Interactive periodic table of first ionization energy in kJ/mol and eV. ElementWorks is a free interactive periodic table: hover an element to preview it, click it for its full card, or pick another view from the Show menu.
First ionization energy is the energy needed to remove the outermost electron from a gaseous atom. It generally increases across a period and decreases down a group. Helium has the highest value and the alkali metals are lowest, which is why they lose an electron so easily. Small dips occur from group 2 to group 13 (a p electron is easier to remove than an s electron) and from group 15 to group 16 (electron-electron repulsion in a paired p orbital).
| No. | Symbol | Element | 1st ionization energy (kJ/mol) |
|---|---|---|---|
| 1 | H | Hydrogen | 1312 kJ/mol |
| 2 | He | Helium | 2372 kJ/mol |
| 3 | Li | Lithium | 520 kJ/mol |
| 4 | Be | Beryllium | 900 kJ/mol |
| 5 | B | Boron | 801 kJ/mol |
| 6 | C | Carbon | 1087 kJ/mol |
| 7 | N | Nitrogen | 1402 kJ/mol |
| 8 | O | Oxygen | 1314 kJ/mol |
| 9 | F | Fluorine | 1681 kJ/mol |
| 10 | Ne | Neon | 2081 kJ/mol |
| 11 | Na | Sodium | 496 kJ/mol |
| 12 | Mg | Magnesium | 738 kJ/mol |
| 13 | Al | Aluminium | 577 kJ/mol |
| 14 | Si | Silicon | 787 kJ/mol |
| 15 | P | Phosphorus | 1012 kJ/mol |
| 16 | S | Sulfur | 1000 kJ/mol |
| 17 | Cl | Chlorine | 1251 kJ/mol |
| 18 | Ar | Argon | 1521 kJ/mol |
| 19 | K | Potassium | 419 kJ/mol |
| 20 | Ca | Calcium | 590 kJ/mol |
| 21 | Sc | Scandium | 633 kJ/mol |
| 22 | Ti | Titanium | 659 kJ/mol |
| 23 | V | Vanadium | 651 kJ/mol |
| 24 | Cr | Chromium | 653 kJ/mol |
| 25 | Mn | Manganese | 717 kJ/mol |
| 26 | Fe | Iron | 763 kJ/mol |
| 27 | Co | Cobalt | 760 kJ/mol |
| 28 | Ni | Nickel | 737 kJ/mol |
| 29 | Cu | Copper | 746 kJ/mol |
| 30 | Zn | Zinc | 906 kJ/mol |
| 31 | Ga | Gallium | 579 kJ/mol |
| 32 | Ge | Germanium | 762 kJ/mol |
| 33 | As | Arsenic | 947 kJ/mol |
| 34 | Se | Selenium | 941 kJ/mol |
| 35 | Br | Bromine | 1140 kJ/mol |
| 36 | Kr | Krypton | 1351 kJ/mol |
| 37 | Rb | Rubidium | 403 kJ/mol |
| 38 | Sr | Strontium | 549 kJ/mol |
| 39 | Y | Yttrium | 600 kJ/mol |
| 40 | Zr | Zirconium | 640 kJ/mol |
| 41 | Nb | Niobium | 652 kJ/mol |
| 42 | Mo | Molybdenum | 684 kJ/mol |
| 43 | Tc | Technetium | 702 kJ/mol |
| 44 | Ru | Ruthenium | 710 kJ/mol |
| 45 | Rh | Rhodium | 720 kJ/mol |
| 46 | Pd | Palladium | 804 kJ/mol |
| 47 | Ag | Silver | 731 kJ/mol |
| 48 | Cd | Cadmium | 868 kJ/mol |
| 49 | In | Indium | 558 kJ/mol |
| 50 | Sn | Tin | 709 kJ/mol |
| 51 | Sb | Antimony | 834 kJ/mol |
| 52 | Te | Tellurium | 869 kJ/mol |
| 53 | I | Iodine | 1008 kJ/mol |
| 54 | Xe | Xenon | 1170 kJ/mol |
| 55 | Cs | Cesium | 376 kJ/mol |
