Formulas and NamesSeptember14, 2011

CompoundsChemical compounds are two or more

elements chemically combined in fixed proportions

WHY do elements combine?The OCTET rule: atoms are most stable when their

outer-most energy levels are full of electronsAtoms want to be like the noble gases!

The first energy level can hold only TWO electronsThe second and beyond generally hold EIGHT electrons

How do elements combine?Molecular compounds

Share electrons

How do elements combine?Ionic Compounds

Some elements steal electrons from other elements!The result is IONS with opposite electric chargesOpposite charges attractCation = +Anion = -

How do elements combine?How many electrons is each element likely to gain or lose?

Molecular and Ionic Compounds

CharacteristicMolecular

CompoundsIonic Compounds

Unit Molecule Formula Unit

Type of elements NonmetalsMetals combined with

nonmetals

Phase of Matter Solid, liquid or gas Solids

Melting PointLow (usually below

300oC)High (usually above

300oC)

Representing CompoundsChemical Formulas = shows the kinds and

numbers of atoms in the smallest representative unit of the compoundEx) diatomic formulas

H2 F2 O2 Cl2

Representing compounds

NH3

Representing CompoundsFormula units – ionic compounds

Represent smallest whole number ratio of ions

16 Na+ and 16 Cl- Na16Cl16

Na1Cl1

NaCl

Naming CompoundsBinary Ionic Compounds (TWO ions)

‘cation name’ anion name –ide’

1A 2A 3A 4A 5A 6A 7A

Li+ Be2+ Al3+ N3- O2- F-

Na+ Mg2+ P3- S2- Cl-

K+ Ca2+ As3- Se2- Br-

Rb+ Sr2+ I-

Cs+ Ba2+

Ionic Charges of Common Elements

Naming CompoundsNaClBeOK2OAlF3

Calcium sulfideAluminum phosphideRubidium bromideMagnesium oxide

Naming CompoundsPolyatomic Ions

Sometimes atoms that are sharing electrons with each other will steal electrons from other atoms!!

Common Polyatomic IonsKnow these!!

Formula Name Charge

CO3 Carbonate -2

NO3 Nitrate -1

NH4 Ammonium +1

PO4 Phosphate -3

SO4 Sulfate -2

Writing FormulasIonic formula units must have a net ZERO chargePositive ion charges must balance negative ion

charges

Writing FormulasMagnesium fluoride

MgF2

Writing formulasPb2+ and Cl-

Al3+ and F-

K+ and Se2-

Sr2+ and P3-

Al3+ and S2-

K + and OH-

Cu2+ and NO3-

Al 3+ and CO32-

Today’s LabGOGGLES GOGGLES GOGGLESPipetteWell plate

Today’s LabEach reaction…CATION + ANION Ionic Compound

reactants yields products

Most ions are soluble, which means they will dissolve in water. However, today’s reactions result in insoluble products… we call these precipitates.