Ionic Compounds: Writing Formulas and Names Formula Units

Empirical Formulas Give the smallest whole-number ratio of elements in the compound. Ionic compounds have empirical formulas only.

Identify the empirical formulas H2O H2O2 CaF2 NaCl CH4 C2H6 NiO FeCl3 Empirical and possibly Molecular Molecular Empirical and Ionic Memory Jogger Empirical and Ionic Empirical and possibly Molecular Molecular Empirical and Ionic Empirical and Ionic

Formula Unit The simplest ratio of the ions in an ionic compound. KBr means potassium ions and bromide ions are in a 1-to-1 ratio and is the formula unit. For ionic compounds, the formula mass is based on the formula unit.

Binary Compounds Composed of two elements Positive monatomic metal ion Negative monatomic nonmetal ion Monoatomic ion is a one-atom ion. Note: A binary compound may contain more than 2 ions but only 2 kinds of ions like Al2O3.

Oxidation Number or State Na+1 Charge of a monatomic ion. Given by right superscript. Some elements form only 1 ion. Some elements can form more than 1 ion. Try to find patterns. Ca+2 O-2 Fe+2 and Fe+3

Oxidation State of Selected Elements Group 1 ions always +1 Group 2 ions always +2 MOST group 13 ions are +3 Groups 14, 15, 16, and 17 have multiple oxidation states, both positive and negative. (Start with the first ox #) Transition metals (Group B) can have more than 1 oxidation state but always positive.

Writing Formulas for Binary Cmpds The first rule in writing formulas for ionic compounds is POSITIVE ION FIRST But how do you get the subscripts? We will start by writing formulas from the ions.

Writing Formulas for Binary Cmpds Compounds are electrically neutral – no charge. Take the number of each kind of ion X the charge on the ion. Sum these terms. Should get 0. Positive and negative charges must balance out.

Equal but Opposite Charges Na+1 and Cl-1: NaCl +1 + (-1) = 0 Mg+2 and O-2: MgO +2 + (-2) = 0 Al+3 and P-3: AlP +3 + (-3) = 0 Rule: Just write the symbols, POSITIVE FIRST!

Try a few formulas: Li+1 and I-1 Ca+2 and O-2 Al+3 and N-3 K+1 and F-1 Ba+2 and S-2 LiI CaO AlN KF BaS

Criss-Cross Method When the charges don’t cancel out immediately: Mg+2 and Cl-1, CROSS and DROP! (Numbers only, forget signs!) Mg1Cl2 but if the subscript is 1, forget it! MgCl2 means 1 Mg+2 and 2 Cl-1

Check the Math MgCl2 means 1 Mg+2 and 2 Cl-1 (1 X +2) + (2 X -1) = 2 – 2 = 0 The charges add up to zero!

Try a few formulas: Ca+2 + Cl-1 Na+1 + O-2 Cs+1 + S-2 Al+3 + Cl-1 Al+3 + Se-2 Mg+2 + F-1 K+1 + N-3 CaCl2 Na2O Cs2S AlCl3 Al2Se3 MgF2 K3N

Of course, it gets more difficult Potassium (K) and Fluorine (F) Zinc (Zn) and Iodine (I) Sodium (Na) and Oxygen (O) Magnesium (Mg) and Oxygen (O) Aluminum (Al) and Oxygen (O) Calcium (Ca) and Bromine (Br) Cesium (Cs) and Iodine (I) Silver (Ag) and Sulfur (S) KF ZnI2 Na2O MgO Al2O3 CaBr2 CsI Ag2S

Naming Binary Ionic Compounds Always name the metal (the cation or positive ion) first and use its full name. Write the stem of the nonmetal (the anion or negative ion). Add the ending “ide” to the nonmetal.

Stems of nonmetals Nitr Ox Fluor Phosph Sulf Chlor Arsen Selen Brom Tellur Iod Hydr is the stem for H

The First Step in Naming Look up the positive metal in the periodic table in your reference tables. If the metal has only one oxidation state (possible charge), it’s easy. If the metal has more than one oxidation state, there’s an extra step.

