Properties, Writing Chemical Formulas & Naming Ionic Compounds

Ionic Compounds Compounds that are composed of cations and anions Binary Compound- compound composed of 2 elements Electrically Neutral Na 1+ +Cl1-  NaCl

Chemical Formula vs. Formula Unit Chemical Formula- shows different kinds of numbers of atoms in a small representative unit. Ex: H2O Formula Unit- lowest whole # ratio of ions in an ionic compound Ex: Na 1+ +Cl1-  NaCl; ratio 1:1 Ex: Mg 2+ +Cl1-  MgCl2 ; ratio 1:2

Properties Most are crystalline solids at room temperature Arranged in repeating 3 dimensional pattern Generally have high melting points Can conduct electric current when melted or dissolved in H2O salts

Writing Formulas for Ionic Compounds 1. Write the symbol of the cation first 2. Then write the symbol of the anion. 3. Add subscripts to balance charge Positive charge= negative charge

Examples 1. Potassium Chloride K 1+ Cl 1- 1 valence e’s 7 valence e’s lose 1 or lose 7 or gain 7 gain 1 Answer: KCl

#2 Calcium Bromide Ca Br 2 valence e’s 7 valence e’s lose 2 or lose 7 or gain 6 gain 1 Use Criss-cross method- numerical value of ion is crossed over and becomes subscript for other ion. Signs/Charges are dropped! Answer: CaBr2

#3 Iron (III) oxide Fe 3+ O2- Use the criss-cross method! Answer: Fe2O3

Now you try! Write the formulas for compounds formed from these pairs of ions 1. Ba 2+ , S2- 2. Ca 2+ , N3- 3. Li+ , O2- 4. Cu 2+ , I- 5. Sodium Iodide 6. Potassium Sulfide 7. Calcium Iodide 8. Aluminum Phosphide

Compounds with Polyatomic Ions Polyatomic ions- (not binary) have more than 2 ions, normally ends in –ate or –ite Writing Formulas with Polyatomic Ions Write symbol for cation followed by formula for polyatomic ion. 2. Balance the charges.

Example #1 Pearl + Oyster shell is made of calcium carbonate Ca 2+ CO32- Use Criss-cross method! Answer: CaCO3

Example #2 Calcium Nitrate Ca 2+ NO3- Use criss-cross method Answer: Ca(NO3)2

Example #3 Lead (II) sulfate is an important component in automobile batteries. Pb 2+ SO42- Use Criss-Cross method! Answer: PbSO4

Example #4 Ammonium Sulfate is used to make common fertilizers. NH4 1+ SO42- Use Criss-Cross Method! Answer: (NH4)2SO4

Naming Binary Ionic Compounds Place cation name first Next, name anion name [normally ends in –ide Naming Compounds with Polyatomic Ions Place cation name first. Look up on chart polyatomic anion name. *Exception to Rules: If cation is a transition metal, you must include its charge by writing it in Roman Numerals!

Examples Lithium iodide Li 1+ I 1- Answer: LiI Silver Carbonate Ag 1+ CO32- Answer: Ag2CO3

Examples Cu2O First show each ion and charge Cu 1+ O 2- Notice: when you criss-crossed those charges, what happened? Answer: Copper (I) oxide

Fe2O3 This means that Fe 3+ and O2- charge Answer: iron (III) oxide