Chemical Formulas and Naming - Lighthouse Christian Academy

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2.6 Ionic Compounds: Chemical
Formulas and Naming
(7.3 pg 183-191)
• A chemical formula represents the relative
proportion of elements in a compound.
• There are 3 general types of ionic compounds that
we need to know how to name – they all follow the
same basic rule: the total ion charge for the
compound is equal to 0.
• The three types are:
– Binary ionic
compounds =
compounds that only
have two elemental
ions bonded together
(‘binary’ = 2; Table 1
p.183). E.g. (NaCl) or
(CaF2)
• The three types are:
– Multivalent ionic compounds = compounds containing
elements that can form more than one ion – the
element’s ions can have different charges
– E.g. (Iron can be Fe2+ or Fe3+).
• The three types are:
– Polyatomic ionic compounds = compounds that have
‘group ions’ as either the anion or the cation
– e.g. (SO42-). See Table 4 p.189 and your Data Pages.
• LET’S LOOK AT EACH TYPE OF IONIC COMPOUND
INDIVIDUALLY!
• WE’RE GOING TO NEED OUR TEXTBOOKS FOR THIS
– OPEN ‘EM UP TO CYU 7.3 PG.191
• GREAT INTRODUCTORY VIDEO:
• http://www.youtube.com/watch?v=URc75hoKGLY
• Binary ionic compounds; some examples include
Al2S3, CaF2, NaCl, etc.
– Naming binary ions is the easiest. First name the cation
(always listed first) then write the name of the anion
(always written second). Finally, change the end of the
anion to –ide.
– For example Al2S3 = Aluminum Sulfide
• Let’s try to name the other two examples listed
above!!!
• Binary ionic compounds; some examples include
Al2S3, CaF2, NaCl, etc.
– There are 2 ways to determine the formula of binary
ionic compounds (see pg 184-186).
– Here’s one way: look up the anion and the cation and
write them down with their charges. (for this example,
we’re determining the formula for Germanium Oxide)
– Ge4+ O2– Then (if necessary) multiply the ion charges on the
elements by whatever number it takes to get the charges
to balance. Here we’re using the ‘criss-cross’ or ‘drop &
swap’ method.
– Ge4+ O2- becomes Ge2O4 and since both #’s can be
divided by 2 we reduce it to GeO2
• Multivalent ionic compounds; some examples
include CuCl2, Cu2O, Fe2O3
– Naming multivalent compounds involves the same steps
as binary compounds. First name the cation, then write
down the charge on the cation with roman numerals in
brackets. Then name the anion but change the ending to
–ide. To figure out the charge on the cation you will need
to use the charge from the anion.
–
To name SnO2:
– 1st figure out the Charge on Sn
– Now name the cation and anion : Tin (IV) oxide
• Multivalent ionic compounds; some examples
include CuCl2, Cu2O, Fe2O3
– Drawing the formula for multivalent is the same as with
binaries. Start by writing the symbols with their charges.
Then use the criss-cross method.
• GREAT VIDEO: http://www.youtube.com/watch?v=p9iQ5Qn42DM
• Polyatomic Ionic compounds include either a cation
or anion that contains multiple elements
(‘polyatomic’ = multiple atoms). Some examples
include Al2(SO4)3, (NH4)2O
– Naming polyatomic ions is the same as naming binary
ionic compounds. First name the cation then name the
anion.
– For example Al2(SO4)3 is named aluminum sulfate. You
will need to refer to the list of polyatomic ions in your
Data Pages to determine the names/charges.
• Polyatomic Ionic compounds include either a cation
or anion that contains multiple elements
(‘polyatomic’ = multiple atoms). Some examples
include Al2(SO4)3, (NH4)2O
– To determine the formula from the name, write the
symbol for the cation first and then for the anion. Then
write their charges. If there will be more than 1
polyatomic ion, it has to be placed in brackets.
– Then use the criss-cross method.
– Remember to treat the polyatomic ion as a single unit.
• THAT’S ALL FOR IONIC COMPOUNDS.....FOR NOW

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