First ionization energies of Hydrogen and Chlorine

[21385]

The EK1001 book says that Chlorine has the higher one because it is more non-metal than hydrogen. However, data shows otherwise. How would I approach a question like this on the mcat test?

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[venacontracta]

Ionization energy increases bottom to top and left to right on the periodic table. The reasoning behind this has to do with effective nuclear charge, Zeff. Any exceptions to this are exceptions to the general trend which will not be tested on the MCAT.