Final answer:
Halogens have different physical states at room temperature due to varying strengths of dispersion forces attributed to differences in molecular size and mass. Fluorine and chlorine are gases, bromine is a liquid, and iodine is a solid because the larger and heavier the molecule, the stronger the dispersion forces.
Step-by-step explanation:
Physical States of Halogens at Room Temperature
The physical states of halogens at room temperature can be explained by their atomic size and the resulting strength of dispersion forces. As atoms increase in size and mass from fluorine to iodine, the strength of their dispersion forces also increases. Fluorine (F2) and chlorine (Cl2) are relatively small halogens and thus exhibit weaker dispersion forces, making them gases at room temperature. In contrast, bromine (Br2), with larger atoms, exhibits stronger dispersion forces sufficient to be a liquid. Iodine (I2), with the largest atoms among these, has the strongest dispersion forces, leading to its solid state at room temperature. Therefore, the trend in the physical states from gas to solid among these halogens is due to an increase in dispersion forces corresponding to the increase in molecular mass from F2 to I2.
Interestingly, this variation in physical states also aligns with variations in melting and boiling points for the halogens, with higher boiling points for the larger and heavier molecules. The physical properties of these elements at room temperature are a direct consequence of the strength of their intermolecular forces.