| 56 | Ba | Barium | 503 kJ/mol |
| 57 | La | Lanthanum | 538 kJ/mol |
| 58 | Ce | Cerium | 534 kJ/mol |
| 59 | Pr | Praseodymium | 527 kJ/mol |
| 60 | Nd | Neodymium | 533 kJ/mol |
| 61 | Pm | Promethium | 540 kJ/mol |
| 62 | Sm | Samarium | 544 kJ/mol |
| 63 | Eu | Europium | 547 kJ/mol |
| 64 | Gd | Gadolinium | 593 kJ/mol |
| 65 | Tb | Terbium | 566 kJ/mol |
| 66 | Dy | Dysprosium | 573 kJ/mol |
| 67 | Ho | Holmium | 581 kJ/mol |
| 68 | Er | Erbium | 589 kJ/mol |
| 69 | Tm | Thulium | 597 kJ/mol |
| 70 | Yb | Ytterbium | 603 kJ/mol |
| 71 | Lu | Lutetium | 524 kJ/mol |
| 72 | Hf | Hafnium | 659 kJ/mol |
| 73 | Ta | Tantalum | 761 kJ/mol |
| 74 | W | Tungsten | 770 kJ/mol |
| 75 | Re | Rhenium | 760 kJ/mol |
| 76 | Os | Osmium | 840 kJ/mol |
| 77 | Ir | Iridium | 880 kJ/mol |
| 78 | Pt | Platinum | 870 kJ/mol |
| 79 | Au | Gold | 890 kJ/mol |
| 80 | Hg | Mercury | 1007 kJ/mol |
| 81 | Tl | Thallium | 589 kJ/mol |
| 82 | Pb | Lead | 716 kJ/mol |
| 83 | Bi | Bismuth | 703 kJ/mol |
| 84 | Po | Polonium | 812 kJ/mol |
| 85 | At | Astatine | 899 kJ/mol |
| 86 | Rn | Radon | 1037 kJ/mol |
| 87 | Fr | Francium | 380 kJ/mol |
| 88 | Ra | Radium | 509 kJ/mol |
| 89 | Ac | Actinium | 499 kJ/mol |
| 90 | Th | Thorium | 587 kJ/mol |
| 91 | Pa | Protactinium | 568 kJ/mol |
| 92 | U | Uranium | 598 kJ/mol |
| 93 | Np | Neptunium | 604 kJ/mol |
| 94 | Pu | Plutonium | 585 kJ/mol |
| 95 | Am | Americium | 578 kJ/mol |
| 96 | Cm | Curium | 581 kJ/mol |
| 97 | Bk | Berkelium | 601 kJ/mol |
| 98 | Cf | Californium | 608 kJ/mol |
| 99 | Es | Einsteinium | 619 kJ/mol |
| 100 | Fm | Fermium | 627 kJ/mol |
| 101 | Md | Mendelevium | 635 kJ/mol |
| 102 | No | Nobelium | 642 kJ/mol |
| 103 | Lr | Lawrencium | 470 kJ/mol |
| 104 | Rf | Rutherfordium | 580 kJ/mol |
| 105 | Db | Dubnium | — |
| 106 | Sg | Seaborgium | — |
| 107 | Bh | Bohrium | — |
| 108 | Hs | Hassium | — |
| 109 | Mt | Meitnerium | — |
| 110 | Ds | Darmstadtium | — |
| 111 | Rg | Roentgenium | — |
| 112 | Cn | Copernicium | — |
| 113 | Nh | Nihonium | — |
| 114 | Fl | Flerovium | — |
| 115 | Mc | Moscovium | — |
| 116 | Lv | Livermorium | — |
| 117 | Ts | Tennessine | — |
| 118 | Og | Oganesson | — |
The energy required to remove one electron from a neutral gaseous atom. The first ionization energy refers to the outermost electron.
Oxygen has a paired electron in a 2p orbital. The repulsion between the two electrons makes that electron easier to remove than the unpaired electrons in nitrogen.
The alkali metals, with cesium lowest among elements with reliable data. Their single outer electron is far from the nucleus and well shielded.
© 2026 Prof. Rami El Oweini. All rights reserved.