To determine the number of valence electrons in a molecule like hydrogen chloride (HCl), we need to consider the valence electron count of each atom and their respective charges.
Hydrogen (H) is in Group 1 of the periodic table and has 1 valence electron.
Chlorine (Cl) is in Group 17 of the periodic table and has 7 valence electrons.
In the case of hydrogen chloride (HCl), there is a single bond between the hydrogen and chlorine atoms, resulting in the sharing of one electron pair.
Thus, the total number of valence electrons in hydrogen chloride is 1 (from hydrogen) + 7 (from chlorine) = 8 valence electrons.
It's worth noting that chlorine (Cl) typically prefers to complete its octet by gaining one electron, forming a chloride ion (Cl-) with a full outer shell. In this case, the valence electron count of chloride would be 8. However, in the context of a molecule like hydrogen chloride, where chlorine shares one electron pair with hydrogen, it is considered to have 7 valence electrons.