* Chlorine (Cl₂): Chlorine is a gas at room temperature because its molecules are held together by weak van der Waals forces. These forces arise from temporary fluctuations in electron distribution around the molecule, resulting in weak attractions. Because these forces are weak, chlorine molecules are easily separated and exist as a gas.
* Bromine (Br₂): Bromine is a liquid at room temperature because its molecules have stronger van der Waals forces compared to chlorine. This is due to the larger size of bromine atoms, which leads to greater electron cloud fluctuations and stronger temporary dipoles.
* Iodine (I₂): Iodine is a solid at room temperature because its molecules experience the strongest van der Waals forces among the three halogens. Iodine atoms are even larger than bromine atoms, resulting in even stronger temporary dipoles and stronger attractions between molecules.
Key takeaway: As you move down the halogen group, the size of the atoms increases, leading to stronger van der Waals forces and a shift from gaseous to liquid to solid states at room temperature.
