The Difference Between an Element Group and Period

Table of elements as seen from a side angle.

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Groups and periods are two ways of categorizing elements in the periodic table. Periods are horizontal rows (across) the periodic table, while groups are vertical columns (down) the table. Atomic number increases as you move down a group or across a period.

Element Groups

Elements in a group share a common number of valence electrons. For example, all of the elements in the alkaline earth group have a valence of two. Elements belonging to a group typically share several common properties.

The groups in the periodic table go by a variety of different names:

IUPAC Name Common Name Family Old IUPAC CAS notes
Group 1 alkali metals lithium family IA IA excluding hydrogen
Group 2 alkaline earth metals beryllium family IIA IIA  
Group 3   scandium family IIIA IIIB  
Group 4   titanium family IVA IVB  
Group 5   vanadium family VA VB  
Group 6   chromium family VIA VIB  
Group 7   manganese family VIIA VIIB  
Group 8   iron family VIII VIIIB  
Group 9   cobalt family VIII VIIIB  
Group 10   nickel family VIII VIIIB  
Group 11 coinage metals copper family IB IB  
Group 12 volatile metals zinc family IIB IIB  
Group 13 icoasagens boron family IIIB IIIA  
Group 14 tetrels, crystallogens carbon family IVB IVA tetrels from the Greek tetra for four
Group 15 pentels, pnictogens nitrogen family VB VA pentels from the Greek penta for five
Group 16 chalcogens oxygen family VIB VIA  
Group 17 halogens fluorine family VIIB VIIA  
Group 18 noble gases, aerogens helium family or neon family Group 0 VIIIA  

Another way to group elements is based on their shared properties (in some cases, these groupings do not correspond to the columns in the periodic table). Such groups include alkali metals, alkaline earth metals, transition metals (including rare earth elements or lanthanides and also actinides), basic metals, metalloids or semimetals, nonmetals, halogens, and noble gases. Within this classification system, hydrogen is a nonmetal. The nonmetals, halogens, and noble gases are all types of nonmetallic elements. The metalloids have intermediate properties. All of the other elements are metallic.

Element Periods

Elements in a period share the highest unexcited electron energy level. There are more elements in some periods than others because the number of elements is determined by the number of electrons allowed in each energy sub-level.

There are seven periods for naturally occurring elements:

  • Period 1: H, He (does not follow the octet rule)
  • Period 2: Li, Be, B, C, N, O, F, Ne (involves s and p orbitals)
  • Period 3: Na, Mg, Al, Si, P, S, Cl, Ar (all have at least 1 stable isotope)
  • Period 4: K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Br, Kr (first period with d-block elements)
  • Period 5: Rb, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sn, Te, I, Xe (same number of elements as period 4, same general structure, and includes first exclusively radioactive element, Tc)
  • Period 6: 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 (first period with f-block elements)
  • Period 7: Fr, Ra, Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No, Lr, Rd, Db, Sg, Bh, Hs, Mt, Ds, Rg, Cn, Uut, Fl, Uup, Lv, Uus, Uuo (all elements are radioactive; contains heaviest natural elements)