Tiêu đề 1. The Language of Chyemistry.pdf ✅

Thus, the combining capacity of O is twice that of Cl, and that of N is thrice that of Cl. H is assigned a valency of 1. So the valencies of Cl, O and N are 1, 2 and 3 respectively. However, many atoms do not combine with H. Their valencies are calculated by the number of Cl atoms they combine with, since Cl and H have the same valency, i.e., 1.  The valency of an element is given by the number of H or Cl atoms that an atom o the element combines with. (You will learn in higher classes that the valency of an element can be expressed in many ways.) Elements with valencies 1, 2, 3, etc., are said to be monovalent, divalent (or bivalent), trivalent, and so on. The valencies of some common elements are indicated in Table Table: The valencies of some common elements Monovalent Divalent Trivalent Tetravalent Hydrogen Oxygen Nitrogen Carbon Chlorine Sulphur Aluminium Silicon Iodine Magnesium Sodium Calcium Potassium Zinc  Obtaining the formulae of compounds The formula of a binary compound, i.e., a compound formed by two elements only, is obtained by transposing their valencies. Suppose an element A has a valency y and element B has a valency x. Then the compound formed between A and B usually has the formula AxBy. The subscripts should be divided by a common factor, if any. A B 4 2 A B y x  A2B4  AB2  Ax By B 2 A 4 B 2 AB2 There are some exceptions like H2O2 (hydrogen peroxide) in which the numeral subscripts are not divided by the common factor. The formulae of some common compounds are given in table Table: Formulae of some common compounds Elements with valencies Formula Name of the compound 1 H 2 O H2O Water 1 H 1 Cl HCl Hydrogen chloride 1 Na 1 Cl NaCl Sodium chloride 2 Mg 1 Cl MgCl2 Magnesium chloride 2 Ca 1 Cl CaCl2 Calcium chloride 3 N 1 H NH3 Ammonia 2 Mg 2 O MgO Magnesium oxide 2 Ca 2 O CaO Calcium oxide 4 C 2 O CO2 Carbon dioxide