Transcript Naming and Balancing Equations

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 1charge.
• 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
•
•
•
•
N 2O
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
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
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)