IONIC COMPOUNDS Formulas & Nomenclature

Formulas for Ionic Compounds Formula Unit – the simplest ratio of the ions represented in an ionic compound Because the total number of electrons gained by the nonmetallic atoms must equal the total number of electrons lost by the metallic atoms, the overall charge of the formula unit is zero.

Determining Charge Binary IONIC compounds are composed of positively charged monatomic ions of a metal and negatively charged monatomic ions of a non-metal. Monatomic ion – a one atom ion, such as Mg +2 or Br -1 Oxidation number – the charge of a monatomic ion

Practice Problems List the oxidation numbers for each of the following ions. A.Lithium ion G. Oxide ion B.Phosphide ion H. Calcium ion C.Bromide ion I. Beryllium ion D.Potassium ionJ. Francium ion E.Cesium ionK. Nitride ion F.Iodide ionL. Selenide ion

In the chemical formula for any ionic compound, the symbol of the cation is always written first, followed by the symbol of the anion. Subscripts, which are small numbers to the lower right of the symbol, are used to represent the number of ions of each element in an ionic compound. If no subscript is written, it is assumed to be one.

Example Problem 1: The ionic compound formed from potassium and oxygen is used as a dehydrating agent because it reacts readily with water. Determine the correct formula for the ionic compound formed from potassium and oxygen.

Potassium + Oxygen Step 1: Analyze the problem The first thing to do is write the symbol and oxidation number for each ion involved in the ionic compound K +1 O -2 “cross charges”

Potassium + Oxygen Step 2: Solve for the unknown A potassium ion loses one electron while an oxygen atom gains two electrons. If combined in a one- to-one ratio, the number of electrons lost by potassium will not balance the number of electrons gained by oxygen. To have the same number of electrons lost and gained, you must have two potassium ions for every oxide ion. The correct formula is: K 2 O

Potassium + Oxygen Step 3: Evaluate the answer Check to be sure the overall charge on the compound is ZERO K 2 OK +1 O -2 2(+1) + 1(-2) = 0

Practice Problems Write the correct formula for the ionic compound composed of the following pairs of ions: 1.Potassium & iodide 2.Magnesium & chloride 3.Aluminum & bromide 4.Cesium & nitride 5.Barium & sulfide

Practice Problems Write the correct formula for the ionic compound composed of the following pairs of ions: 1.Potassium & iodideKI 2.Magnesium & chlorideMgCl 2 3.Aluminum & bromideAlBr 3 4.Cesium & nitrideCs 3 N 5.Barium & sulfideBaS

Oxidation Numbers for Selected Transition Metals Silver+1 Zinc+2 Cadmium+2 All other transition metals have more than one oxidation number and have to be treated differently

Naming Binary Ionic Compounds A binary ionic compound is made up of a + metal (cation) and a – nonmetal (anion) The ending for the nonmetallic ion is –ide.

Steps for Naming Binary Ionic Compounds 1. Name the metal (cation) first and the nonmetal (anion) second. Remember, the cation is ALWAYS written first in the formula. 2. Monatomic cations use the metal name. 3. Monatomic anions take their name from the root of the element name plus the suffix -ide.

Name of Metal + Root of nonmetal + “-ide” ending (+ ion/cation) (- ion/anion) **no prefixes in ionic compound names**

Example: Write the name for BeCl 2 Step 1: Analyze the problem: Find the names of the elements associated with each symbol. Be – beryllium Cl - chlorine

Step 2: Solve for the unknown Name the metal. Name the root of the nonmetal and add the “-ide” ending. Beryllium chloride Step 3: Evaluate the answer Make sure the name makes sense and is correct for the formula.

Practice Problems Write the correct name for the following ionic compounds: NaI ZnO AlBr 3

Practice Problems Write the correct name for the following ionic compounds: NaIsodium iodide ZnOzinc oxide AlBr 3 aluminum bromide