Periodic Table Periods

A period on the periodic table is a row of chemical elements. All elements in a row have the same number of electron shells. Each next element in a period has one more proton and is less metallic than its predecessor. Arranged this way, elements in the same group (column) have similar chemical and physical properties, reflecting the periodic law. For example, the halogens lie in the second-to-last group (group 17) and share similar properties, such as high reactivity and the tendency to gain one electron to arrive at a noble-gas electronic configuration. As of 2022, a total of 118 elements have been discovered and confirmed.

Name by element lith­ium group beryl­lium group scan­dium group titan­ium group vana­dium group chro­mium group man­ga­nese group iron group co­balt group nickel group cop­per group zinc group boron group car­bon group nitro­gen group oxy­gen group fluor­ine group helium orneon group
Period 1 H He
Period 2 Li Be B C N O F Ne
Period 3 Na Mg Al Si P S Cl Ar
Period 4 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
Period 5 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe
Period 6 Cs Ba La–Yb Lu Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn
Period 7 Fr Ra Ac–No Lr Rf Db Sg Bh Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Og

Period 1

The first period contains fewer elements than any other, with only two, hydrogen and helium. They therefore do not follow the octet rule, but rather a duplet rule. Chemically, helium behaves like a noble gas, and thus is taken to be part of the group 18 elements. However, in terms of its nuclear structure it belongs to the s-block, and is therefore sometimes classified as a group 2 element, or simultaneously both 2 and 18. Hydrogen readily loses and gains an electron, and so behaves chemically as both a group 1 and a group 17 element.

Group 1 18
Atomic # 1 2
Name H He

Period 2

Period 2 elements involve the 2s and 2p orbitals. They include the biologically most essential elements besides hydrogen: carbon, nitrogen, and oxygen.

Group 1 2 13 14 15 16 17 18
Atomic # 3 4 5 6 7 8 9 10
Name Li Be B C N O F Ne

Period 3

All period three elements occur in nature and have at least one stable isotope. All but the noble gas argon are essential to basic geology and biology.

Group 1 2 13 14 15 16 17 18
Atomic # 11 12 13 14 15 16 17 18
Name Na Mg Al Si P S Cl Ar

Period 4

Period 4 includes the biologically essential elements potassium and calcium, and is the first period in the d-block with the lighter transition metals. These include iron, the heaviest element forged in main-sequence stars and a principal component of the Earth, as well as other important metals such as cobalt, nickel, and copper. Almost all have biological roles. Completing the fourth period are six p-block elements: gallium, germanium, arsenic, selenium, bromine, and krypton.

Group 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Atomic # 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36
Name K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr

Period 5

Period 5 has the same number of elements as period 4 and follows the same general structure but with one more post transition metal and one fewer nonmetal. Of the three heaviest elements with biological roles, two (molybdenum and iodine) are in this period; tungsten, in period 6, is heavier, along with several of the early lanthanides. Period 5 also includes technetium, the lightest exclusively radioactive element.

Group 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Atomic # 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54
Name Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe

Period 6

Period 6 is the first period to include the f-block, with the lanthanides (also known as the rare earth elements), and includes the heaviest stable elements. Many of these heavy metals are toxic and some are radioactive, but platinum and gold are largely inert.

Group 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Atomic # 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86
Name Cs Ba La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn

Period 7

All elements of period 7 are radioactive. This period contains the heaviest element which occurs naturally on Earth, plutonium. All of the subsequent elements in the period have been synthesized artificially. Whilst five of these (from americium to einsteinium) are now available in macroscopic quantities, most are extremely rare, having only been prepared in microgram amounts or less. Some of the later elements have only ever been identified in laboratories in quantities of a few atoms at a time.

Although the rarity of many of these elements means that experimental results are not very extensive, periodic and group trends in behavior appear to be less well defined for period 7 than for other periods. Whilst francium and radium do show typical properties of groups 1 and 2, respectively, the actinides display a much greater variety of behavior and oxidation states than the lanthanides. These peculiarities of period 7 may be due to a variety of factors, including a large degree of spin–orbit coupling and relativistic effects, ultimately caused by the very high positive electrical charge from their massive atomic nuclei.

Group 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Atomic # 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118
Name Fr Ra Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr Rf Db Sg Bh Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Og
Sabalico Logo
Sabalytics Logo
Senty Logo
SEO Guide Logo
World Map Logo
rStatistics Logo
Day Map Logo
Time Zone Logo
Galaxy View Logo
Periodic Table Logo
My Location Logo
Weather Track Logo
Sprite Sheet Logo
Barcode Generator Logo
Test Speed Logo
Website Tools Logo
Image Tools Logo
Color Tools Logo
Text Tools Logo
Finance Tools Logo
File Tools Logo
Data Tools Logo
History of Humanity - History Archive Logo
History of Humanity - History Mysteries Logo
History of Humanity - Ancient Mesopotamia Logo
History of Humanity - Persian Empire Logo
History of Humanity - Alexander the Great Logo
History of Humanity - Roman History Logo
History of Humanity - Punic Wars Logo
History of Humanity - Golden Age of Piracy Logo
History of Humanity - Revolutionary War Logo