4.2 Names and Formulas of Compounds

Chemical Names All ionic compounds are composed of positive and negative ions The chemical name indicates which elements are present in the compound Each name has two parts: One for the positive ion One for the negative ion

Chemical Names To Name an Ionic Compound: Name the positive ion: - it’s the same as on the periodic table Name the negative ion -drop the end of the element name and add “ide”

Examples: NaCl KBr CaF2 4. MgO Sodium chloride Potassium bromide Calcium fluoride Magnesium oxide

Chemical Formulas Symbols represent the elements in the compound Subscript numbers following the symbol show how many of each element are present. Example: Sr3P2 - Contains 3 atoms Sr (strontium) and 2 atoms P (phosphorus)

Chemical Formulas The ion charge shows what ion each element forms to complete their valence shell of electrons Al has an ion charge of +3, therefore it loses 3 electrons Br has an ion charge of -1, therefore it gains one electron For Al and Br to form a compound Al needs to give away 3 electrons and Br needs to accept them. But wait!!! Br only needs to accept one, so how does this work??

Complete the “Chemical Formulas” worksheet to help you figure out how to determine the chemical formula for an ionic compound.

Chemical Formulas Each Br can accept only 1 electron, so 3 Br atoms are needed to combine with 1 Al The overall formula needs to show this  AlBr3

Chemical Formulas What would the Ionic Formula be for a compound made of Aluminum and Sulphur? Al has an ion charge of +3 S has an ion charge of -2

For all elements to end up with full valence shells, 2 atoms of Al and 3 of S are required. Formula = Al2S3

Shortcut to write the formula: Write the symbol and ion charge of the positive ion Write the symbol and ion charge of the negative ion Criss-cross the charges and write as subscripts Reduce numbers (if possible)

Examples: Aluminum sulphide Al+3 S-2 Al S Al2S3

Examples: Magnesium Oxide Mg+2 O-2 Mg O Mg2O2 REDUCE!! MgO

Assignment: Complete the practice problems on pages 86 and 87

Compounds Containing a Multivalent Metal Multivalent metals have more than one possible ion charge. The name must indicate which ion charge is used in the formation of the compound We use roman numerals to indicate ion charge: I = 1 VI = 6 II = 2 VII = 7 III = 3 VIII = 8 IV = 4 IX = 9 V = 5 X = 10

Compounds Containing a Multivalent Metal Examples: V4+ = Vanadium (IV) Ni3+ = Nickel (III) Writing formulas is identical to other ionic compounds, simply use the roman numeral to determine the ion charge of the cation!

Compounds Containing a Multivalent Metal Example: Manganese (IV) sulfide Mn4+ S2- Mn2S4 MnS2 ** Complete the practice problems on page 89**

Compounds Containing a Multivalent Metal Naming these types of compounds requires an extra step….you must UNCRISSCROSS!!

Compounds Containing a Multivalent Metal Example: Name PdS2 1. Look up the metal on the periodic table and confirm that it is multivalent. 2. Uncrisscross so that the subscripts become charges once again Pd1S2 Pd2+ S1-

Compounds Containing a Multivalent Metal Check the ion charge of the non-metal to make sure it’s correct. If not, multiply both charges to make it correct. Pd2+ S1- - wait!! Sulfur should have an ion charge of -2!! -to fix this, multiply both ion charges by 2 Pd4+ S2-

Compounds Containing a Multivalent Metal Name the metal, using roman numerals to indicate its ion charge Palladium (IV) Name the non-metal, swapping ending for –ide. Palladium (IV) Sulphide

Compounds Containing a Multivalent Metal Name these compounds: SnCl2 PbS2 Complete the practice problems on page 90!

Polyatomic Ions Some special molecules lose or gain electrons as a group These ionic molecules are called polyatomic ions

Polyatomic Ions You can recognize that a compound has a polyatomic ion in it because it will be made up of MORE THAN 2 TYPES OF ATOMS! Naming: Example: NaNO3 Name the cation Sodium 2. Name the polyatomic ion Nitrate Sodium Nitrate

Example: Calcium Bicarbonate Writing Formulas Write the symbol and ion charge for both parts of the name Criss Cross the charges - put brackets around the polyatomic ion if necessary 3. Reduce if possible Example: Calcium Bicarbonate Ca2+ HCO3- Ca HCO3 Ca(HCO3)2

Complete the practice problems on page 91 Complete Check Your Understanding page 95 #1-6