Metals with one oxidation state Calcium Oxide CaO BaS AlN LiCl Al2Se3 Na2O K3N MgF2 Barium Sulfide Aluminum Nitride Lithium Chloride Aluminum Selenide Sodium Oxide Potassium Nitride Magnesium Fluoride

Metals with > 1 oxidation state. Use the formula to figure out which oxidation state the metal ion has. Ex: Fe can be Fe+2 or Fe+3 Name FeO and Fe2O3. These are two different compounds. You cannot name them iron oxide. Every formula goes with 1 name and vice-versa.

FeO and Fe2O3 FeO 1 O which is -2. The Fe must be +2. Name: Compounds are electrically neutral. Oxygen is -2. 1 O which is -2. FeO The Fe must be +2. Name: Iron (II) oxide The roman numeral II is the charge on the Fe.

FeO and Fe2O3 Fe2O3 Compounds are electrically neutral. Oxygen is -2. Each Fe is +3. Iron (III) oxide Each O is -2. Fe2O3 There are 3 O’s. 3 X (-2) = -6. Total negative charge. Total positive charge must be +6.

Name the following Hint: Positive Always First Titanium (III) chloride TiCl3 Mn2O4 Co2O3 PdBr2 AuCl3 MoN MnO TiO Manganese (IV) oxide Cobalt (III) oxide Palladium (II) bromide Gold (III) chloride Molybdenum (III) nitride Manganese (II) oxide Titanium (II) oxide

POLYATOMIC IONS SO42- CO32- PO43- OH- A group of covalently bonded atoms that carries a charge. See Table E. May be +’ve or –’ve. Polyatomic ions have “names.” Because they are charged, polyatomic ions can form ionic bonds with oppositely-charged ions. SO42- CO32- PO43- OH-

Ternary (or more) Compounds Contain 3 or more elements (uppercase letters) Usually have a polyatomic ion If the polyatomic is +’ ve, it’s bonded to a nonmetal If the polyatomic is –’ve, it’s bonded to a metal Once in a while, 2 polyatomics are bonded together.

Formulas with polyatomics What’s the formula for the compound formed from NH4+1 and Cl-1? The charges add up to zero, so just write the symbols, positive first! NH4Cl

Try a few more: Na+ and OH- NaOH K + and HCO3-1 Mg+2 and CO3-2 KHCO3 Li + and NO3- NH4 + and CN- Ca+2 and SO4-2 NaOH KHCO3 MgCO3 LiNO3 NH4CN CaSO4

These are more challenging: Mg3(PO4)2 Mg+2 and (PO4)-3 (NH4)+1 and S-2 Al+3 and (NO3)-1 Fe+2 and OH-1 Hg2+2 and SCN-1 Mg+2 and HCO3- Al+3 and C2O42- (NH4)2S Al(NO3)3 Fe(OH)2 Hg2(SCN)2 Mg(HCO3)2 Al2(C2O4)3

Some of the most challenging are Zn(NO3)2 Zinc + Nitrate ion Magnesium + Hydroxide ion Lithium + Carbonate ion Ammonium ion + Bromine Potassium + Sulfate ion Calcium + Phosphate ion Beryllium + Chlorate ion Ammonium ion + Sulfate ion Mg(OH)2 Li2CO3 NH4Br K2SO4 Ca3(PO4)2 Be(ClO3)2 (NH4)2SO4

Naming compounds with polyatomics Polyatomic ions have names, given in Table E. Naming is parallel to binary naming. Positive always first. If +’ve ion is a metal, check to see how many oxidation states it has. If > 1, name has a roman numeral. If –’ve is polyatomic, 2nd part of name is name of polyatomic. Don’t modify ending.

Name the following Sodium hydroxide NaOH KHCO3 LiNO3 CaSO4 Al(NO3)3 Fe(OH)2 CuSO4 CuSCN Potassium hydrogen carbonate Lithium nitrate Calcium sulfate Aluminum nitrate Iron (II) hydroxide Copper (II) sulfate Copper (I) thiocyanate

Summary for Ionic Compounds Name = metal + stem of nonmetal + ide. If the metal has more than 1 oxidation state, it has a roman numeral in the name. Formula: positive first, always. Compounds are electrically neutral. Use oxidation states you know, like O, to figure out the oxidation states that have more than 1 possibility.