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
A) I only
B) II only
C) Both I and II
D) neither I nor II
I think it's A - is that right?
Yes, HF has a higher boilng point than HCl. It has something to do with a larger dipole moment and intramolecular binding.
http://www.physicsforums.com/showthread.php?t=179100
To determine the correct answer, we need to analyze the properties of fluorine and chlorine in relation to their atomic numbers.
I. Melting Point: The melting point generally increases with increasing atomic number because as atomic number increases, there are more electrons and stronger intermolecular forces. This results in a higher amount of energy required to break the bonds between the molecules, leading to a higher melting point.
II. Boiling Point of Hydrogen Halides: The boiling point of hydrogen halides generally decreases with increasing atomic number because, in these compounds, hydrogen forms a covalent bond with the halogen atom (fluorine, chlorine, bromine, iodine). As the atomic number increases, the size of the halogen atom increases. Therefore, the bond between hydrogen and the larger halogen atom becomes weaker, resulting in a lower boiling point.
Based on the above explanations, the correct answer is option A) I only. The melting point increases with increasing atomic number for fluorine and chlorine, but the boiling point of hydrogen halides does not follow this pattern.