Ionization Energy

Ionization energy, also called ionization potential, is the energy necessary to remove an electron from the neutral atom.

X + energy → X+ + e

where X is any atom or molecule capable of being ionized, X+ is that atom or molecule with an electron removed (positive ion), and e is the removed electron.

A nitrogen atom, for example, requires the following ionization energy to remove the outermost electron.

N + IE → N+ + e        IE = 14.5 eV

The ionization energy associated with removal of the first electron is most commonly used. The nth ionization energy refers to the amount of energy required to remove an electron from the species with a charge of (n-1).

1st ionization energy

X → X+ + e

2nd ionization energy

X+ → X2+ + e

3rd ionization energy

X2+ → X3+ + e

Ionization Energy for different Elements

There is an ionization energy for each successive electron removed. The electrons that circle the nucleus move in fairly well-defined orbits. Some of these electrons are more tightly bound in the atom than others. For example, only 7.38 eV is required to remove the outermost electron from a lead atom, while 88,000 eV is required to remove the innermost electron. Helps to understand reactivity of elements (especially metals, which lose electrons).

In general, the ionization energy increases moving up a group and moving left to right across a period. Moreover:

  • Ionization energy is lowest for the alkali metals which have a single electron outside a closed shell.
  • Ionization energy increases across a row on the periodic maximum for the noble gases which have closed shells

For example, sodium requires only 496 kJ/mol or 5.14 eV/atom to ionize it. On the other hand neon, the noble gas, immediately preceding it in the periodic table, requires 2081 kJ/mol or 21.56 eV/atom.

Ionization energy

Source: wikipedia.org License: CC BY-SA 3.0

Periodic Table

Hydro­gen1H He­lium2He
Lith­ium3Li Beryl­lium4Be Boron5B Carbon6C Nitro­gen7N Oxy­gen8O Fluor­ine9F Neon10Ne
So­dium11Na Magne­sium12Mg Alumin­ium13Al Sili­con14Si Phos­phorus15P Sulfur16S Chlor­ine17Cl Argon18Ar
Potas­sium19K Cal­cium20Ca Scan­dium21Sc Tita­nium22Ti Vana­dium23V Chrom­ium24Cr Manga­nese25Mn Iron26Fe Cobalt27Co Nickel28Ni Copper29Cu Zinc30Zn Gallium31Ga Germa­nium32Ge Arsenic33As Sele­nium34Se Bromine35Br Kryp­ton36Kr
Rubid­ium37Rb Stront­ium38Sr Yttrium39Y Zirco­nium40Zr Nio­bium41Nb Molyb­denum42Mo Tech­netium43Tc Ruthe­nium44Ru Rho­dium45Rh Pallad­ium46Pd Silver47Ag Cad­mium48Cd Indium49In Tin50Sn Anti­mony51Sb Tellur­ium52Te Iodine53I Xenon54Xe
Cae­sium55Cs Ba­rium56Ba Lan­thanum57La 1 asterisk Haf­nium72Hf Tanta­lum73Ta Tung­sten74W Rhe­nium75Re Os­mium76Os Iridium77Ir Plat­inum78Pt Gold79Au Mer­cury80Hg Thallium81Tl Lead82Pb Bis­muth83Bi Polo­nium84Po Asta­tine85At Radon86Rn
Fran­cium87Fr Ra­dium88Ra Actin­ium89Ac 1 asterisk Ruther­fordium104Rf Dub­nium105Db Sea­borgium106Sg Bohr­ium107Bh Has­sium108Hs Meit­nerium109Mt Darm­stadtium110Ds Roent­genium111Rg Coper­nicium112Cn Nihon­ium113Nh Flerov­ium114Fl Moscov­ium115Mc Liver­morium116Lv Tenness­ine117Ts Oga­nesson118Og
1 asterisk Cerium58Ce Praseo­dymium59Pr Neo­dymium60Nd Prome­thium61Pm Sama­rium62Sm Europ­ium63Eu Gadolin­ium64Gd Ter­bium65Tb Dyspro­sium66Dy Hol­mium67Ho Erbium68Er Thulium69Tm Ytter­bium70Yb Lute­tium71Lu
1 asterisk Thor­ium90Th Protac­tinium91Pa Ura­nium92U Neptu­nium93Np Pluto­nium94Pu Ameri­cium95Am Curium96Cm Berkel­ium97Bk Califor­nium98Cf Einstei­nium99Es Fer­mium100Fm Mende­levium101Md Nobel­ium102No Lawren­cium103Lr


Nuclear and Reactor Physics:

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Advanced Reactor Physics:

  1. K. O. Ott, W. A. Bezella, Introductory Nuclear Reactor Statics, American Nuclear Society, Revised edition (1989), 1989, ISBN: 0-894-48033-2.
  2. K. O. Ott, R. J. Neuhold, Introductory Nuclear Reactor Dynamics, American Nuclear Society, 1985, ISBN: 0-894-48029-4.
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  4. E. E. Lewis, W. F. Miller, Computational Methods of Neutron Transport, American Nuclear Society, 1993, ISBN: 0-894-48452-4.

See above: