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?
In the series HI, HBr, HCl, HF, the boiling point decreases because the molar mass is decreasing; however, HF (remember F has the highest electronegativity of any element) has hydrogen bond which RAISES the boiling point of HF. H2O, NH3, HF are in the same category. HF should be a gas, H2O should be a gas but they aren't because of H bonding. NH3 IS a gas BUT the boiling point is much higher than it should be (from the trend) SbH3, AsH3, PH3, NH3.
Which answer is it then? I feel like it's just I because HF is an exception.
To determine which properties increase with increasing atomic number for fluorine and chlorine, we will need to examine the periodic trends for these elements.
I. Melting Point: In general, the melting point of elements tends to increase with increasing atomic number within a group. This is because as atomic number increases, the atoms have more electrons and a higher positive charge in the nucleus, resulting in stronger intermolecular forces and higher melting points.
Fluorine and chlorine both belong to Group 17 (Group VIIA), which is known as the halogens. Within this group, the melting points generally increase down the group. Consequently, as fluorine has a smaller atomic number, it will have a lower melting point compared to chlorine since chlorine has a higher atomic number within the group.
Therefore, for the first statement, it is true that the melting points of fluorine and chlorine increase with increasing atomic number.
II. Boiling Point of Hydrogen Halides: The boiling points of hydrogen halides generally follow the same trend as the melting points of the halogens. However, there are some exceptions due to differences in molecular structure and intermolecular forces.
Hydrogen fluoride (HF), which corresponds to fluorine, actually has a higher boiling point compared to the other hydrogen halides (HCl, HBr, and HI). This can be attributed to the presence of hydrogen bonding in HF, which is stronger than the van der Waals forces present in the other hydrogen halides.
Therefore, for the second statement, it is true that the boiling point trend for the hydrogen halides does not strictly follow the trend of increasing atomic number. While fluorine (HF) has the highest boiling point, the trend for chlorine (HCl) and the other hydrogen halides does generally follow the increasing boiling point trend with increasing atomic number.
In summary, for the given properties:
I. Melting point: Increases with increasing atomic number for fluorine and chlorine.
II. Boiling point of hydrogen halides: Generally follows the trend, but with an exception for fluorine (HF).