Writing Chemical Formulas

Chemical Formulas represent compounds.

Understanding Chemical Formulas Chemical formulas are composed of a positive half and a negative half. Ex. - Water is a compound you know to have a formula of H2O.

The Easiest Way to write chemical formulas! The easiest way to think of writing chemical formulas is to use the oxidation number (without the + or -) of one element as the subscript of the other element. (look at Periodic Table to get oxidation numbers) +2 -1 Ca Cl

Cross over the oxidation numbers without the charges!!! +2 -1 Ca Cl

Ca Cl 2 REMINDER: DO NOT write a subscript of 1. Reduce the subscripts if needed.

NAMING COMPOUNDS Your ability to name compounds and write formula’s hinges on your ability to recognize whether a compound is Ionic or Molecular.

BINARY IONIC COMPOUNDS Binary means 2 elements Ionic means a metal and a non-metal (or cation and anion) Writing Formulas • charges must balance so compound charge is neutral.

BINARY IONIC COMPOUNDS Writing Formulas from Names • 1st word = CATION • 2nd word = ANION name with ide ending.

BINARY IONIC COMPOUNDS NaBr MgF2 Sodium Bromide Magnesium Fluoride

BINARY IONIC COMPOUNDS Potassium Chloride Aluminum Oxide • notice ending of name is ide! K+Cl- -> KCl Al23+O32- -> Al2O3

Polyatomic Ions Definition •tightly bound groups of atoms that behave as a unit and carry a charge. Example SO32-, NO2-, ClO2-

TERNARY IONIC COMPOUNDS Ternary means 3 different elements Usually contain Poly-atomic Ions Ionic means cation and anion

TERNARY IONIC COMPOUNDS:Writing Formulas Ca2+CO32- -> CaCO3 Calcium Carbonate

TERNARY IONIC COMPOUNDS: Naming Calcium Nitrate Ca(NO3)2

Naming with Transition Metals First word = CATION Second word = ANION • You need to determine what charge is on the transition metal if more than one exists.

Naming Transition Metals Copper (I) Oxide Cu2O

Writing Formulas with Transition Metals FeCl3 FeCl2 Iron (III) Chloride Iron (II) Chloride

TYPES OF COMPOUNDS Molecular Compounds • composed of molecules in which elements share electrons. • usually composed of 2 nonmetals. • these elements are attached

MOLECULAR FORMULA Definition kinds of atoms present in a • shows the numbers and kinds of atoms present in a molecule of a compound. i. e. CO

TYPES OF COMPOUNDS Molecular Compounds con’t •Examples CS2 SiO2 BF3

BINARY MOLECULAR COMPOUNDS Binary means 2 elements Molecular means 2 non-metals NO ionic charges are present

Naming Binary Molecular Compounds Prefixes are used to show how many atoms are present in each molecule. mono, di, tri,tetra, penta, hexa, hepta, octa, nona, deca

Writing Binary Molecular Compounds Carbon Dioxide • Di means 2 oxygens!! CO2 •no mono prefix is used on first element

Naming Binary Molecular Compounds 2 ways it’s done! • (prefix + element name) i.e. N2O dinitrogen monoxide

Naming Binary Molecular Compounds • (prefix + element root + ide) i.e. PCl3 Phosphorous Trichloride All binary compounds end in ide!!!