thermal expansion typically decreases.1

This occurs because thermal expansion is governed by a dynamic balance between the cohesive forces of the crystal lattice and the thermal energy introduced by temperature changes. In a crystal, atoms are held in equilibrium positions by mutual electrical forces that act similarly to springs. When temperature increases, these atoms vibrate with greater amplitude, requiring more distance between them.23

Materials with stronger bonding forces require significantly more heat to overcome those cohesive forces and increase the interatomic distance. Consequently, crystals with strong bonds—such as periclase—exhibit higher melting points and lower rates of expansion compared to materials with weaker bonds, such as halite.1