6Brown T L, Lemay H E, Bursten B E, et al. Chemistry:The Central Science [ M ]. 8 th edition. Upper Saddle River, New Jersey, USA: Pearson Prentice Hall, 1999 : 3-4.
7Myers R. The basics of chemistry [ M ]. Westport, Connecticut, USA : Greenwood Publishing Group,2003:13-14.
8Pauling L. General Chemistry [ M ]. Mineola, New York, USA : Dover Publications Inc, 1947 : 1-5.
9Chang R. Chemistry[ M ]. 6th edition. New York ,USA :McGraw Hill, 1998:3-6.
10Hill J W, Petrucci R H, McCreary T W, et al. General Chemistry [ M ]. 4th edition. Upper Saddle River, New Jersey, USA: Pearson Prentice Hall,2005:37.