 # Writing Ionic Formulas. Ionic Compounds  Things you should know: Ionic = metal-nonmetal combo of elements Metal: loses e- to become stable; positive.

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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. The # lost or gained was the # needed to be “full”.

Predicting Charges on Ions KNOW THESE !!!! +1 +2 +3 -3 -2 -1 0

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.

e- dot diagrams for some common elements

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

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 = K 2 O

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.

Barium Iodide e- dot diagram for Barium (Ba)e- dot diagram for iodine (I) Transfer of e- to form barium iodide

Formula  BaI 2

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

The formula  AlCI 3

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.

The Formula  Li 2 S

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

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

The formula  Cr 2 S 3

Your Turn!  What is the formula for silver (I) chloride?

The formula  AgCI

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

Polyatomic Ions-continued  = a group of atoms covalently bonded together that has a net charge.  Examples: NH 4 + Ammonium C 2 H 3 O 2 - Acetate CN - Cyanide O 2 2- Peroxide NO 3 - Nitrate NO 2 - Nitrite SO 4 -2 Sulfate SO 3 -2 Sulfite

Together, the group has a charge. Like a molecule, the O and H atoms stay bonded together and act as one particle. 1–1– H O

O Cl O 1–1– One chlorine atom and two oxygen atoms covalently bonded, together carrying a 1- charge ClO 2 -

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

Magnesium hydroxide Ion charge for Magnesium (Mg)Ion charge for hydroxide (OH-) “Adding” the ions to get a neutral compound

The formula  Mg(OH) 2

Your Turn!  Write the formula for lithium phosphate.

The formula  LiPO 4

Let’s Put It All Together Transitional 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

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