Compounds and BondingCompounds and Bonding

GOAL: You will learn how GOAL: You will learn how elements combine to form elements combine to form

compoundscompounds

CompoundsCompounds A compound is formed when two or more A compound is formed when two or more

elements combine chemically. Elements join elements combine chemically. Elements join together in a way that makes them impossible together in a way that makes them impossible to separate by physical means. to separate by physical means.

Elements in a compound combine in a Elements in a compound combine in a predictable and definite ratio, based on the predictable and definite ratio, based on the combining property of the atoms involved.combining property of the atoms involved.

NaCl reflects a 1:1 ratioNaCl reflects a 1:1 ratio HH22O reflects a 2:1 ratioO reflects a 2:1 ratio COCO2 2 reflects a 1:2 ratioreflects a 1:2 ratio

Chemical FormulasChemical Formulas Chemical formulas are used to Chemical formulas are used to

represent compoundsrepresent compounds Chemical formulas indicate the kind Chemical formulas indicate the kind

of atoms in a compoundof atoms in a compound Subscripts are the small numbers in Subscripts are the small numbers in

a chemical formula which indicate a chemical formula which indicate the particular ratio of atoms in a the particular ratio of atoms in a compound compound

OxidationOxidation NumbersNumbers Is the name given to the combining Is the name given to the combining

ability of an atomability of an atomIndicates how many electrons an atom Indicates how many electrons an atom

gains, loses, or shares in forming a gains, loses, or shares in forming a compoundcompound

The sum of the oxidation numbers for The sum of the oxidation numbers for the atoms in a compound is zerothe atoms in a compound is zeroIn order for a compound to exist, it must In order for a compound to exist, it must

be electrically neutralbe electrically neutral

NaClNaCl Sodium loses one Sodium loses one

electron so it has electron so it has an oxidation an oxidation number of number of 1+1+Na Na 1+1+

Chlorine gains Chlorine gains one electron so it one electron so it has an oxidation has an oxidation number of number of 1-1-Cl Cl 1-1-

This works because 1(1+) + 1(1-) = 0

The sum of the oxidation numbers for the atoms in a compound is zero

HH22OO Hydrogen loses Hydrogen loses

one electron so it one electron so it has an oxidation has an oxidation number of number of 1+1+H H 1+1+

Oxygen gains rwo Oxygen gains rwo electrons so it has electrons so it has an oxidation an oxidation number of number of 2-2-O O 2-2-

This works because 2(1+) + 1(2-) = 0

The sum of the oxidation numbers for the atoms in a compound is

zero

Formula Figuring & WritingFormula Figuring & Writing The symbol of the metal or the The symbol of the metal or the

element with the positive element with the positive oxidation number is written firstoxidation number is written first

The ‘criss-cross’ method is a The ‘criss-cross’ method is a simple way of determining a simple way of determining a formulaformula The oxidation number of one The oxidation number of one

element becomes the subscript of element becomes the subscript of the otherthe other

‘‘Criss - Cross’ MethodCriss - Cross’ Method The formula for The formula for

the compound the compound composed of composed of potassium and potassium and sulfursulfur K K 1+1+ & S & S 2-2-

The formula for The formula for the compound the compound composed of composed of calcium and calcium and brominebromine Ca Ca 2+ 2+ & Br & Br 1-1-

This becomes K2S This becomes CaBr2

‘‘Criss-Cross’ Method Criss-Cross’ Method PracticePractice

Using Oxidation Using Oxidation Numbers, write Numbers, write formulas for the formulas for the compounds compounds formed from the formed from the following following elementselements

Sodium & BrominePotassium & IodineCalcium & FluorineHydrogen & SulfurMagnesium & FluorineLithium & Sulfur

Remember to check that the sum of the oxidation numbers is equal to zero!

NaBrNaBr

KIKI

CaFCaF22

HH22SS

MgFMgF22

LiLi22SS

Binary CompoundsBinary Compounds Binary Compounds are composed of two Binary Compounds are composed of two

elementselements Binary Compounds are named beginning Binary Compounds are named beginning

with the element with the positive oxidation with the element with the positive oxidation numbernumber

The name of the second element will end in The name of the second element will end in an an -ide-ideNaCl : Sodium ChlorideNaCl : Sodium ChlorideCaS : Calcium SulfideCaS : Calcium SulfideFeO : Iron OxideFeO : Iron Oxide

Binary Compounds Binary Compounds PracticePractice

Name each of the Name each of the followingfollowing

KIKI FeClFeCl33

LiLi22SS

Write formulas for Write formulas for the following:the following:

Calcium bromideCalcium bromide Potassium oxidePotassium oxide Aluminum chlorideAluminum chloride

Potassium Iodide

Iron Chloride

Lithium sulfide

CaBr2

K2O

AlCl3