1. 1 Writing Chemical Formulas General Chemistry Mrs. Amy Nare http://chem.pdx.edu/~wamserc/C335W00/gifs/MW2.gif

2. 2 Objectives Distinguish between molecular and ionic compounds Distinguish between molecular and ionic compounds Contrast molecular formulas and formula units Contrast molecular formulas and formula units Use the periodic table to determine the charge on an ion Use the periodic table to determine the charge on an ion Define monatomic and polyatomic ion and name the charges of common polyatomic ions Define monatomic and polyatomic ion and name the charges of common polyatomic ions Write the formulas and names for binary and ternary ionic compounds Write the formulas and names for binary and ternary ionic compounds Write formulas and names for molecular compounds Write formulas and names for molecular compounds

3. 3 Inspiration Concept Map

4. 4 Chemical Bonding Atoms – same number of protons (+) and electrons (-); electrically neutral Atoms – same number of protons (+) and electrons (-); electrically neutral Ions – atoms w/ a (+) or (-) charge; have lost or gained electrons (e-) Ions – atoms w/ a (+) or (-) charge; have lost or gained electrons (e-) * Cations: (+) charge; has lost e-; metals * Cations: (+) charge; has lost e-; metals * Anions: (-) charge; has gained e-; * Anions: (-) charge; has gained e-; nonmetals nonmetals

5. 5 Chemical Bonding Types of Compounds Types of Compounds A. Molecular – atoms bonded together by shared pairs of e- (covalent bonds); formed between nonmetals ex: C 6 H 12 O 6 B. Ionic – ions attracted to each other by opposite charges; formed between a metal and a nonmetal ex: NaCl

6. 6 Chemical Bonding CompoundMolecularIonic Smallest unit Molecule Formula unit Types of elements Nonmetals Metal cations Nonmetal anions Physical state @ room. temp. Solid, gas, or liquid Solid Boiling point High, >300 o C Low, <300 o C

7. 7 Chemical Bonding Chemical Formulas – show the type and number of atoms in smallest unit of substance Molecular Formula – type and number of atoms joined to form a molecule Molecular Formula – type and number of atoms joined to form a molecule ex: C 2 H 5 OH ex: C 2 H 5 OH Formula Unit – smallest ratio of ions in an ionic compound Formula Unit – smallest ratio of ions in an ionic compound ex: CaF 2 ex: CaF 2

8. 8 Representing Chemical Compounds Law of Definite Proportions – in any sample of a compound, the elements are always combined in the same proportions Law of Definite Proportions – in any sample of a compound, the elements are always combined in the same proportions ex: H 2 O and H 2 O 2 ex: H 2 O and H 2 O 2 H 2 O – water – H:O ratio always 2:1 H 2 O 2 – hydrogen peroxide – H:O ratio always 1:1

9. 9 Identifying Ionic Charges Group A elements – use the periodic table to determine ionic charge Group A elements – use the periodic table to determine ionic charge * elements in same group have same ionic charge same ionic charge * Group 4A and Noble gases – almost never form ions almost never form ions Group B elements – many have more than one ionic charge Group B elements – many have more than one ionic charge

10. 10 Identifying Ionic Charges http://wps.prenhall.com/wps/media/objects/476/488316/ch04.html Charge on cations corresponds to group #. Charge on anions is found by subtracting 8 by group number the number 8 is used b/c it represents # of valence e- in Noble gases the number 8 is used b/c it represents # of valence e- in Noble gases

11. 11 Naming Cations and Anions Monatomic Ions Ions formed by one element Ions formed by one element Cations Cations * for Group A elements – just write * for Group A elements – just write element’s name element’s name ex: calcium ion (Ca 2+) = calcium * for Group B elements – write element’s * for Group B elements – write element’s name, then Roman numerals in name, then Roman numerals in parentheses to denote charge parentheses to denote charge ex: Fe 2+ = Iron (II) and Fe 3+ = Iron (III) Anions – drop the end of the element’s name & add “–ide” ending Anions – drop the end of the element’s name & add “–ide” ending ex: chlorine ion (Cl 1- ) = chloride

12. 12 Naming Cations and Anions Polyatomic Ions Ions formed by more than one type of element Ions formed by more than one type of element Atoms of different elements held together by covalent bonds Atoms of different elements held together by covalent bonds Atoms always stay together and collectively have a single charge Atoms always stay together and collectively have a single charge Do not always have “-ide” ending Do not always have “-ide” ending ex: NH 4 1- = ammonium ion CO 3 2- = carbonate ion CO 3 2- = carbonate ion Learn names, formulas, and charges of polyatomic ions!

