Unit3 – Lecture 8

Recap – Bonding Occurs……to fill the outer level of electrons of

elementsyou can predict bonding by observing

trends on the periodic table: type of element: metals, non metals, etc

valence electrons: for lewis diagrams

oxidation #: criss-cross method

Counting AtomsChemical Formula -

shows how many of which atoms are in a molecule

Coefficient - placed in front of a molecule to show more than one molecule

Subscript - number placed below and behind a symbol to show how many of which atoms are present

3H2O

Counting AtomsDiatomic Molecule -

two atoms of the same nonmetal (usually in gas form) that have bonded together

Reactive nonmetals will bond with one another if no other substance is available for bonding

H2 N2

O2 F2

I2 Cl2

Br2

Polyatomic Ionsa group of atoms that

behave as one atomkeep together as a unitif more than one

polyatomic ion is present in a molecule, parentheses set it apartStill use a subscript to

show how manyHow many (OH)?

Ca(OH)2

NH4Cl

Common Polyatomic IonsSee your packet…

How Many?Making formulae –

the “Criss Cross” Method background:uses oxidation numbers to predict # of each

element in a compound when 2 elements bondOxidation # Review:

+ or – sign, indicates # of electrons that will be gained or lost

written like a charge in the upper right always included [given to you] if you have

polyatomic ions

Oxidation/Charge Numbers +1 +2 ----------------------------------------- +3 +/-4 -3 -2 -1 0

Oxidation #s – cont’dTransition metals have more than one

oxidation number!!!!Fe[III] = Fe+3 = Iron with +3 oxidation numberFe[II] = Fe+2 = Iron with +2 oxidation numberMn[II] = Mn+2 = Manganese with +2 oxidation

numberMn[III] = Mn+3 = Manganese with +3

oxidation number

Making Formulae – the “Criss-Cross” Methodcation first – write element & oxidation #anion next – write element & oxidation #without the + or – sign

write the oxidation # from one symbolon the other as a subscript

remember to add parentheses aroundpolyatomic ions

don’t write the #1, it is impliedreduce any evenly-divisible subscripts

ExamplesBond btw Aluminum and Oxygen

Bond btw Aluminum and Carbonate [CO3]-2

ExamplesBond btw Aluminum and OxygenAl +3 O -2

Al2O3

Bond btw Magnesium and Borate[BO3]-3

Mg +2 (BO3) -3

Al3(BO3)2

Practice Complete practice problems 1-9 in your packet.

Reverse Criss-Crossuse to find oxidation on atoms in a compound.

PCl3 P Cl3 So… P is 3, and Cl is 1

for transition metals – VERY useful

Ti Cl2 Ti Cl2 So… Ti is 2 and Cl is 1

Oxidation for Ti is +2

Binomial Nomenclaturea “two name” “naming” system

like Genus species from biology….Used to differentiate between elements and

compoundsFluorine (an element) vs

Fluoride (part of a compound)Never change the name of a Polyatomic Ion

Big difference between Sulfide, Sulfite, and Sulfate

Naming Ionic CompoundsList the positive ion (or metal) first

***Use Roman Numerals to show the Oxidation number of a transition metal

Name the negative ion (or nonmetal), changing the ending to –ide“Oxide”“Sulfide”“Phosphide”

Ex: FeO / Fe2O3

= Iron II Oxide / Iron III Oxide

Practice Complete practice – Naming Ionic Cmpds

page 14

Naming Polyatomic Compoundscmpd is polyatomic if there are more than 2

elements You will be given the names for common polyatomics.

Still only 2 words in the namefirst term = positive ion name second term = negative ion name

if second term is NOT a polyatomic, change ending to -ide

if the second term is a negative polyatomic, do NOT change the ending

Practicecomplete the practice problems 1-3.

Homeworkfinish any practice problems from lecture

complete Naming IONIC Compounds w/s [1-14] ONLY

HONORS ONLY:make 2 sets of polyatomic ion cards [for the ten

given]name formula [should still include charge…]name charge

Naming Covalent CompoundsPrefixes are used to show how many of which

atoms = number terms from Greek / Latin

Write the name of the cation [or most positive]only add a prefix for the first atom if

there is more than oneWrite the name of the anion [or most

negative]add a prefix to tell how many are presentchange the ending to -ide

Numbering Prefixes1 – Mono-2 – Di-3 – Tri-4 – Tetra-5 – Penta-

6 – Hexa-7 – Hepta-8 – Octa-9 – Nona-10 – Deka-

Practice What is the name for N2O4?

non-metal + non-metal…so covalentDinitrogen Tetraoxide

What is the name for Na2S?metal + non-metal = ionicSodium Sulfide

What is the name for CO2?non-metal + non-metal = covalentCarbon Dioxide

Practice – cont’dWhat is the name for (NH4)2O?

[hint: you need to know what (NH4) is…]Nitrogen Hydrogen OxideMononitrogen Tetrahydrogen OxideAmmonium OxideDiammonium OxideAmmonium Oxalate

CORRECT!!!!

Practice – cont’d