Chemistry (NTSE/Olympiad)  

3. Atoms & Molecules


The combining capacity of an element is known as its valency.
Formulae and valencies of common ions
Electropositive Ions
Monovalent Bivalent
Name Formula Name Formula
Potassium K+ Barium Ba2+
Sodium Na+ Calcium Ca2+
Copper [I] Cu+ Magnesium Mg2+
Manganese [II] Mn2+
Zinc Zn2+
Silver Ag+ Iron [II] Fe2+
Ammonium NH4+
Hydrogen H+ Nickel Ni2+
Cobalt Co2+
Tin [II] Sn2+
Cadmium Cd2+
Lead [II] Pb2+
Copper [II] Cu2+
Trivalent Tetravalent
Name Formula Name Formula
Aluminium Al3+ Manganese [II] Mn4+
Chromium Cr3+ Tin [IV] Sn4+
Iron [III] Fe3+ Lead [IV] Pb4+
Gold Au3+ Platinum Pt4+

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