13. 13 Naming Cations and Anions Potassium ion Potassium ion Copper (II) ion Copper (II) ion Chloride ion Chloride ion Oxide ion Oxide ion Ba 2+ Ba 2+ S 2- S 2- Au 3+ Au 3+ Nitrite ion Nitrite ion Hydroxide ion Hydroxide ion Phosphate ion Phosphate ion SO 4 2- SO 4 2- CrO 4 2- CrO 4 2- ClO 3 2- ClO 3 2-

14. 14 Binary Ionic Compounds Compounds composed of 2 different monatomic elements Compounds composed of 2 different monatomic elements To write binary formulas – write cation first, then anion To write binary formulas – write cation first, then anion *criss-cross charges to determine how many of each ion you need many of each ion you need *use subscripts to denote number of ions *use subscripts to denote number of ions ex: Ca 2+ + Cl 1- CaCl 2 ex: Ca 2+ + Cl 1- CaCl 2 Na 1+ + Cl 1- NaCl To name binary compounds – write name of cation first, then anion (-ide) To name binary compounds – write name of cation first, then anion (-ide) ex: CaCl 2 = calcium chloride Li 2 O = lithium oxide Li 2 O = lithium oxide

15. 15 Ternary Ionic Compounds Compounds containing at least one polyatomic ion; at least 3 different elements Compounds containing at least one polyatomic ion; at least 3 different elements To write ternary formulas: write cation first, then anion To write ternary formulas: write cation first, then anion *criss-cross charges to determine how *criss-cross charges to determine how many of each ion you need many of each ion you need *use subscripts to denote number of ions *use subscripts to denote number of ions *must use parentheses around polyatomic if more than one is *must use parentheses around polyatomic if more than one is needed!!! needed!!! ex: Na 1+ + SO 3 2- Na 2 SO 3 Mg 2+ + OH 1- Mg(OH) 2 [not same as MgOH 2 ] Mg 2+ + OH 1- Mg(OH) 2 [not same as MgOH 2 ] To name ternary compounds: write name of cation, then name of anion (not all end in “-ide”) To name ternary compounds: write name of cation, then name of anion (not all end in “-ide”) **be careful with transition metals (more than one charge)** ex: CaCO 3 = calcium carbonate PbSO 4 = lead (II) sulfate Ag 2 CrO 4 = silver chromate

16. 16 Ionic Compounds NaNO 3 NaNO 3 CaSO 4 CaSO 4 (NH 4 ) 2 O (NH 4 ) 2 O CuSO 3 CuSO 3 Fe(OH) 3 Fe(OH) 3 NaF NaF Lithium sulfide Lithium sulfide Iron (III) phosphide Iron (III) phosphide Magnesium fluoride Magnesium fluoride Barium nitrate Barium nitrate Aluminum hydroxide Aluminum hydroxide Potassium phosphate Potassium phosphate Practice making ionic compounds!

17. 17 Binary Molecular Compounds Two nonmetals joined by covalent bonds Two nonmetals joined by covalent bonds Use prefixes for naming Use prefixes for naming 1 = mono- 2 = di- 3 = tri- 4 = tetra- 5 = penta- 6 = hexa- 7 = hepta- 8 = octa- 9 = nona- 10 = deca-

18. 18 Binary Molecular Compounds To name binary molecular compounds: To name binary molecular compounds: *first element gets a prefix if there is more than one *second element ALWAYS gets prefix, and “-ide” ending ex: N 2 O 3 = dinitrogen trioxide CO = carbon monoxide (not monocarbon) CO = carbon monoxide (not monocarbon) If element begins with vowel and prefix ends in “a” or “o”, then drop last vowel on prefix to form the name If element begins with vowel and prefix ends in “a” or “o”, then drop last vowel on prefix to form the name ex: Cl 2 O 7 = dichlorine heptoxide (not heptaoxide) ex: Cl 2 O 7 = dichlorine heptoxide (not heptaoxide)

19. 19 Molecular Compounds P 2 O 5 P 2 O 5 N 2 O N 2 O NO 2 NO 2 CBr 4 CBr 4 CO 2 CO 2 tetraiodine nonoxide tetraiodine nonoxide sulfur hexafluoride sulfur hexafluoride nitrogen trioxide nitrogen trioxide carbon tetrahydride carbon tetrahydride phosphorus trifluoride phosphorus trifluoride

20. 20 Assess what you learned. Log on to the Internet and take the quiz. Assess what you learned. Log on to the Internet and take the quiz. http://school.discovery.com/quizzes31/amy_trauth/ FormulasQuiz.html http://school.discovery.com/quizzes31/amy_trauth/ FormulasQuiz.html

21. 21 Websites on Writing Formulas