Why is bromine liquid at room temperature while chlorine and iodine are not?
Quick Answer
Bromine sits in between chlorine and iodine, so its molecules have intermolecular forces strong enough to make it a liquid, but not strong enough to make a solid at room temperature. Its molecular size puts it between the two extremes.
The Full Story
Bromine is unusual because it is one of the few elements that is liquid at room temperature, along with mercury. In the halogen group, chlorine is a gas and iodine is a solid, but bromine falls in between because its Br2 molecules have intermediate size and intermolecular attractions. Those forces are strong enough to keep bromine from evaporating like chlorine, yet not so strong that it freezes at ordinary temperatures. This makes bromine a useful example of how periodic trends affect physical state.
Key Facts
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