Introduction
There are just 26 alphabets in English language, but the number of words are innumerable. You have studied about the 115 known elements and how they are classified for systematic and comprehensive study. Thousands of compounds are born by various chemical reactions involving these elements.
Periodic Table and Valency of Elements
Group IA, IIA and IIIA consists of metals of normal elements. They have 1, 2, or 3 valence electrons which they can easily donate to acquire the configuration of nearest noble gas. They become positively charged i.e., cations.
Covalent Compounds and Periodic Table
Covalent compounds are formed by the sharing of electrons by atoms of non-metallic elements between groups IVA and VIIA. The elements of these groups react with one another by sharing election pairs. Thus, the valency of an element in a covalent molecule is equal to the number of electron pairs shared by an atom of the element.
Variable Valency
Normally metals donate electrons from their valence shell so as to form positively charged ions such that the charge on the ion is equal to its electropositive valency.
Formula of Ionic Compounds
Factoids
A chemical compound is always electrically neutral.The positive and negative valencies of the ions/radicals in a compound are equal and balanced.
Formula of Molecular Compounds
Covalent compounds are formed by the combination between two different non-metals. While writing the formula the less electronegative nonmetal element is written on the left hand side, whereas, the more electronegative non-metal is written on the right hand side.
Naming of Simple Compounds
Compounds formed by the combination of two different elements are called binary compounds. Example: CO, CCl4, H2S, NaCl, NH3, HBr. Binary compounds may be ionic or molecular.
Naming of Acids
The binary acids (acids containing hydrogen and one more element) are named by adding the prefix hydro- and suffix ic to the name of second element.
Chemical Equations
A chemical equation is a shorthand way of describing the events that occur in a chemical change or reaction.
The method of representing a chemical reaction with the help of symbols and formulae of the substances involved in it is known as a chemical equation.
Balancing of Chemical Equations
If the number of atoms of an element on both sides of a chemical reaction is equal, then the equation is said to be balanced.
How to make a Chemical Equation more Informative?
In three ways chemical equations can be made more informative.
1) By indicating 'physical states' of the reactants and products.
2) By indicating 'heat changes' taking place in the reaction.
3) By indicating the 'conditions' under which the reaction takes place.
Ionic Equations
Suppose we dissolve silver nitrate, an ionic solid in water, the ions in the crystal lattice are released and once in solution, move freely in hydrated form. The situation is represented by the equation:
Balancing of Ionic Equations
An ionic equation should be balanced with respect to the number of atoms or ions and also with respect to the number of charges on the ions i.e. to balance an ionic equation.
Chemical Reactions
Combination Reaction
The reactions in which two or more substances combine to produce a single substance are known as combination reactions or synthesis reactions. A reaction of this kind may be represented by the equation.
Reactivity Series
The arrangement of metals in a vertical column in the order of decreasing reactivity is called reactivity series of metals.
Summary
Symbol: It is a short hand notation of an element. E.g. sodium is denoted as Na.
