CBSE - IX - Chemistry - Atoms and Molecules
in the rules while writing the chemical formulae why we should symbol of the fist and then symbol.please explain in detial
1. write the correct symbols of the elements and radicals
2. Above each symbol, write the correct valence or oxidation numbers.
Ex. Al+3 O-2
3. To obtain the proper subscript, criss-cross the valence or oxidation
number,and drop the algebraic sign.
Ex. Al+3O-2 became Al2O3
Rule 2: When the subscript is number 1, subscript is not written.
Ex. Sodium Chloride- Na+1 Cl+1 --- NaCl
Rule 3: When the oxidation # of both elements are numerically equal but grater than 1, the subscript are not also written.
Ex. Calcium Oxide~ Ca+2O-2 ----- CaO
Rule 4: All radicals tke more than once( the subscript is 2 or more) must be
enclosed in Pahrentheses().
Ex. Ammonium Sulfate~~ NH4+1 SO4-2-----(NH4)2 SO4
RULE 4: All subscripts must be reduced to lowest term (except for molecular or
Ex. Tin (IV) Chloride ~ Sn+4Cl-1------ SnO2
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