Tells the relative number of atoms of each element in a compound Molecular covalent bonding Formula represents the number of atoms of each element in a single molecule Ionic ID: 509678
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Slide1
Chemical Formula
Tells the relative number of atoms of each element in a compoundMolecular: (covalent bonding)Formula represents the number of atoms of each element in a single moleculeIonic: (ionic bonding)Formula represents the simplest ratio of positive and negative ions in one formula unit
Episode
601Slide2
Ionic Bond
The attraction that binds opposite charged ions together.MetalsGive away electronsIons are positively chargedCationsNon-metalsTake electronsIons are negatively chargedAnions
Al
+3
Cl
-1
AlCl
3
Episode
601Slide3
Writing Ionic Formulas
Write the symbols for the elementsThe cation is written first (metal)The anion is written second (non-metal)Determine the charge on each ionSelect subscript that will make the total positive charge equal to the total negative
charge.
s
odium chloride
magnesium chloride
Na
Cl
Mg
Cl
+1
-
1
+2
-
1
NaCl
MgCl
2
Episode
601Slide4
Criss
-Cross Method for Formula WritingWrite the symbol of cation followed by symbol of anion along with their ionic charges.Use the absolute value of the charge of each ion as the subscript for the other.If the subscript is one, omit it.If the subscripts are the same, omit them.Subscripts must be simplified in an ionic formula.
b
arium iodide
c
alcium sulfide
Ba
+2
I
-1
Ba
1
I
2
BaI
2
C
a
+2
S
-2
Ca
2
S
2
CaS
Episode
601Slide5
Use the same steps to write formula
Treat the polyatomic ion as a single ionIf the subscript for the polyatomic is more than 1, put polyatomic ion in ( ) with subscript on the outside.Polyatomic Ions in formula writingsodium nitratecalcium nitrateNa+1NO3
-1
Na
1
(NO
3
)
2NaNO
3Ca
+2
NO
3
-1
C
a
1
Ca(NO
3
)
2
(NO
3
)1
Episode 601Slide6
Examples:
Calcium OxidePotassium chlorateAluminum sulfateCa+2O-2Ca2
O
2
CaO
ClO
4
-1
K
+1
(ClO
4
)
1
K
1
KClO
4
Al
+
3
SO
4
-2
Al
2
(SO
4
)
3
Al
2
(SO
4
)
3
Episode
601