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Why is mercury the only elemental metal that is liquid at room temperature?

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A periodic table element box for mercury shows its symbol Hg, atomic number 80, atomic weight 200.592, electron configuration, and name. Icons indicate mercury is a transition metal, liquid at room temperature, has a rhombohedral crystal structure, and is weakly basic. — mercury Properties of mercury.

Mercury is the only elemental metal that is liquid at room temperature. While other metals in the zinc group—such as zinc and cadmium—are solids at room temperature, mercury remains liquid due to its unique atomic properties and weak metallic bonding.12

Specifically, mercury has a very low melting point of −38.83 °C (−37.89 °F). While elements like cesium, gallium, and rubidium also have relatively low melting points, they are still higher than standard room temperature. Mercury’s anomalous behavior compared to other metals is further highlighted by its low boiling point and its tendency to form covalent bonds more readily than its group counterparts.12