FIRST TWENTY ELEMENTS AND THEIR ATOMIC NUMBER, SYMBOL AND VALENCY ATOMIC NAME OF NUMBER(Z) ELEMENT SYMBOL VALENCE 1 Hydrogen H (-1), +1 2 Helium He 0 3 Lithium Li +1 4 Beryllium Be +2 5 Boron B -3, +3 6 Carbon C (+2), +4 7 Nitrogen N -3, -2, -1, (+1), +2, +3, +4, +5 8 Oxygen O -2 9 Fluorine F -1, (+1) 10 Neon Ne 0 11 Sodium Na +1 12 Magnesium Mg +2 13 Aluminum Al +3 14 Silicon Si -4, (+2), +4 15 Phosphorus P -3, +1, +3, +5 16 Sulfur S -2, +2, +4, +6 17 Chlorine Cl -1, +1, (+2), +3, (+4), +5, +7 18 Argon Ar 0 19 Potassium K +1 20 Calcium Ca +2
S.No 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
CHEMICAL COMPOUND FORMULAS NAME OF THE CHEMICAL COMPOUND FORMULA Acetic acid(Vinegar) CH3COOH Hydrochloric acid HCl Sulfuric acid H2SO4 Oxygen gas O2 Sodium bicarbonate(Baking soda) NaHCO3 Sodium chloride(Common salt) NaCl Ammonium hydroxide NH4OH Sodium hydroxide NaOH Magnesium hydroxide(milk of Mg(OH)2 magnesia) Copper sulphate CuSO4 Iron(II) sulphate FeSO4 Magnesium oxide MgO Calcium carbonate CaCO3 Iron oxide(rusted iron) Fe2O3 Carbondioxide CO2 Sodium bromide NaBr Zinc sulphide ZnS Sulphur dioxide SO2 Zinc chloride ZnCl2 Lead(II) nitrate Pb(NO 3 )2 Aluminum chloride AlCl3 Nitric acid HNO3 Sulphuric acid H2SO4 Carbonic acid H2CO3 Water H2O
SOME OF BASIC RADICALS AND THEIR POSITIVE VALENCE Plus One Valence Ammonium NH4+
Plus Two Valence Calcium Ca2+
Plus Three Valence Aluminum Al3+
Cuprous/Copper(I) Potassium
Cu+ K+
Zinc Cupric/Copper(II)
Zn2+ Cu2+
Ferric/Iron(III)
Silver
Ag+
Ferrous/Iron(II)
Fe2+
Antimony
Sb3+
Sodium
Na+
Lead(II)/Plumbous Magnesium Manganese
Pb2+ Mg2+ Mn2+
Arsenic Chromium
As3+ Cr3+
Plus Four Valence Lead(Plumbic) Pb4+
Fe3+ Carbon
C4+
Silicon
Si4+
SOME ACIDIC RADICALS AND THEIR VALENCY Minus One Valence Acetate(C2 CH3COOH3O 2) Bicarbonate HCO3Bromide BrChloride Fluoride
ClF-
Hydroxide Iodide
OHI-
Nitrate Permanganate
NO3MnO4-
Minus Two Valence Carbonate CO32Oxide Sulfide/Sulphide
O2S2-
Sulfite /Sulphite Sulfate
SO32SO42-
Minus Three Valence Phosphate PO43-
Minus Four Valence Silicate SiO4 Ferrocyanide
Fe(CN) 6
BOHR’S MODEL OF ATOM
How are Electrons Distributed in Different Orbits (Shells)? (i) The maximum number of electrons present in a shell is given by the formula 2n2, where ‘n’ is the orbit number or energy level index, 1,2,3,…. Hence the maximum number of electrons in different shells are as follows: first orbit or K-shell will be = 2 X 12 = 2, second orbit or L-shell will be = 2 X 22= 8, third orbit or M-shell will be = 2 X 32 = 18, fourth orbit or N-shell will be = 2 X 42= 32, and so on. (ii) The maximum number of electrons that can be accommodated in the outermost orbit is 8. (ii) Electrons are not accommodated in a given shell, unless the inner shells are filled. That is, the shells are filled in a step-wise manner. SUBATOMIC PARTICLE
Electron Proton Neutron
SYMBOL/REPRESENTATION
e−, β− p , p, N+ n, n0, N0 +
ATOMIC STRUCTURE OF THE FIRST EIGHTEEN ELEMENTS IS SHOWN SCHEMATICALLY