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THE PERIODIC LAW Chapter 5 DMITRI MENDELEEV First person to create a periodic table • Periodic: repeating in pattern Mendeleev organized elements by increasing atomic mass Grouped elements with similar properties HENRY MOSELEY Arranged the periodic table by increasing atomic number Periodic Law: the physical & chemical properties of the elements are periodic functions of their atomic numbers • When elements are arranged by increasing atomic number, elements with similar properties appear at regular intervals MODERN PERIODIC TABLE An arrangement of the elements in order of their atomic numbers so the elements with similar properties fall in the same column or group PERIODS Horizontal rows 7 periods PERIODS Length of the period is determined by the number of electrons that can occupy the sublevels being filled by that period Period # Elements in Period Sublevels 1 2 1s 2 8 2s2p 3 8 3s3p 4 18 4s3d4p 5 18 5s4d5p 6 32 6s4f5d6p 7 32 7s5f6d7p GROUPS Vertical columns 18 groups REGIONS OF THE PERIODIC TABLE COLORS ON THE PERIODIC TABLE Indicate the state of matter at room temperature • • • • BLACK: solid RED: gas BLUE: liquid WHITE: synthetic/man-made BLOCKS S-BLOCK Groups 1 & 2 Reactive metals Notice: • Li= [He]2s1 • Na= [Ne]3s1 Group 1 (Alkali Metals) = ns1 Group 2 (Alkaline Earth Metals) = ns2 HYDROGEN & HELIUM Special cases H = 1s1 • Does not share properties with group 1 He = 1s2 • Part of group 18 because it’s first energy level is full with 2 e-s • Chemically stable like the noble gases P-BLOCK Groups 13-18 (except He) All contain 2 ns electrons Valence electrons = group # minus 10 • Ex. Group 17 minus 10 = 7 valence electrons Halogens (group 17): most reactive nonmetals because they are one electron short of a full outer shell Noble gases (group 18): unreactive because they have a full outer shell Metalloids: semiconducting elements MAIN-GROUP ELEMENTS s & p blocks D-BLOCK d-block groups don’t necessarily have identical outer electron configurations The sum of the outer s + d electrons = group # • Ex. Group 10 Ni = [Ar]3d84s2 Pd = [Kr]4d105s0 Pt = [Xe]4f145d96s1 Transition elements: d-block elements; metals with typical metallic properties F-BLOCK Lanthanides Actinides Involve filling 4f & 5f orbitals PERIODIC/GROUP TRENDS As you go across a period or down a group, trends can be observed in: • • • • • • Valence electrons Atomic radii Ionization energy Electron affinity Ionic radii Electronegativity VALENCE ELECTRONS Electrons available to be lost, gained, or shared in the formation of chemical compounds Main-group elements: valence electrons are in the outermost s & p sublevels • Correspond with the group number minus the transition elements • Ex. Group 1 = 1 valence electron Group 13 = 3 valence electrons VALENCE ELECTRONS Periodic Trend: as you go across a period, the # of valence electrons increases by 1 Group Trend: as you go down a group, the # of valence electrons stays the same (for main-group elements)