Chemical Formulas
Chemistry
Dr. May
Valence Electrons
Sum of the outermost s an p electrons
• Na = 1
• N=5
• Ca = 2
• O=6
• Al = 3
• Cl = 7
• C=4
• Ne = 8
Oxidation Number
Number of electrons lost (+) or gained (–) during a
chemical reaction
• Na = +1
• N = +5 or –3
• Ca = +2
• O = –2
• Al = +3
• Cl = –1
• C = +4 or –4
• Ne = 0
NaCl Valence Electrons
• Na has one valence electron
1s22s22p63s1
• Cl has seven valence electrons
1s22s22p63s23p5
NaCl Ions
• Na transfers its electron to Cl to become the
Na+1 ion which has eight valence electrons
1s22s22p63s1  1s22s22p6
• Cl accepts the electron to become the Cl–1
ion which has eight valence electrons
1s22s22p63s23p5  1s22s22p63s23p6
Chemical Formulas - NaCl
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Sodium has an oxidation number of +1
Chlorine has an oxidation number of –1
One Na+1 combines with one Cl–1
One negative cancels one positive
NaCl is a neutral ionic compound
CaCl2 Valence Electrons
• Ca has two valence electron
1s22s22p63s23p64s2
• Cl has seven valence electrons
1s22s22p63s23p5
CaCl2 Ions
• Ca transfers its two electrons to two atoms of Cl to
become the Ca+2 ion which has eight valence
electrons
1s22s22p63s23p64s2   1s22s22p63s23p6
• Two Cl atoms accept the two electrons to become
two Cl–1 ions which have eight valence electrons
#1 Cl–1 1s22s22p63s23p5  1s22s22p63s23p6
#2 Cl–1 1s22s22p63s23p5  1s22s22p63s23p6
Chemical Formulas – CaCl2
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Calcium has an oxidation number of +2
Chloride has an oxidation number of –1
One Ca+2 combines with two Cl–1
Two negatives cancel two positives
CaCl2 is a neutral ionic compound
Na2O Valence Electrons
• Na has one valence electron
1s22s22p63s1
• O has six valence electrons
1s22s22p4
Na2O Ions
• Two atoms of Na transfer two electrons to one
atom of O to become two Na+1 ions each having
eight valence electrons
#1 Na+1 1s22s22p63s1  1s22s22p6
#2 Na+1 1s22s22p63s1  1s22s22p6
• O accepts the two electron to become the O–2 ion
which has eight valence electrons
1s22s22p4   1s22s22p6
Chemical Formulas – Na2O
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Sodium has an oxidation number of +1
Oxygen has an oxidation number of –2
Two Na+1 combine with one O–2
Two negatives cancel two positives
Na2O is a neutral ionic compound
Write Formulas
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Na +1 and Br –1
Na +1 and O –2
Ca +2 and Br –1
Ca +2 and O –2
Al +3 and Br –1
Al +3 and O –2
Fe +3 and Br –1
NaBr
Na2O
CaBr2
CaO
AlBr3
Al2O3
FeBr3
Six Polyatomic Ions
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OH –1 – Hydroxide
SO4 –2 – Sulfate
CO3 –2 – Carbonate
NO3 –1 – Nitrate
PO4 –3 – Phosphate
NH4+1 – Ammonium
Chemical Formulas – NaNO3
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Sodium has an oxidation number of +1
Nitrate has an oxidation number of –1
One Na+1 combines with one NO3–1
One negative cancels one positive
NaNO3 is a neutral ionic compound
Chemical Formulas – Na2SO4
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Sodium has an oxidation number of +1
Sulfate has an oxidation number of –2
Two Na+1 combine with one SO4–2
Two negatives cancel two positives
Na2SO4 is a neutral ionic compound
Chemical Formulas – Al(OH)3
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Aluminum has an oxidation number of +3
Hydroxide has an oxidation number of –1
One Al+3 combines with three OH–1
Three negatives cancel three positives
Al(OH)3 is a neutral ionic compound
Chemical Formulas – Ca3(PO4)2
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Calcium has an oxidation number of +2
Phosphate has an oxidation number of –3
Three Ca+2 combines with two PO4–3
Six negatives cancel six positives
Ca3(PO4)2 is a neutral ionic compound
Write Formulas
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Na +1 and NO3 –1
Na +1 and SO4 –2
Ca +2 and NO3 –1
Ca +2 and SO4 –2
Al +3 and NO3 –1
Al +3 and SO4 –2
Fe +3 and OH –1
NaNO3
Na2SO4
Ca(NO3)2
CaSO4
Al(NO3)3
Al2(SO4)3
Fe(OH)3
Write Formulas
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NH4 +1 and NO3 –1
NH4 +1 and SO4 –2
Ca +2 and CO3 –2
Ca +2 and PO4 –3
Al +3 and OH –1
Al +3 and PO4 –3
NH4+1 and OH –1
NH4NO3
(NH4)2SO4
CaCO3
Ca3(PO4)2
Al(OH)3
AlPO4
NH4OH
The End
• This presentation was created for the benefit
of our students by the Science Department
at Howard High School of Technology
• Please send suggestions and comments to
rmay@nccvt.k12.de.us