8 FUNDAMENTAL PRINCIPLES 



pound substance is termed a molecule. When molecules are 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 arrange- 

 ment of these component particles with respect to each other. 



13. 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 92 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 /errwm), iron. 



14. 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 hydrogen, 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) ; lime, or calc'um 

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

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



