Laws of chemical combination :

 When two or more substances react chemically a compound is formed. The force which holds together the ions, atoms and molecules in a chemical substance is called as chemical bond. It is the same force which makes substances combine with each other in many different ways to give newer products and this is called chemical combination. The combining tendency of atoms to form chemical bonds can be explained in term of the electronic theory of valency, which states that: the tendency of an atom to take part in chemical combination is determined by the number of valence electrons, The atoms acquire the stable noble gas configuration of having eight electrons in the outermost shell by mutual sharing or by transfer of one or more electrons, The valency of an element is either equal to the number of valence electrons. There are few laws which direct the formation of chemical compounds. There are many aspects of a chemical reaction like the rate of reaction, energy absorbed or evolved, mechanism of a reaction that can be evaluated only with weight and volume relationships. Substances react by following certain laws called the laws of chemical combination. They are as follows: Law of Conservation of Mass states that matter can neither be created nor destroyed. In a chemical reaction the total mass of the reactants is equal to the total mass of the products. Law of Definite Proportions states that a chemical compound contains the same elements in a fixed ratio by weight. Law of Multiple proportions states that when two elements combine to form two or more compounds, the different weights of one of the elements combining with the constant weight of the other bear a simple numerical ratio to one another. Law of Reciprocal Proportions states that the ratio between the weights of two elements which combine with the fixed weight of the third element will be same or simple multiples of the ratio in which the elements combine together. Law of Combining volumes states that the volumes of reacting gases and product gases if any beat a simple numerical ratio to one another.