Chemical Formulas and Names for Ionic Compounds

Terminology Review: A chemical formula uses chemical symbols to represent a particular compound. Compound – 2 or more different elements chemically bonded together in a fixed proportion

What are Ionic Compounds? - when one or more electrons are transferred from one atom to another, creating a neutral compound - pure substances usually consisting of one metal (donor or giver of electrons – therefore pos. charge) and one non-metal (receiver of electrons – therefore neg. charge)

Some Properties of Ionic Compounds: Crystal Lattice Solid high melting points ability to form crystals dissolve in water to form solutions that conduct electricity solid at room temperature Conductivity Soluble in Water

How are Ionic Compounds formed? Ionic bonds - attraction between oppositely charged ions How do ions form? - when one or more electrons move from a metal atom over to a non-metal atom

Rules to follow when writing Formulas and Naming Ionic Compounds:

(Element symbol and charge) a) & b) Ion formed from elements a) Write the symbol for the metal first, then the non-metal. b) Determine the ion charge each element would form. Write the charge to the upper right of the symbol. Elements to Combine a) b) Ion formed (Element symbol and charge) Magnesium Chlorine Mg2+ Cl-

REVIEW – What’s the Charge? Remember: Look at the valence electrons and ask yourself “What’s easiest?”. Let’s review………. Note the names of the non-metals when they turn into ions.

Predicting Ionic Charges Group 1: Lose 1 electron to form 1+ ions H+ Li+ Na+ K+

Predicting Ionic Charges Group 2: Loses 2 electrons to form 2+ ions Be2+ Mg2+ Ca2+ Sr2+ Ba2+

Predicting Ionic Charges Loses 3 electrons to form 3+ ions Group 13: B3+ Al3+ Ga3+

Predicting Ionic Charges Lose 4 electrons or gain 4 electrons? Group 14: Neither! Group 14 elements rarely form ions.

Predicting Ionic Charges Nitride Gains 3 electrons to form 3- ions Group 15: P3- Phosphide As3- Arsenide

Predicting Ionic Charges Oxide Gains 2 electrons to form 2- ions Group 16: S2- Sulfide Se2- Selenide

Predicting Ionic Charges F1- Fluoride Br1- Bromide Group 17: Gains 1 electron to form 1- ions Cl1- Chloride I1- Iodide

Predicting Ionic Charges Stable Noble gases do not form ions! Group 18:

Predicting Ionic Charges Many transition elements have more than one possible oxidation state. Groups 3 - 12: Iron(II) = Fe2+ Iron(III) = Fe3+

Predicting Ionic Charges Some transition elements have only one possible oxidation state. Groups 3 - 12: Zinc = Zn2+ Silver = Ag+

(Element symbol and charge) c) Determine the number of each ion needed to balance the charge. Elements to Combine a) b) Ion formed (Element symbol and charge) c) Balance the charges Magnesium Chlorine Cl- Mg2+ Mg2+ Cl- Cl- Criss-Cross Rule: Place the charge of one ion as the subscript of the other ion. Total: 2 + and 2 – Overall charge = 0

Write the chemical formula d) Write the chemical formula Rewrite the symbols together (no spaces) with the number of each needed as subscripts, reduce if possible Elements to Combine a) b) Ion formed (Element symbol and charge) c) Balance the charges d) Write the chemical formula Magnesium Chlorine Cl- Mg2+ Cl- Mg2+ MgCl2 Cl-

(Element symbol and charge) Write the chemical formula e) Write the name of the metal first, then the nonmetal by changing the ending to “ide”. Elements to Combine a) b) Ion formed (Element symbol and charge) c) Balance the charges d) Write the chemical formula e) Name the compound Magnesium Chlorine Cl- Mg2+ Cl- Mg2+ Magnesium Chloride MgCl2 Cl-

Polyatomic Ions A polyatomic ion is a group of atoms. has an overall ionic charge. Some examples of polyatomic ions are NH4+ ammonium OH− hydroxide NO3− nitrate NO2− nitrite CO32− carbonate PO43− phosphate HCO3− hydrogen carbonate (bicarbonate)

Naming Polyatomic Ions The names of common polyatomic anions end in ate. NO3− nitrate PO43− phosphate with one oxygen less end in ite. NO2− nitrite PO33− phosphite

Naming Compounds with Polyatomic Ions. The positive ion is named first, followed by the name of the polyatomic ion. NaNO3 sodium nitrate K2SO4 potassium sulfate (NH4)3PO3 ammonium phosphite

Writing Formulas with Polyatomic Ions. The Criss-Cross Rule still applies Na+ and NO3− -> NaNO3 with two or more polyatomic ions has the polyatomic ions in parentheses. Mg2+ and 2NO3− -> Mg(NO3)2 subscript 2 for charge balance