Final answer:
Chlorine has a higher ionization energy than sulfur because it is further to the right on the periodic table, resulting in a stronger attraction between the nucleus and valence electrons due to a higher effective nuclear charge.
Step-by-step explanation:
The question asked is why sulfur has an ionization energy of 1005 kJ/mol whereas chlorine has a higher ionization energy of 1255 kJ/mol. This can be explained by atomic structure and Coulomb's law. As you move across a period in the periodic table, ionization energies increase. This is because the atomic size decreases, resulting in a stronger electrostatic attraction between the nucleus and the valence electrons, making it more difficult to remove an electron. Chlorine is to the right of sulfur in the periodic table, indicating it has a higher effective nuclear charge, which leads to a higher ionization energy consistent with this general trend.