Naming and Balancing Equations Review

Writing formulas for binary ionic compounds Composed of two elements - Monatomic cation(name of element followed by the word ion) -Monatomic anion(name of element ends with -ide) Ionic compounds are electrically neutral(net charge must be zero), therefore we must balance the charges when writing the formula Use the element symbols and remember the cation is always written first

Writing formulas example Calcium bromide Composed of calcium ions, Ca 2+ and bromide ions, Br – The ions must combine in a 1:2 ratio Each calcium ion with its 2+ charge must combine with(or be balanced by) two bromide ions, each with a 1- charge. Formula for calcium bromide is CaBr 2

Naming binary ionic compounds First write the name of the cation followed by the name of the anion(ending in –ide) When cations have more than one common charge the roman numeral must be included in brackets after the element name.

Naming example CoI 3 Cobalt and iodine Since there are 3 iodine in the compound, for the net charge to be zero, the charge on cobalt must be 3 + The name of the compound is cobalt(III) iodide

Ternary ionic compounds Contains atoms of three different elements Usually contains one or more polyatomic ions Procedure for writing the formula is same as binary compounds First write down the symbol and charge of the ions Then balance the charges An –ate or –ite ending on the compound indicates it contains a polyatomic anion Exceptions: hydroxide and cyanide

Example Calcium nitrate Composed of calcium ions, Ca 2+, and nitrate ions, NO 3 - To balance the charges two nitrate ions are needed to balance the 2+ charge on calcium Parentheses are used around the nitrate ion in the formula because two nitrate ions are need Formula is: Ca(NO 3 ) 2

Binary molecular compounds Composed of two nonmetallic elements. Ionic charges are not used in writing formulas Often combine in more than one way Prefixes are used to show how many atoms of each element are present in each molecule The second element’s name is written with an –ide ending Also note the vowel at the end of the prefix mono- is dropped when the name of the element begins with a vowel

Writing the formula example N 2 O Nitrogen and oxygen are present Two nitrogen and one oxygen Dinitrogen monoxide

Writing formulas for molecular compounds Very easy because the prefixes tell you the subscript of each element in formula Tertaiodine nonoxide Tetra=4 and nono=9 I 4 O 9

Writing formulas of Acids Acids are compounds that give off hydrogen ions when dissolved in water. General formula for acids are HX(X is a monatomic or polyatomic anion). Rules on naming 1) when anion ends in –ide, and the acid name begins with the prefix hydro- the acid name is the stem of the anion ending –ic followed by acid 2) when anion ends in –ite, the acid name is the stem of the anion ending in –ous followed by acid 3) when anion ends in –ate, the acid name is the stem of the anion ending in –ic followed by the word acid.

Example HClO Using rule 1- the ending of the polyatomic anion ends in –ide, therefore the acid is: hydrocyanic acid

Balancing Rules Determine the correct formula for all reactants and products and write them on the appropriate sides of reaction Count the number of atoms of each element in the reactants and products (polyatomic ion appearing on unchanged on both sides counts as one unit) Balance elements, other than hydrogen and oxygen, by using coefficients Balance hydrogen and oxygen last Check each atom and polyatomic ion to be sure equation is balanced Finally make sure the coefficients are at the lowest possible ratio

Example When hydrogen and oxygen react, the product is pure water. Write a balanced equation for reaction: First we can write a skeleton equation because the formulas for the reactants and products are known H 2(g) + O 2(g)  H 2 O (l) If we put a coefficient of 2 in front of H 2 O, the oxygen becomes balanced. H 2(g) + O 2(g) )  2H 2 O (l) Now there are twice as many hydrogen atoms in the product as there are in the reactants. To correct this, put a coefficient of 2 in front of H 2 and equation is now balanced. 2H 2(g) + O 2(g) )  2H 2 O (l) Check the coefficients. They must be in their lowest possible ratio 2(H2)s 1(O2), and 2(H2O)