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Chemistry : Elements & Radicals with Negative Valencies

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What is the Valency of an Element / Radical?

Valency is the number of hydrogen atoms that can combine with [or displace] one atom of the element [or radical] to form a compound. For example, one atom of hydrogen combines with one atom of chlorine to form hydrogen chloride [HCl]; so, the valency of chlorine [chloride] is one. Similarly, the valency of the nitrate radical [NO3] in the compound nitric acid [HNO3] is 1, and the valency of the sulfate radical in the compound sulfuric acid [H2SO4] is 2.

For elements that do not combine with hydrogen, the valency is the combining power of the element with another element whose valency is known. Valency may also be defined as the number of electrons that an atom donates or accepts to form the duplet state (i.e., 2 electrons in outermost shell) or octet state (i.e., 8 electrons in outermost shell).

The valency of an element [or radical] is always a whole number. Elements [or radicals] with valency one are monovalent, those with valency two are divalent, and those with valency three are trivalent. All nonmetals and nonmetallic radicals have negative valencies as shown in the table below.

Valency Element / Radical Symbol Ion
Monovalent [1] Chloride [Chlorine] Cl Cl1-
Hypochlorite ClO ClO1-
Chlorite ClO2 ClO21-
Chlorate ClO3 ClO31-
Perchlorate ClO4 ClO41-
Bromide [Bromine] Br Br1-
Hypobromite BrO BrO1-
Bromite BrO2 BrO21-
Bromate BrO3 BrO31-
Perbromate BrO4 BrO41-
Iodide [Iodine] I I1-
Hypoiodite IO IO1-
Iodite IO2 IO21-
Iodate IO3 IO31-
Periodate IO4 IO41-
Hydroxide OH OH1-
Nitrite NO2 NO21-
Nitrate NO3 NO31-
Bicarbonate [Hydrogen carbonate] HCO3 HCO31-
Bisulfite [Hydrogen sulfite] HSO3 HSO31-
Bisulfate [Hydrogen sulfate] HSO4 HSO41-
Dihydrogen phosphate H2PO4 H2PO41-
Cyanide CN CN1-
Cyanate CNO CNO1-
Thiocyanate SCN SCN1-
Permanganate MnO4 MnO41-
Acetate C2H3O2 C2H3O21-
Divalent [2] Oxide [Oxygen] O O2-
Peroxide O2 O22-
Carbonate CO3 CO32-
Sulfide S S2-
Sulfite SO3 SO32-
Sulfate SO4 SO42-
Thiosulfate S2O3 S2O32-
Biphosphate [Hydrogen phosphate] HPO4 HPO42-
Chromate CrO4 CrO42-
Dichromate Cr2O7 Cr2O72-
Oxalate C2O4 C2O42-
Trivalent [3] Phosphite PO3 PO33-
Phosphate PO4 PO43-

Note that a radical is a group of atoms of elements, e.g., sulfate radical [SO4]. An ion is any atom or group of atoms with a positive or negative charge due to loss or gain of electrons. Positively charged ions are called cations [e.g., Na1+], whereas negatively charged ions are called anions [e.g., Cl1-].


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