Chemical formulas roman numerals

So far we have started with the chemical formula of a compound and decided on its systematic name. The reverse process is also important. For example, given the name calcium hydroxide, we can write the formula as Ca(OH)2 since we know that calcium forms only Ca2+ ions and that, since hydroxide is OH-, two of these anions will be required to give a neutral compound. Similarly, the name iron(II) oxide implies the formula FeO, since the Roman numeral II indicates the presence of Fe2+ and since the oxide ion is O2-. 

Group lA and group 2A metals have only one oxidation number. Transition metals and metals on the right side of the periodic table often have more than one oxidation number. To distinguish between multiple oxidation numbers of the same element, the name of the chemical formula must indicate the oxidation number of the cation. The oxidation number is written as a Roman numeral in parentheses after the name of the cation. For example, the compound formed from Fe + and has the formula FeO and is named iron(II) oxide. The compound formed from Fe + and has the formula Fe203 and is named iron(III) oxide. 

Before you can write a chemical formula from the name of a compound, you need to recognize what type of compound the name represents. For binary ionic compounds, the first part of the name is the name of a metallic cation. This may include a Roman numeral in parentheses. The anion name starts with the root of the name of a nonmetal and ends with -ide. 

Chemical formulas describe the simplest atom ratio (empirical formula), actual atom number (molecular formula), and atom arrangement (structural formula) of one unit of a compound. An ionic compound is named with cation first and anion second. For metals that can form more than one ion, the charge is shown with a Roman numeral. Oxoanions have suffixes, and sometimes prefixes, attached to the element root name to indicate the number of oxygen atoms. Names of hydrates give the number of associated water molecules with a numerical prefix. Acid names are based on anion names. Covalent compounds have the first word of the name for the element that is leftmost or lower down in the periodic table, and prefixes show the number of each atom. The molecular (or formula) mass of a compound is the sum of the atomic masses in the formula. Molecules are depicted by various types of formulas and models. 

To distinguish between multiple oxidation numbers of the same element, the name of the chemical formula must indicate the oxidation number of the cation. The oxidation number is written as a Roman numeral in parentheses after the name of the cation. 

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