8 FUNDAMENTAL PRINCIPLES 



separated into smaller fragments these are unlike and are definite in 

 number for every substance. These fragments are termed atoms. A 

 molecule of chalk is divisible into five atoms — one of carbon, one of 

 calcium, and three of oxygen. It has been found that an atom may be 

 further subdivided into much smaller particles, one or more of which lie 

 at the center and are termed protons, while the others, either associated 

 with the protons in a nucleus or distributed at distances about it, are 

 known as electrons. When, however, atoms are divided into these finer 

 particles, they are found to be all of the same nature, and so all matter in 

 this finely divided state becomes alike. Atoms of different kinds differ 

 only in the arrangement of these component particles with respect to 

 each other. 



12. Elements and Compounds. — This division of matter into mole- 

 cules, atoms, protons, and electrons belongs to physics. Chemistry, 

 strictly speaking, deals only with atoms classified according to their 

 kind and with molecules considered with respect to the kind and arrange- 

 ment of the atoms of which they are composed. Each kind of atom is 

 known as an element. Compounds are classified with respect to their 

 composition in terms of elements and also with respect to the manner in 

 which they react, or change, when brought in contact with other com- 

 pounds or with elements. Chemists now recognize about 90 different 

 elements, some of the most common of which are carbon, hydrogen, 

 oxygen, nitrogen, iron, calcium, phosphorus, sodium, and potassium. 

 To economize time and space in referring to these elements they are 

 designated by symbols, which may be the initial letter of the name of the 

 element, either in its English or in its Latin form, or two letters when 

 it is necessary to distinguish between elements having the same initial. 

 Thus, C represents carbon; Ca, calcium; H, hydrogen; N, nitrogen; and 

 Fe (from the Latin /errMm), iron. 



13. Acids, Bases, and Salts. — The elements are divided into two 

 categories. Metals, which number more than three-fourths of the total, 

 include gold (Au), silver (Ag), lead (Pb), copper (Cu), and iron (Fe), and 

 also calcium (Ca), magnesium (Mg), potassium (K), and sodium (Na). 

 The nonmetals include oxygen (0), nitrogen (N), carbon (C), sulphur (S), 

 silicon (Si), phosphorus (P), chlorine (CI), and iodine (I). Hydrogen 

 (H) is not a metal but in chemical combinations acts like one. Metals 

 combine with oxygen to form bases which, in solution in water, color 

 litmus more or less strongly blue — that is, they are alkaline. Nonmetals, 

 when combined with oxygen, yield acids which, in aqueous solutions, 

 are sour to the taste and color litmus red. All acids contain hydrogen. 

 A substance resulting from the union of a base and an acid is called a 

 salt. Examples are table salt, or sodium chloride (NaCl) ; hme, or calcium 

 carbonate (CaCOs); and blue vitriol, or copper sulphate (CUSO4). In 

 all chemical combinations the number of atoms of each element in a 



