Names and Formulas for Ionic Compounds Chemistry Fall 2009 Section 8.3

Formulas for Ionic Compounds represented by a formula providing the simplest ratio of the ions involved called a formula unit represented by a formula providing the simplest ratio of the ions involved called a formula unit –KBr = potassium bromide; 1:1 ratio # e- gained by the nonmetallic atoms must equal the # e- lost by the metallic atoms; overall charge = 0 # e- gained by the nonmetallic atoms must equal the # e- lost by the metallic atoms; overall charge = 0 –MgCl 2 = (1) Mg 2+ ion & (2) Cl- ions

Determining Charge – monatomic ions Common Ions Based on Groups Group Atoms that commonly form ions Charge on ions 1A H, Li, Na, K, Rb, Cs 1+ 2A Be, Mg, Ca, Sr, Ba 2+ 3B Sc, Y, La 3+ 5A N, P, As 3- 6A O, S, Se, Te 2- 7A F, Cl, Br, I 1-

Oxidation Numbers and Writing Ionic Compound Formulas Oxidation number – the oxidation number or oxidation state of an element in an ionic compound equals the number of electrons transferred from an atom of the element to form the ion. The oxidation numbers are used to determine the formulas for the ionic compounds they form. The oxidation numbers are used to determine the formulas for the ionic compounds they form. Oppositely charged ions combine chemically in definite ratios to form a compound that has no charge. Oppositely charged ions combine chemically in definite ratios to form a compound that has no charge. If you add the oxidation number of each ion multiplied by the number of these ions in a formula unit, the total must be 0. If you add the oxidation number of each ion multiplied by the number of these ions in a formula unit, the total must be 0. –Example: K has a charge of +1 and O has a charge of -2. If the charges are not the same, subscripts must be determined to indicate the ratio of (+) to (-) ions. K 2 O –H/O Counting Atoms Worksheet

Charge of Transition Metals P. 222 in textbook: Common Ions of Transition Metals P. 222 in textbook: Common Ions of Transition Metals Charge of a monatomic ion = oxidation number Charge of a monatomic ion = oxidation number The number of e- transferred from an atom of the element to form the ion The number of e- transferred from an atom of the element to form the ion –Na+ and Cl- –Positively charged ion of a metal and negatively charged monatomic ion of a nonmetal –Oxidation state of Na is +1; Cl is 1- –Transition metals can form several different positive ions based on the variance in ionic charges of atoms in the groups

Now you try… Write the correct formula for the ionic compound composed of the following pairs of ions: Write the correct formula for the ionic compound composed of the following pairs of ions: a. potassium and iodide a. potassium and iodide b. magnesium and chloride b. magnesium and chloride c. aluminum and bromide c. aluminum and bromide d. cesium and nitride d. cesium and nitride e. barium and sulfide e. barium and sulfide H/O Writing Formulas Practice

Polyatomic Ions Polyatomic ions = ions made up of more than one atom Polyatomic ions = ions made up of more than one atom –Charge given applies to the entire group of atoms –Exists as a unit, never change subscripts of the atoms within the ion –If more than one is needed, place parentheses around the ion and write the appropriate subscript outside the parentheses Mg(ClO 3 ) 2

Polyatomic Ions you should memorize… ammonium (NH 4 ) sulfite (SO 3 2- ) nitrite (NO 2 - ) sulfate (SO 4 2- ) nitrate (NO 3 - ) phosphate (PO 4 3- ) hydroxide(OH - ) carbonate (CO 3 2- ) chlorite (ClO 2 - ) chlorate (ClO 3 - )

Now you try… Determine the correct formula for the ionic compound composed of the following pairs of ions: Determine the correct formula for the ionic compound composed of the following pairs of ions: a. sodium and nitrate a. sodium and nitrate b. calcium and chlorate b. calcium and chlorate c. aluminum and carbonate c. aluminum and carbonate d. potassium and chromate d. potassium and chromate e. magnesium and carbonate e. magnesium and carbonate

Naming Ions and Ionic Compounds Oxyanion = polyatomic ion composed of an element bonded to one or more oxygen atoms Oxyanion = polyatomic ion composed of an element bonded to one or more oxygen atoms 1. The ion with more oxygen atoms is named using the root of the nonmetal plus the suffix –ate. 2. The ion with fewer oxygen atoms is named using the root of the nonmetal plus the suffix –ite. Ex. NO 3 - NO 2 - SO 4 2- SO 3 2-Ex. NO 3 - NO 2 - SO 4 2- SO 3 2- nitrate nitrite sulfate sulfite nitrate nitrite sulfate sulfite

Oxyanions forming with halogens 1. The oxyanion with the greatest number of oxygen atoms is named using the prefix per-, the root of the nonmetal, and the suffix –ate 2. The oxyanion with one less oxygen atom is named with the root of the nonmetal and the suffix –ate 3. The oxyanion with two fewer oxygen atoms is named using the root of the nonmetal plus the suffix -ite

Oxyanions forming with halogens cont. 4. The oxyanion with three fewer oxygen atoms is named using the prefix hypo-, the root of the nonmetal, and the suffix –ite ClO 4 - ClO 3 - ClO 2 - ClO - ClO 4 - ClO 3 - ClO 2 - ClO - perchlorate chlorate chlorite hypochlorite perchlorate chlorate chlorite hypochlorite

Naming Ionic Compounds 1. Name the cation first and the anion second – CsBr 2. Monatomic cations use the element name – Cs is Cesium 3. Monatomic anions take their name from the root of the element name plus the suffix –ide – CsBr (bromide)

Naming Ionic Compounds Cont… 4. Group 1A and group 2A metals have only one oxidation number. Transition metals and metals on the right side of the periodic table often have more than one oxidation number – Fe 2 O 3 is named iron (III) oxide 5. If the compound contains a polyatomic ion, simply name the ion. NaOH is sodium hydroxide

Now you try… Name the following compounds: a. NaBr a. NaBr b. CaCl 2 b. CaCl 2 c. KOH c. KOH d. Cu(NO 3 ) 2 d. Cu(NO 3 ) 2 e. Ag 2 CrO 4 e. Ag 2 CrO 4 H/O Naming Ionic Compounds

Complete the following table… OxideChlorideSulfatePhosphate Potassium Barium Aluminum Ammonium