Formulas and Names September14, 2011

Compounds Chemical 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 electrons Atoms want to be like the noble gases! The first energy level can hold only TWO electrons The 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 charges Opposite charges attract Cation = + Anion = -

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

Molecular and Ionic Compounds CharacteristicMolecular CompoundsIonic Compounds UnitMoleculeFormula Unit Type of elementsNonmetals Metals combined with nonmetals Phase of MatterSolid, liquid or gasSolids Melting PointLow (usually below 300 o C)High (usually above 300 o C)

Representing Compounds Chemical Formulas = shows the kinds and numbers of atoms in the smallest representative unit of the compound Ex) diatomic formulas H2 F2 O2 Cl2

Representing compounds NH 3

Representing Compounds Formula units – ionic compounds Represent smallest whole number ratio of ions 16 Na+ and 16 Cl- Na 16 Cl 16 Na 1 Cl 1 NaCl

Naming Compounds Binary Ionic Compounds (TWO ions) ‘cation name’ anion name –ide’ 1A2A3A4A5A6A7A Li + Be 2+ Al 3+ N 3- O 2- F-F- Na + Mg 2+ P 3- S 2- Cl - K+K+ Ca 2+ As 3- Se 2- Br - Rb + Sr 2+ I-I- Cs + Ba 2+ Ionic Charges of Common Elements

Naming Compounds NaCl BeO K2O AlF3 Calcium sulfide Aluminum phosphide Rubidium bromide Magnesium oxide

Naming Compounds Polyatomic Ions Sometimes atoms that are sharing electrons with each other will steal electrons from other atoms!!

Common Polyatomic Ions Know these!! FormulaNameCharge CO3Carbonate-2 NO3Nitrate NH4Ammonium+1 PO4Phosphate-3 SO4Sulfate-2

Writing Formulas Ionic formula units must have a net ZERO charge Positive ion charges must balance negative ion charges

Writing Formulas Magnesium fluoride MgF2

Writing formulas Pb 2+ and Cl - Al 3+ and F - K + and Se 2- Sr 2+ and P 3- Al3+ and S 2- K + and OH - Cu 2+ and NO 3 - Al 3+ and CO 3 2-

Today’s Lab GOGGLES GOGGLES GOGGLES Pipette Well plate

Today’s Lab Each 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.