Chlorine, Cl2, is a gas at room temperature, but bromine, Br2, is a liquid. Why?

Chlorine would create a nonpolar covalent bond as each atom (with equal electronegativity) shared it's non paired electron. Nonpolar molecules have a very weak attraction to other nonpolar molecules, so a lower boiling point would result.

Wouldn't bromine do the same thing, since it also has one unpaired electron?

Yes but the mass of a mole of Br2 is about 160 versus that of a mole of Cl2 of about 71. Big difference. Note the trend in group 17 (or VIIA depending upon the system you are using). F2 and Cl2 are gases. Br2 is a liquid. I2 is a solid.

Ah, bromine, the liquid joker of the periodic table! You see, bromine may have an unpaired electron, but it has other tricks up its sleeve that make it a liquid at room temperature. Unlike chlorine, bromine atoms are larger and have more electrons, which creates a stronger van der Waals force between the molecules. This force helps hold the bromine molecules together, making it harder to break them apart into a gaseous state. So, while chlorine likes to gas it up, bromine prefers to bring the liquid vibes to the party!

While it is true that both chlorine and bromine have one unpaired electron, which allows them to form nonpolar covalent bonds, there are other factors that determine whether a substance is a gas or a liquid at room temperature.

The main factor is the strength of the intermolecular forces between the molecules. In the case of chlorine, the intermolecular forces are relatively weak because it is a small molecule with only two atoms. This weak interaction between chlorine molecules allows them to easily break apart and move freely as a gas at room temperature.

On the other hand, bromine is a larger molecule with more electrons, which results in stronger intermolecular forces. The additional electrons in bromine create stronger London dispersion forces, also known as van der Waals forces, which cause the bromine molecules to attract each other more strongly. As a result, bromine remains as a liquid at room temperature due to the stronger intermolecular forces that hold the molecules together.

So, even though both chlorine and bromine can form nonpolar covalent bonds, the difference in their molecular sizes and the strength of intermolecular forces account for the difference in their states at room temperature.

Actually, the reason for the different states of chlorine and bromine at room temperature is related to their molecular structure and intermolecular forces.

While both chlorine (Cl2) and bromine (Br2) have similar electronic configurations with one unpaired electron each, their molecular sizes and intermolecular forces differ.

Chlorine molecules are smaller in size compared to bromine molecules. The smaller size of chlorine atoms allows for closer packing of the molecules, resulting in stronger intermolecular forces called London dispersion forces. These forces occur due to temporary fluctuations in electron distribution, causing instantaneous temporary dipoles that can induce dipoles in neighboring molecules, leading to an attractive force. This results in chlorine molecules being attracted to one another more strongly, requiring a higher amount of energy (higher boiling point) to break these intermolecular forces and convert chlorine into a gas at room temperature.

On the other hand, bromine atoms are larger in size, resulting in weaker intermolecular forces. Although bromine also experiences London dispersion forces, the larger size of bromine atoms makes it more difficult for these forces to hold the molecules together tightly. As a result, it requires less energy (lower boiling point) to overcome these weaker forces and convert bromine into a liquid at room temperature.

So, even though both chlorine and bromine have one unpaired electron and share similar covalent bonding, the difference in their molecular sizes and resulting intermolecular forces is what causes chlorine to exist as a gas at room temperature and bromine as a liquid.