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Question
How to write chemical formulas?
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Solution
First, get a hold on notations of elements and their valencies. once you are done with the notation of elements and their valency, it would become easier. Chemical formulas are short-hand representations of compounds using chemical symbols and oxidation numbers. The simplest chemical formulas are for binary compounds - compounds made up of two elements.
1. Binary compounds have a positive half and a negative half.
2. The positive half is written first, the negative half second. Indicating numbers of atoms and molecules in formulas and equations 1. Subscripts are small numbers to the lower right of a symbol. They represent the number of atoms of that element in the compound.
2. Coefficients are large numbers to the left of formulas in chemical equations. They represent the ratio of molecules of each substance involved in a chemical reaction.
3. Subscripts and coefficients of 1 are omitted and are taken as default.
4. The subscripts indicate a "ratio" in which atoms combine to make compounds. For H2O - the ratio is 2 to 1 . . . 2 hydrogen atoms to 1 oxygen atom
Basically, we work with elements and their values. For, example consider the compound magnesium chlorides
Element Symbol Valency
Magnesium Mg +2
Chloride chloride Cl -1
Now, tourite the formula of compound, we start with elements and their valancies.
→ Write symbol with valency at the top
Mg+2 Cl−1
→ Cross multiply
Mg2+↔ Cl−1
→Mg,Cl2
→ As ⊥ is omitted, so formula is MgCl2
Some common ions and their valencies (charge) are listed below. Use them and practice more formulas.
Common CationsCharge Formula NameFormula Name1+HHydrogen ionNH+4Ammonium ionNa+Sodium ionK+Potassium ionCs+Cessium ionAg+Silver ion2+Mg2+MagnesiumCo2+CobaltCa2+Calcium ionCu2+Copper(II)or cupric ionSr2+Strontium ionFe2+Iron(II)or ferrous ionBa2−Barium ionMn2+Manganese(II)or manganous ionZn2+Zinc ionHg2+Mercury(I)or mercurous ionCd2+Cadmium ionHg2+Mercury(II) or mercuric ionNI2+Nickel(II) or nickelous ionPb2+Lead(II) or plumbous ionSn2+Tin(II) or stannous ion3+Al3+Aluminium ionCr3+fe3+Chromium(III)or chromic ion Iron(III)or ferric ion
Common~Anions\\
ChargeFormulaName1−H−Hydride ionF−Fluoride ionCl−Chloiride ionBr−Bromide ionI−Iodide ionCN−Cyanide ionOH−Hydroxide ion2−O2−Oxide ionO2−Peroxide ionS2−Sulfide ion3−N3−Nitride ion
- Common Polyatomic Ions - Click on the table for a more complete list
ionNameIonNameNH+4AmmoniumCO2−3CarbonateNO−2NitriteHCO−3Hydrogen carbonateNO−3NitrateClO−HypochloriteSO2−3SulfiteClO−2ChloriteSO2−4SulfateClO−3ChlorateHSO−4Hydrogen sulfate∗ClO−4PerchlorateOH−HydroxideC2H3O−2acetateCN−CyanideMnO−4PermanganatePO3−4PhosphateCr2O2−7DichromateHPO2−4Hydrogen phosphateCrO2−4ChromateH2PO−4dihydrogen phosphateO2−2peroxide
∗ Bisulfate and bicarbonate are widely used common names for hydrogen sulfate and hydrogen carbonate, respectively.
First, get a hold on notations of elements and their valencies. once you are done with the notation of elements and their valency, it would become easier. Chemical formulas are short-hand representations of compounds using chemical symbols and oxidation numbers.
The simplest chemical formulas are for binary compounds - compounds made up of two elements.
1. Binary compounds have a positive half and a negative half.
2. The positive half is written first, the negative half second.
Indicating numbers of atoms and molecules in formulas and equations
1. Subscripts are small numbers to the lower right of a symbol. They represent the number of atoms of that element in the compound. 2. Coefficients are large numbers to the left of formulas in chemical equations. They represent the ratio of molecules of each substance involved in a chemical reaction.
3. Subscripts and coefficients of 1 are omitted and are taken as default.
4. The subscripts indicate a "ratio" in which atoms combine to make compounds. For H2O - the ratio is 2 to 1 . . . 2 hydrogen atoms to 1 oxygen atom
Basically, we work with elements and their values. For, example consider the compound magnesium chlorides
Element Symbol Valency
Magnesium Mg +2
Chloride chloride Cl -1
Now, tourite the formula of compound, we start with elements and their valancies.
→ Write symbol with valency at the top
Mg+2 Cl−1
→ Cross multiply
Mg2+↔ Cl−1
→Mg,Cl2
→ As ⊥ is omitted, so formula is MgCl2
Some common ions and their valencies (charge) are listed below. Use them and practice more formulas.
Common CationsCharge Formula NameFormula Name1+HHydrogen ionNH+4Ammonium ionNa+Sodium ionK+Potassium ionCs+Cessium ionAg+Silver ion2+Mg2+MagnesiumCo2+CobaltCa2+Calcium ionCu2+Copper(II)or cupric ionSr2+Strontium ionFe2+Iron(II)or ferrous ionBa2−Barium ionMn2+Manganese(II)or manganous ionZn2+Zinc ionHg2+Mercury(I)or mercurous ionCd2+Cadmium ionHg2+Mercury(II) or mercuric ionNI2+Nickel(II) or nickelous ionPb2+Lead(II) or plumbous ionSn2+Tin(II) or stannous ion3+Al3+Aluminium ionCr3+fe3+Chromium(III)or chromic ion Iron(III)or ferric ion
Common~Anions\\
ChargeFormulaName1−H−Hydride ionF−Fluoride ionCl−Chloiride ionBr−Bromide ionI−Iodide ionCN−Cyanide ionOH−Hydroxide ion2−O2−Oxide ionO2−Peroxide ionS2−Sulfide ion3−N3−Nitride ion
- Common Polyatomic Ions - Click on the table for a more complete list
ionNameIonNameNH+4AmmoniumCO2−3CarbonateNO−2NitriteHCO−3Hydrogen carbonateNO−3NitrateClO−HypochloriteSO2−3SulfiteClO−2ChloriteSO2−4SulfateClO−3ChlorateHSO−4Hydrogen sulfate∗ClO−4PerchlorateOH−HydroxideC2H3O−2acetateCN−CyanideMnO−4PermanganatePO3−4PhosphateCr2O2−7DichromateHPO2−4Hydrogen phosphateCrO2−4ChromateH2PO−4dihydrogen phosphateO2−2peroxide
∗ Bisulfate and bicarbonate are widely used common names for hydrogen sulfate and hydrogen carbonate, respectively.
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