Page 17 - Theory and Problems of BEGINNING CHEMISTRY
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6                                    BASIC CONCEPTS                               [CHAP. 1


                             Table 1-3 Important Elements Whose Names and Symbols Should Be Known
                            1                                                           2
                             H                                                           He
                            3  4                                      5   6  7   8   9  10
                             Li  Be                                    B   C  N   O  F   Ne
                            11  12                                    13  14  15  16  17  18
                            Na Mg                                      Al  Si  P  S  Cl  Ar
                            19  20  21  22  23  24  25  26  27  28  29  30  31  32  33  34  35  36
                             K  Ca Sc  Ti  V  Cr Mn Fe Co   Ni  Cu Zn Ga Ge As    Se  Br  Kr
                            37  38                          46  47  48    50  51  52  53  54
                            Rb  Sr                          Pd Ag Cd      Sn Sb   Te  I  Xe
                            55  56            74            78  79  80    82  83        86
                            Cs Ba             W             Pt  Au Hg     Pb  Bi         Rn




                                          92
                                           U


                   The smallest particle of an element that retains the composition of the element is called an atom. Details of
               the nature of atoms are given in Chaps. 3 and 4. The symbol of an element is used to stand for one atom of the
               element as well as for the element itself.



               1.7. LAWS, HYPOTHESES, AND THEORIES
                   In chemistry, as in all sciences, it is necessary to express ideas in terms having very precise meanings. These
               meanings are often unlike the meanings of the same words in nonscientific usage. For example, the meaning of
               the word property as used in chemistry can be quite different from its meaning in ordinary conversation. Also, in
               chemical terminology, a concept may be represented by abbreviations, such as symbols or formulas, or by some
               mathematical expression. Together with precisely defined terms, such symbols and mathematical expressions
               constitute a language of chemistry. This language must be learned well. As an aid to recognition of special terms,
               when such terms are used for the first time in this book, they will be italicized.
                   A statement that generalizes a quantity of experimentally observable phenomena is called a scientific law.
               For example, if a person drops a pencil, it falls downward. This result is predicted by the law of gravity. A
               generalization that attempts to explain why certain experimental results occur is called a hypothesis. When a
               hypothesis is accepted as true by the scientific community, it is then called a theory. One of the most important
               scientific laws is the law of conservation of mass: During any process (chemical reaction, physical change, or


                                 Nonmetal
                                                               B
                                                               Al Si          Nonmetals
                                                                Ge As
                                                                   Sb Te
                                                                     Po At


                                                     Metals




                                                Fig. 1-1. Metals and nonmetals
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