Which of the following properties increase with increasing atomic number for fluorine and chlorine?

I. melting point of the elements (yes)
II. boiling point of the hydrogen halides

i'm not sure about II because HF has the highest boiling point but fluorine and chloride fit in the general trend that increasing atomic number results in increasing boiling points. help? Is it both, just one, or neither?

See your post above.

To determine whether both or neither of the properties increase with increasing atomic number for fluorine and chlorine, we need to examine their characteristics.

I. Melting point of the elements:
In general, as atomic number increases within a group or period, the melting point of the elements tends to increase. This is because higher atomic number typically corresponds to an increase in atomic size and stronger intermolecular forces, resulting in higher melting points. For fluorine and chlorine, where both elements belong to the same group (Group 17, or the halogens), their atomic number increases from fluorine (9) to chlorine (17). Therefore, based on the general trend, the melting point of the elements will increase with increasing atomic number. So, option I is correct.

II. Boiling point of the hydrogen halides:
Hydrogen halides include hydrogen fluoride (HF), hydrogen chloride (HCl), hydrogen bromide (HBr), and hydrogen iodide (HI). The boiling points of these compounds generally increase with increasing atomic number of the halogen atom involved. However, there are exceptions due to factors such as hydrogen bonding.

In this case, you mentioned that HF has the highest boiling point, which is contrary to the expected trend. This can be explained by the presence of hydrogen bonding in HF. Hydrogen bonding is a strong intermolecular force that occurs when hydrogen is directly bonded to a highly electronegative atom (such as fluorine, oxygen, or nitrogen). The electronegativity difference between hydrogen and fluorine promotes a strong dipole-dipole interaction, resulting in higher boiling points for HF compared to the other hydrogen halides.

Therefore, based on the exception in the boiling point trend caused by hydrogen bonding in HF, we can conclude that option II is not correct. The boiling points of hydrogen halides generally increase with the increasing atomic number of the halogen, except for the specific case of HF due to hydrogen bonding.