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Ionization Energy The energy required to remove an electron from a gaseous

atom or ion. The electron is completely removed from the atom.

Z+

Z-

Z+

(Z-1)-

e-+ E

Ionization requires an input of energy...we must provide energy to separate the negatively-charged electron from the positively-charged nucleus.

E + X X+ + e-

The greater the ability of an

atom to hold on to its

electrons, the higher the

ionization energy will be.

Generally performed using photons, with energy measured in electronvolts, eV (1 eV = 1.6 x 10-19 J).

Ionization Examples

Lets compare the energies required to remove valence versus core electrons.

Na(g) Na+(g) + e- IE1

= 5.14 eV

Na+(g) Na2+(g) + e- IE2

= 47.3 eV

Takes significantly more energy to remove a core electron. core electron configurations tend to be energetically stable.

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First Ionization E Trends

IE increases from left to

right across a period.

IE decreases from top to

bottom down a group.

Reason: increasing Z+ (the number of

protons in the nucleus) which attracts

the valence electron

Reason: increasing distance between

electron and nucleus