Chapter 19.2 Chapter 19.2 Chemical FormulasChemical Formulas

•Oxidation NumbersOxidation Numbers•Writing Chemical FormulasWriting Chemical Formulas

•Ionic CompoundsIonic Compounds•Writing Chemical FormulasWriting Chemical Formulas

•Naming Ionic & Covalent CompoundsNaming Ionic & Covalent Compounds•Empirical and molecular FormulasEmpirical and molecular Formulas

Oxidation NumbersOxidation Numbers

An oxidation number indicates how many An oxidation number indicates how many electrons will be lost, gained or shared electrons will be lost, gained or shared when bonding occurswhen bonding occurs

ALL COMPOUNDSALL COMPOUNDS have an electrical have an electrical charge ofcharge of ZERO ZERO When the oxidation numbers are added up for When the oxidation numbers are added up for

all of the atoms in a compound, the answer all of the atoms in a compound, the answer equals zeroequals zero

Oxidation Numbers & Oxidation Numbers & the Periodic Tablethe Periodic Table

You can use the periodic table to predict You can use the periodic table to predict the oxidation numbers for some of the the oxidation numbers for some of the groups.groups.

The transition metals are an exception, The transition metals are an exception, they have variable oxidation numbersthey have variable oxidation numbers

Periodic TablePeriodic Table

Writing Chemical Formulas for Ionic Writing Chemical Formulas for Ionic compoundscompounds

1)1) Write the symbol for the positive . Write the symbol for the positive . monatomic ion. (Groups 1, 2, & 13)monatomic ion. (Groups 1, 2, & 13)

2)2) Write the symbol for the negative Write the symbol for the negative monatomic ion. (Groups 15, 16, & 17)monatomic ion. (Groups 15, 16, & 17)

3)3) Add superscripts so that the sum of the Add superscripts so that the sum of the oxidation numbers equals zerooxidation numbers equals zero

Writing a Chemical FormulaWriting a Chemical Formula

CrissCross Applesauce CrissCross Applesauce is all you need to is all you need to knowknow

Ionic CompoundsIonic CompoundsPolyatomic IonsPolyatomic Ions

Most Ionic compounds are made up of Most Ionic compounds are made up of more than 2 types of atoms called more than 2 types of atoms called Polyatomic Ions. (see table on p. 337)Polyatomic Ions. (see table on p. 337)

Treat them just as you would when Treat them just as you would when working with monatomic ions, except you working with monatomic ions, except you need to put the polyatomic ion in brackets need to put the polyatomic ion in brackets and place the oxidation number as a and place the oxidation number as a superscript on the outside of the bracket.superscript on the outside of the bracket.

Naming monatomic Ionic Naming monatomic Ionic CompoundsCompounds

1)1) Write the root name of the second Write the root name of the second elementelement

2)2) Add “ide” to the root nameAdd “ide” to the root name

3)3) Write the name of the first element in the Write the name of the first element in the compoundcompound

Ex: Na + Cl = NaCl, Naming this chemical Ex: Na + Cl = NaCl, Naming this chemical formula would be , Sodium plus Chlorine formula would be , Sodium plus Chlorine equals Sodium chloride.equals Sodium chloride.

Naming Compounds with Naming Compounds with Polyatomic IonsPolyatomic Ions

1)1) Write the name of the positive ion firstWrite the name of the positive ion first

2)2) Write the name of the negative ion secondWrite the name of the negative ion second

You can use the periodic table or an ion chart to You can use the periodic table or an ion chart to get the names- There is one on get the names- There is one on p. 337p. 337 of your of your text booktext book..

Treat them just as you would the monatomic ions.Treat them just as you would the monatomic ions.

Empirical FormulaEmpirical Formula

The simplest whole number ratio by which The simplest whole number ratio by which the elements combine.the elements combine.

Ex: Hydrogen peroxide, each molecule Ex: Hydrogen peroxide, each molecule contains 2 hydrogen and two oxygen contains 2 hydrogen and two oxygen atoms, but the empirical formula is HOatoms, but the empirical formula is HO

Molecular FormulaMolecular Formula

A molecular formula contains the actual A molecular formula contains the actual number of atoms for each element in one number of atoms for each element in one molecule of the compoundmolecule of the compound

Ex: Hydrogen peroxide, each molecule Ex: Hydrogen peroxide, each molecule contains 2 hydrogen and two oxygen contains 2 hydrogen and two oxygen atoms, and the molecular formula is Hatoms, and the molecular formula is H22OO22