S.5 Chem Notes 2 Caltec S.5

CHEMISTRY NOTES Instructions. - READ AND WRITE THESE NOTES PLEASE - Equations and Diagrams will be elaborated during lessons. PERIODICITY The periodic table of elements is the chart in which the known chemical elements are listed inorder of increasing atomic number with chemically similar elements occupying the same vertical columns. The periodic table consists of two major divisions I) pe riods: this is the horizontal arrangement of elements. There are 7 periods. ii) groups: this is the vertical arrangement of elements There are 8 groups. Groups 1 to V11 are sub divided into A and B thus we can talk of I've and IV B. Group V111 has 3 col umns which include the groups containing iron nickel and cobalt respectively The Noble gases belong to group O The periodic table is as shown on the next page Leave one page for the periodic table It should be noted that there is no special resemblance between the chemistry of the subgroups A and B eg IV A elements are not related to IV B elements except perhaps their valencies The division into subgroups is merely a method used by Mendeleev in his original periodic table For simplicity we shall be mer ely referring to 1, 11,111 etc On analysis, it is observed that the elements within the same outer electronic configuration and similar chemical properties. However no element is exactly the same as another Elements within the same group show; Similar properties due to their similar outer electronic configuration A gradual change in properties down the group due to gradual change in electronegativity down the group However the first member in any group usually shows anomalous behavior due to high electronegativity small size and restriction to an octet of valence electrons. Elements usually exhibit valency corresponding to their group number …