Step #4 - since a formula must have zero total charge, you write the formula Fe 2S 3. Step #3 - Sulfide (the anion) means S 2¯. remember, that comes from the Roman numeral. Step #2 - the charge on the cation is a positive three. Step #1 - the symbol of the cation is Fe. Step #4 - since a formula must have zero total charge, you write the formula Cu 2O.Įxample #3 - Write the formula for: iron(III) sulfide Step #3 - the anion symbol and charge comes from the second name. Step #2 - the Roman numeral WILL tell you the charge on the cation. Step #1 - the first word tells you the symbol of the cation. Chloride is the name and Cl¯ is the face.Įxample #2 - Write the formula for: copper(I) oxide The ChemTeam is often asked by students, "But how do you know that chloride means Cl¯?" That type of question is usually answered with a question, as in "How do you know the name and face of your best friend?" That's right, you've spent time in their company, to the point where you have memorized the connection between name and face. On writing the formula from the ions, you may want to review Charge-Crossing.html or Least-Common-Multiple.html for more information. Step #4 - remembering the rule that a formula must have zero total charge, you write the formula CuCl 2. This suggestion has not been followed, but the Stock system remains in use world-wide.Įxample #1 - Write the formula for: copper(II) chloride In 1934, Stock approved of the Roman numerals, but felt it better to keep the hyphen and drop the parenthesis. For example, FeCl 2,which would have been named iron(2)-chloride according to Stock's original idea, became iron(II) chloride in the revised proposal. In 1924, a German commission recommended Stock's system be adopted with some changes. In his own words, he considered the system to be "simple, clear, immediately intelligible, capable of the most general application." It was designed by Alfred Stock (1876-1946), a German chemist and first published in 1919. The type of naming you will learn about is called the Stock system or Stock's system. The ChemTeam holds their students responsible for: Cu, Fe, Hg, Pb, Sn, Mn, Co, Au, and Cr. Your teacher will hold you responsible for the cations you must learn. The anions involved have only one charge. The cations involved in this lesson have AT LEAST TWO charges. The four formulas above are all examples of this type. This lesson shows you how to write the formula of a binary compound from the word name when a cation of variable charge is involved. There can also be several of each element such as Fe 2O 3 or SnBr 4. There can be one of each element such as in CuCl or FeO. to balance it will need, one Ca 2+ ion and two OH - ions,ĭeduce the formula for sodium carbonate.ChemTeam: Nomenclature-Binary Compounds:Stockīinary Compounds of Cations with Variable ChargesĪ binary compound is one made of two different elements.this is two positive charges and one negative charge.ExampleĬalcium hydroxide contains Ca 2+ and OH - ions: If more than one polyatomic ion is needed, its formula is written inside brackets. The formulae of compounds containing polyatomic ions are worked out in a similar way to single atom ions. The table shows the names and formulae of some of these ions. Polyatomic ions are formed from groups of atoms. The table shows the formulae of some common transition metal ions. The number in the name of the compound shows the charge of the metal ions in that compound.įor example, copper(II) sulfate contains Cu 2+ ions. Transition metals (in the central block between groups 2 and 3) can have ions with different charges. Elements in the same group form ions with the same charge. The charge of many ions can be worked out using patterns in the periodic table.
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