# Of these elements, which has the greatest first ionization energy? Why? Ce, C, Cl, Ca, Cs.

Jun 4, 2016

Quite possibly chlorine.

#### Explanation:

Ionization energy is the energy associated with the reaction:

"Element(g) "rarr " (Element")^+(g) + e^-

Ionization energy increases across a Period (from left to right), and decreases down a Group. Why does this trend make sense intuitively?

As physical scientists we should always consider the data. See this link.

Note that we consider atomic (NOT molecular) properties.