THE PERIODIC TABLE 19 X-ray bombardment and these were designated K and L.He chose these mid-alphabe letters from his ame because he anticipated the discovery of other rays.and wished to leave alphabetical space on either side for future labeling of these rays. 1.44 THE PERIODIC TABLE An arrangement in tabular form of all the known elements in rows and columns in sequen of their mbers.The P iodic Table is ar expression oft tha ates many of the properties of the ization energies.,ele tron affinities,electronegativities,etc.)are a periodic f of their atomic numbers.By some estimates there may be as many as 700 different versions of the Periodic Table.A common display of this table.Fig.1.44a.consists of boxes placed in rows and columns.Each box shown in the table contains the sym- bol of the element,its atomic number,and a number at the bottom that is the aver- age atomic weight of the element determined from the natural abundance of its various isotopes s.There are seven rows of the elements corresp nding to the increas ing values of the principa m I to7.Ea rows bea with an element having one electron in the ns orbit tal and termi having the number of electrons corresponding to the completely filled K.M. and O shell containing 2,8,18,32,and 32 electrons,respectively.Row I consists of the elements H and He only;row 2 runs from Li to Ne;row 3 from Na to Ar,and so on.It is in the numbering of the columns,often called groups or families,where there is substantial disagreement among interested chemists and historians. The table shown in Fig.144g is a pular version (sometimes denoted as the American ABA scheme)of the Peri Table.In the ABA ve rsion the ele ents in d as belo ing ith Rom The elements are furthe erals r an A group or a B group.The A group elements are called representative or main group ele ments.The last column is sometimes designated as Group 0 or Group VIIIA.These are the rare gases;they are characterized by having completely filled outer shells: they occur in monoatomic form;and they are relatively chemically inert.The B group elements are the transition metal elements;these are the elements with ele rons in partially filled (n-1)d or(n-2)f orbitals.The 4th and 5th row transition metals alle tals nd the ele ments sho own in the 6th and 7th oat the om of Fig.1.44a are the sition me ough there is n of metd they are classified as such if they possess the following group characteristics:high electrical conductivity that decreases with increasing temperature;high thermal conductivity:high ductiliry (easily stretched,not brittle);and malleability (can be hammered and formed with- out breaking).Those elements in Fig.1.44a that are considered metals are shaded either lightly(A group)or more darkly (B group):those that are not shaded are non- metals:those having pr perties intermediate between metals and nonmetals are cross-hatc ed.Th of this last group are s called metalloids o these include .Thelements in the A sou have one to eisht ecro in hir oueosD boron,sil con,germar arsenic ony.and telX-ray bombardment and these were designated K and L. He chose these mid-alphabet letters from his name because he anticipated the discovery of other rays, and wished to leave alphabetical space on either side for future labeling of these rays. 1.44 THE PERIODIC TABLE An arrangement in tabular form of all the known elements in rows and columns in sequentially increasing order of their atomic numbers. The Periodic Table is an expression of the periodic law that states many of the properties of the elements (ion￾ization energies, electron affinities, electronegativities, etc.) are a periodic function of their atomic numbers. By some estimates there may be as many as 700 different versions of the Periodic Table. A common display of this table, Fig. 1.44a, consists of boxes placed in rows and columns. Each box shown in the table contains the sym￾bol of the element, its atomic number, and a number at the bottom that is the aver￾age atomic weight of the element determined from the natural abundance of its various isotopes. There are seven rows of the elements corresponding to the increas￾ing values of the principal quantum number n, from 1 to 7. Each of these rows begins with an element having one electron in the ns orbital and terminates with an element having the number of electrons corresponding to the completely filled K, L, M, N, and O shell containing 2, 8, 18, 32, and 32 electrons, respectively. Row 1 consists of the elements H and He only; row 2 runs from Li to Ne; row 3 from Na to Ar, and so on. It is in the numbering of the columns, often called groups or families, where there is substantial disagreement among interested chemists and historians. The table shown in Fig. 1.44a is a popular version (sometimes denoted as the American ABA scheme) of the Periodic Table. In the ABA version the elements in a column are classified as belonging to a group, numbered with Roman numerals I through VIII. The elements are further classified as belonging to either an A group or a B group. The A group elements are called representative or main group ele￾ments. The last column is sometimes designated as Group 0 or Group VIIIA. These are the rare gases; they are characterized by having completely filled outer shells; they occur in monoatomic form; and they are relatively chemically inert. The B group elements are the transition metal elements; these are the elements with elec￾trons in partially filled (n 1)d or (n 2)f orbitals. The 4th and 5th row transition metals are called outer transition metals, and the elements shown in the 6th and 7th row at the bottom of Fig. 1.44a are the inner transition metals. Although there is no precise chemical definition of metals, they are classified as such if they possess the following group characteristics: high electrical conductivity that decreases with increasing temperature; high thermal conductivity; high ductility (easily stretched, not brittle); and malleability (can be hammered and formed with￾out breaking). Those elements in Fig. 1.44a that are considered metals are shaded either lightly (A group) or more darkly (B group); those that are not shaded are non￾metals; those having properties intermediate between metals and nonmetals are cross-hatched. The members of this last group are sometimes called metalloids or semimetals; these include boron, silicon, germanium, arsenic antimony, and tel￾lurium. The elements in the A group have one to eight electrons in their outermost THE PERIODIC TABLE 19 c01.qxd 5/17/2005 5:12 PM Page 19