Chapter 4 “Chemical Names and Formulas” Modified and adapted from Pre-AP Chemistry Charles Page High School Stephen L. Cotton H2OH2O

Section 4.3 Naming and Writing Formulas for Molecular Compounds l OBJECTIVES: –Interpret the prefixes in the names of molecular compounds in terms of their chemical formulas.

Section 4.3 Naming and Writing Formulas for Molecular Compounds l OBJECTIVES: –Apply the rules for naming and writing formulas for binary molecular compounds.

Molecular Compounds  Compounds where - both elements have neg. charges - both elements are from right side - both element are non-metals - electrons are shared, not transferred - they generally have low MP & so can be a S/L/G

Molecular compounds are… l made of just nonmetals l smallest piece is a molecule l can’t be held together by opposite charge attraction l can’t use charges to figure out how many of each atom (there are no charges present)

Molecular compounds are easier! l Ionic compounds use charges to determine how many of each. –You have to figure out charges. –May need to criss-cross numbers. l Molecular compounds: the name tells you the number of atoms. –Uses prefixes to tell you the exact number of each element present!

Molecular Compounds l Binary molecule –2 atoms w/ covalent bond l Rules for naming binary molecules 1st element has normal name 2nd element has ending changed to -ide Use prefixes to say how many of each element Do not use a prefix with the first element if there is only one. –(ex. CO - carbon monoxide)

Molecular Naming Prefixes 1mono 6hexa 2di 7hepta 3tri 8octa 4tetra 9 nona 5penta 10 deca

Prefixes l To write the name, write two words: Prefix & name Prefix & name-ide

Prefixes l To write the name, write two words: l l One exception is we don’t write mono if there is only one of the first element. PrefixnamePrefixname-ide

Prefixes l To write the name, write two words: l l One exception is we don’t write mono if there is only one of the first element. l Normally, we do not have double vowels when writing names (oa oo) PrefixnamePrefixname-ide

Name the compounds Formula Name CO 2 CO PCl 3 N2P4N2P4 SO 4 N2O5N2O5 S 4 Cl 9

Name the compounds Formula Name CO 2 Carbon Dioxide COCarbon Monoxide PCl 3 Phosphorus Trichloride N2P4N2P4 Dinitrogen Tetraphosphide SO 4 Sulfur Tetroxide N2O5N2O5 Dinitrogen Pentoxide S 4 Cl 9 Tetrasulfur Nonachloride

Write the formulas 1. dinitrogen monoxide 2. phosphourus trichloride 3. sulfur hexafluroride 4. carbon disulfide 5. carbon tetrabromide 6. dinitrogen tetrahydride 7. boron trichloride 8. diphosphourus trioxide 9. hexaselenium monochloride

Write the formulas 1. dinitrogen monoxideN 2 O 2. phosphourus trichloridePCl 3 3. sulfur hexaflurorideSF 6 4. carbon disulfideCS 2 5. carbon tetrabromideCBr 4 6. dinitrogen tetrahydrideN 2 H 4 7. boron trichlorideBCl 3 8. diphosphourus trioxideP 2 O 3 9. hexaselenium monochlorideS 6 Cl

Molecular Compounds –Diatomic molecules –2 of the same nonmetals covalently bonded –are gases –(ex. H 2 = hydrogen gas)

PxQyAcid Compound 2 of Same Elements? >2 Elements? P=Metal? No Yes Name Binary Molecule -use Prefixes P=H? Name Diatomic Molecule

Practice by naming these: lN2OlN2O l NO 2 l Cl 2 O 7 l CBr 4 l CO 2 l BaCl 2 (This one will not use prefixes, since it is an ionic compound!) = dinitrogen monoxide (also called nitrous oxide or laughing gas) = nitrogen dioxide = dichlorine heptoxide = carbon tetrabromide = carbon dioxide

Write formulas for these: l diphosphorus pentoxide l tetraiodine nonoxide l sulfur hexafluoride l nitrogen trioxide l carbon tetrahydride l phosphorus trifluoride l aluminum chloride (Ionic compound)

Answers l P 2 O 5 l I 4 O 9 l SF 6 l NO 3 l CH 4 l PF 3 l AlCl 3