Simple ions – The ions which are formed from single atom carrying a positive or negative charge are called simple ions or mono-atomic ions.
Example – Na+, Cl–, O-2, Al+3, N-3(nitride), Mg+2, Ca+2, Cu+2, Fe+2etc.
Polyatomic ions -Polyatomic ions or compound ions are molecules formed from groups of atoms bonded together that carry a positive or negative charge.
Example – NH4+, CO3-2, OH–, SO4-2, NO3–, PO4-3, SO3-2 etc.
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Common Simple and Polyatomic Ions –
Carbon
CO3-2 carbonate
HCO3– hydrogen carbonate / (bicarbonate)
Nitrogen
NO3– nitrate
NO2– nitrite
N-3 nitride
NH4+ ammonium
Sulphur
SO42- sulphate
SO32- sulphite
S2O32- thiosulphate
HSO4– hydrogen sulphate / (bisulphate)
HSO3– hydrogen sulphite / (bisulphite)
S2- sulphide
Chlorine
ClO4– perchlorate
ClO3– chlorate
ClO2– chlorite
ClO– hypochlorite
Phosphorus
PO43- phosphate
HPO42- hydrogen phosphate
H2PO4– dihydrogen phosphate
Others
CN– cyanide
OH– hydroxide
Cl– chloride
F– fluoride
Br– bromide
I– iodide
H– hydride
H+ hydrogen
Na+ sodium
K+ potassium
Ag+ silver
Cu+ copper(I)
Mg+2 magnesium
Ca+2 calcium
O-2 oxide
Zn+2 zinc
Cu+2 copper(II)
Fe+2 iron (II)
Al+3 aluminium
Fe+3 iron (III)
Some elements show more than one valency. A roman numeral shows their valency in the bracket.
Don’t Miss –
Problems based on law of definite proportions or constant composition
How to write chemical formula of a simple Compound
How do you write Chemical Formula for an ionic Compound?
Common naming practices
If you can remember the formula of the ion whose name ends with ate, you can usually work out the formulas of the other family members as follows-
Stem name Meaning
-ate a common form, containing oxygen
Examples –
chlorate – ClO3–
nitrate – NO3–
sulphate – SO4-2
carbonate – CO3-2
Stem name Meaning
-ite one less oxygen than -ate form
Examples –
chlorite – ClO2–
sulphite – SO32-
nitrite – NO2–
Stem name Meaning
per-, -ate same charge, but contains one more oxygen
than -ate form
Examples –
perchlorate – ClO4–
perbromate – BrO4–
Stem name Meaning
hypo-, -ite same charge, but contains one less oxygen
than -ite form
Examples –
hypochlorite – ClO–
hypobromite – BrO–
Stem name Meaning
thio- replace an O with an S
Examples –
thiosulphate – S2O32-
thiosulphite – S2O22-
Some anions can capture hydrogen ions. For example, carbonate (CO3-2 ) can capture an H+ to produce hydrogen carbonate ( HCO3– often called bicarbonate). Each captured hydrogen neutralizes one minus charge on the anion.
Stem name Meaning
hydrogen or bi- captured H+ ions
Examples
hydrogen carbonate or bicarbonate – HCO3–
hydrogen sulphate or bisulphate – HSO4–
Stem name Meaning
dihydrogen captured 2H+ ions
Examples
dihydrogen phosphate – H2PO4–
Read also –
Law of Conservation of Mass
Problems based on Law of Conservation of Mass
Law of Definite Proportions / Constant Composition
- Radicals – An atom or group of atoms that contains one or more unpaired electrons (usually very reactive species). It can also be defined as a single atom or a group of atoms that behaves as a single unit and possess an electric charge.
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