Presentation on theme: "Writing Ionic Formulas. Ionic Compounds Things you should know: Ionic = metal-nonmetal combo of elements Metal: loses e- to become stable; positive."— Presentation transcript:
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