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, Ca2+ 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 CaBr2

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

• CoI3

• 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, Ca2+, and nitrate

ions, NO3-

• 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(NO3)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

• N2O

• 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

• I4O9

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

ExampleWhen hydrogen and oxygen react, the product is purewater. Write a balanced equation for reaction:

• First we can write a skeleton equation because the formulas for the reactants and products are known

H2(g) + O2(g) H2 O(l)

• If we put a coefficient of 2 in front of H2O, the oxygen becomes balanced.

H2(g) + O2(g) ) 2H2O(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 H2 and equation is now balanced.

2H2(g) + O2(g) ) 2H2O(l)

• Check the coefficients. They must be in their lowest possible ratio 2(H2)s 1(O2), and 2(H2O)