# How would you explain the ionization energy trend?

Jul 11, 2018

On the basis of $\text{nucular charge}$, and shielding by other electrons....

#### Explanation:

For ionization energy we measure the energy with the transition....

${\text{Atom(g)"+Delta_"ionization energy"rarr"Atom(g)}}^{+} + {e}^{-}$

That is the energy with the formation of one mole of GASEOUS CATIONS, and one mole of GASEOUS ELECTRONS, FROM ONE MOLE of GASEOUS ATOMS....

Two factors influence this ionization energy: (i) the nuclear charge, i.e. ${Z}_{\text{the atomic number}}$; and (ii) shielding by other electrons. Now incomplete electronic shells SHIELD the nuclear charge VERY ineffectively, with the result that ionization energy INCREASES ACROSS THE PERIOD from left to right as we face the Table, BUT DECREASES down a Group, a column of the Periodic Table.

And these trends are reasonable on the basis of simple ideas regarding electrostatics...the valence, the outermost electron, is FARTHER REMOVED FROM the nuclear core, and thus it is MOST LOOSELY held by the parent atom.

And as chemists, as physical scientists, we should look to the data... See...

Are these data consistent with the argument? Why or why not?