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What element has the lowest first ionization energy?

Answer 1

The general trend on the periodic table indicates that ionization energy decreases down a period as the average distance of the electron from the nucleus increases and the screening by inner electrons increases with the addition of electrons to higher octets. This means that the electrons are easier to remove because the nucleus is not holding them as tightly.

Because atoms on the left side of the periodic table are more willing to give up electrons in order to reach a noble gas configuration—a configuration that is more easily reached by losing electrons than by gaining them—ionization energy likewise decreases from right to left.

It would make sense, given the trend, for the lowest, leftmost element—Francium—to have the lowest first ionization energy.

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Answer 2

Wyatt Adkins

Helium.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.