writing ionic formulas
DESCRIPTION
Writing Ionic Formulas. Ionic Compounds. Things you should know: Ionic = metal-nonmetal combo of elements Metal: loses e- to become stable; positive ions Nonmetal: gains e- to become stable; negative ions The charge value (1, 2, or 3) depends on how many e- were lost or gained. - PowerPoint PPT PresentationTRANSCRIPT
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Writing Ionic Formulas
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Ionic Compounds Things you should know:
Ionic = metal-nonmetal combo of elements Metal: loses e- to become stable; positive
ions Nonmetal: gains e- to become stable;
negative ions The charge value (1, 2, or 3) depends on
how many e- were lost or gained. The # lost or gained was the # needed to
be “full”.
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Predicting Charges on IonsPredicting Charges on IonsKNOW THESE !!!!KNOW THESE !!!!
+1 +2 +3 -3 -2 -1 0
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Method One: electron dot diagrams
The # of dots shown = # of valence e-.
Column # = # of valence e-.e- are gained or lost in the #
needed for each atom/ion to be stable.
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e- dot diagrams for some common elements
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Use e- dot diagrams to show the transfer of e- to make the metal and nonmetal atoms stable.
e- dot diagram for Potassium (K) e- dot diagram for oxygen (O)
Transfer of e- to form potassium oxide
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Writing the Formula
If the ratio is 1:1, no subscript is needed. Ex: sodium chloride = NaCl
If the ratio is NOT 1:1 use a subscript for each element which has more than 1 ion involved in the transfer. Ex: potassium oxide = K2O
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Your Turn!
What is the formula of barium iodide? Show the e- dot diagram of each element. Show the transfer of e-. Write the formula based on the ratio of the
ions.
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Barium Iodide
e- dot diagram for Barium (Ba) e- dot diagram for iodine (I)
Transfer of e- to form barium iodide
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Formula
BaI2
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Method 2: using charges of the ions
Ion charge for Aluminum (Al) Ion charge for chlorine (Cl)
“Adding” the ions to get a neutral compound
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The formula
AlCI3
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Your Turn!
What is the formula of lithium sulfide? Determine the ion charge of each element. Determine the # of each ion needed to
form a neutral compound. Write the formula based on the ratio of the
ions.
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The Formula
Li2S
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Transition Metals
Transition metals = B column elements Charge can vary. It may be: +1, +2, +3,
or +4. A number in parentheses following the
name of the metal gives the ion charge. Ex: Iron (II) = Fe+2
Iron (III) = Fe+3
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Teacher Example
What is the formula of chromium (III) sulfide?
Ion charge for Chromium (Cr) Ion charge for sulfide
“Adding” the ions to get a neutral compound
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The formula
Cr2S3
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Your Turn!
What is the formula for silver (I) chloride?
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The formula
AgCI
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Polyatomic Ions Not all ionic compounds are composed
of metal and nonmetal elements. What?!?! All ionic compounds ARE composed of
positive and negative ions. Some ions are composed of 2 or more
elements. Poly = “many” Atomic = refers to
atoms
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Polyatomic Ions-continued= a group of atoms covalently
bonded together that has a net charge.
Examples:NH4
+ Ammonium C2H3O2
- AcetateCN- CyanideO2
2- PeroxideNO3
- Nitrate NO2
- NitriteSO4
-2 SulfateSO3
-2 Sulfite
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Together, the group has a charge. Like a molecule, the O and H atoms stay bonded together and act as one particle.
1–
HO
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OClO
1–
One chlorine atom and two oxygen atomscovalently bonded, together carrying a 1- charge
ClO2-
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Writing a formula that contains a polyatomic ion
Use the charge method. “Adding” the charges of the ions, the compound must be neutral.
Compound: Magnesium hydroxide
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Magnesium hydroxide
Ion charge for Magnesium (Mg) Ion charge for hydroxide (OH-)
“Adding” the ions to get a neutral compound
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The formula
Mg(OH)2
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Your Turn!
Write the formula for lithium phosphate.
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The formula
LiPO4
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Let’s Put It All TogetherTransitional metal and Polyatomic Ion What is the formula of chromium (III)
sulfate?
Ion charge for Chromium (Cr) Ion charge for sulfate
“Adding” the ions to get a neutral compound