The Difference Between an Element Group and Period

The Difference Between an Element Group and Period 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)