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Why is the first ionization energy of boron LESS than that of beryllium? Boron has a higher atomic number.

Answer 1

Consider electronic configurations of #Be# versus #B#. Should a #p# electron be easier to remove?

#Be, Z=4, 1s^(2)2s^2.#

#B, Z=5, 1s^(2)2s^(2)2p^1.#

A priori , should it be easier to remove a #p-#orbital electron, which by definition has zero electron density at the nucleus? An #s-#orbital electron, even those of the #2s# shell has some probability density at or near the nucleus, and this probably accounts for the differential ionization energies.

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Answer 2

Owen Ambrose

The first ionization energy of boron is less than that of beryllium because boron has an electron in a higher energy level (2p) compared to beryllium (2s), which experiences greater shielding from the nucleus, leading to easier removal of the outer electron in boron.

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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.