Atoms are the small particles of which every element is made up of. The atom possesses the properties of its element.
Symbols are used to represent atoms of elements. If only one alphabet s present, then it is written in capital (K, N. O, F etc.). If two alphabets are present. then the first one is capital and the second one is a small letter (Fe, Ca, Na etc.)
It is the combining capacity of an element. It is equal to the number of hydrogen
atoms with which an atom of the element combines. Names, symbols. valency and atomic
masses of some common elements are listed in Table Below
Note: In the case of elements showing variable valencieS. the additional valencies are also given.
The higher valency of any metal is indicated by the letters - ic. Lower valenCy
by -ous. Thus
Cupric (Cu2+), Cuprous (Cu+), Mercuric (Hg2+), MercurouS (Hg+), Ferric (Fe3+),
Radicals: These are atoms or groups of atoms carrying the charges .
Positive radical: It is formed when a metal atom loses one or more electrons.
The name of the positive radical is same as that of the metal. Thus
NA -+ Na+ + e-
Ca -+ Ca2+ + 2e
Note: 1.The positive radicals go to the cathode during electrolysis. Hence they are called Cations.
2.These radicals are obtained from bases. Hence they are also called basic radicals.
Eg NaOH + Na+ +OH-
KOH -+ K+ +OH Here Na+ and K+ are cations / basic radals.
3.In writing the formula of a compound. positive radical is written first.
4 Example for non-metallic group of atoms acting as a cation : ammonium radical, NH+4.
Negative radical. It is formed when an atom or group of atoms gain one or more eiectrons.
CI + e- -+ CI-
Chlorine Chloride radical
:1.The negative radicals go to the anode during electrolysis. Hence they are called anions.
2.The radicals are obtained from acids. Hence they are called acid radicals.
Eg: HCI -+ H+ + CI-
H2SO4 -+ 2H+ + SO2-4
Apart from the above acid radical some of the following acid radicals are also met in the study of chemistry. A few of them are
Bromide : Br-, Iodide : 1, Nitrite : NO2-
Bicarbonate (hydrogen carbonate) : HCO3
Bisuiphafe(hydrogen sulphate) : HSO4
Sulphite : SO2-3