1. Representing Chemical Compounds
Naming Compounds and Writing Chemical Formulas

2. Chemical Formula
Shows the kinds and numbers of atoms in the smallest representative unit of the substance.
If only one atom of the element in a compound, you only write the element’s symbol. (Ex: Lithium fluoride  LiF)
If the molecules of the element each have more than one atom, a number is used as a subscript. (Ex: Lithium oxide  Li2O).

3. Molecular Formulas
Chemical formula for a molecular compound is called a molecular formula.
Shows the kinds and numbers of atoms present in a molecule of a compound.
Examples: CO, CO2
Tells nothing about the structure of the molecule --- doesn’t show arrangement of the various atoms.

4. Molecular Formulas (continued)
Refer to page 129, Figures 6.6 – 6.8.
Use models and/or diagrams to show the arrangements of molecules in a molecular compound.
IMPORTANT NOTE: Be familiar with the various types of representations of molecular compounds: Molecular formula, Space-filling molecular model, Perspective Drawing, Ball-and-Stick Molecular Model.

5. Formula Units Chemical formulas represent ionic compounds.
Formula units – lowest whole-number ration of ions in the compound.

6. Laws of Definite and Multiple Proportions
Law of Definite Proportions: in samples of any chemical compound, the masses of the elements are always in the same proportions.
Law of Multiple Proportions: whenever two elements form more than one compound, the different masses of one element that combine with the same mass of the other element are in the ratio of small whole numbers.
Refer to page 142, Practice Problems.

7. Ionic Charges
For most of the Group A elements, the Periodic Table can tell what kind of ion they will form from their location.
Elements in the same group have similar properties.
Including the charge when they are ions.

8. +1 +2 +3 -3 -2 -1

9. Naming ions We will use the systematic way.
Cation- if the charge is always the same (Group A) just write the name of the metal.
Transition metals can have more than one type of charge.
Indicate the charge with roman numerals in parenthesis.

10. Name These
Na+1
Ca+1
Al+3
Fe+3
Fe+2
Pb+3
Li+1

11. Write Formulas for these
Potassium ion
Magnesium ion
Copper (II) ion
Chromium (VI) ion
Barium ion
Mercury (II) ion

12. Naming Anions Anions are always the same.
Change the element ending to – ide.
F-1 Fluorine
F-1 Fluoride

13. Name These
N-3
Br-1
O-2
Ga+3

14. Write These
Sulfide ion
iodide ion
phosphide ion
Strontium ion

15. Polyatomic Ions
Groups of atoms that stay together and have a charge.

16. Ions in Ionic Compounds

17. Naming Binary Ionic Compounds
Binary Compounds - 2 elements.
Ionic - a cation and an anion.
To write the names just name the two ions.
Easy with Representative elements.
Group A
NaCl = Na+ Cl- = sodium chloride
MgBr2 = Mg+2 Br- = magnesium bromide

18. Naming Binary Ionic Compounds
The problem comes with the transition metals.
Need to figure out their charges.
The compound must be neutral.
same number of + and – charges.
Use the anion to determine the charge on the positive ion.

19. Naming Binary Ionic Compounds
Write the name of CuO
Need the charge of Cu
O is -2
copper must be +2
Copper (II) chloride
Name CoCl3
Cl is -1 and there are three of them = -3
Co must be +3 Cobalt (III) chloride

20. Naming Binary Ionic Compounds
Write the name of Cu2S.
Since S is -2, the Cu2 must be +2, so each one is +1.
copper (I) sulfide
Fe2O3
Each O is x -2 = -6
3 Fe must = +6, so each is +2.
iron (III) oxide

21. Naming Binary Ionic Compounds
Write the names of the following
KCl
Na3N
CrN
Sc3P2
PbO
PbO2
Na2Se

22. Ternary Ionic Compounds
Will have polyatomic ions
At least three elements
name the ions
NaNO3
CaSO4
CuSO3
(NH4)2O

23. Ternary Ionic Compounds
LiCN
Fe(OH)3
(NH4)2CO3
NiPO4

24. Writing Formulas The charges have to add up to zero.
Get charges on pieces.
Cations from name of table.
Anions from table or polyatomic.
Balance the charges by adding subscripts.
Put polyatomics in parenthesis.

25. Writing Formulas Write the formula for calcium chloride.
Calcium is Ca+2
Chloride is Cl-1
Ca+2 Cl-1 would have a +1 charge.
Need another Cl-1
Ca+2 Cl 2-

26. Write the formulas for these
Lithium sulfide
tin (II) oxide
tin (IV) oxide
Magnesium fluoride
Copper (II) sulfate
Iron (III) phosphide
gallium nitrate
Iron (III) sulfide

27. Write the formulas for these
Ammonium chloride
ammonium sulfide
barium nitrate

28. Things to look for If cations have (), the number is their charge.
If anions end in -ide they are probably off the periodic table (Monoatomic)
If anion ends in -ate or -ite it is polyatomic

29. Writing names and Formulas
Molecular Compounds
Writing names and Formulas

30. Molecular compounds made of just nonmetals
smallest piece is a molecule
can’t be held together because of opposite charges.
can’t use charges to figure out how many of each atom

31. Easier Molecular compounds name tells you the number of atoms.
Ionic compounds use charges to determine how many of each.
Have to figure out charges.
Have to figure out numbers.
Molecular compounds name tells you the number of atoms.
Uses prefixes to tell you the number

32. Prefixes 1 mono- 2 di- 3 tri- 4 tetra- 5 penta- 6 hexa- 7 hepta-
8 octa-

33. Prefixes
9 nona-
10 deca-
To write the name write two words

34. Prefixes 9 nona- 10 deca- To write the name write two words
Prefix name Prefix name -ide

35. Prefixes 9 nona- 10 deca- To write the name write two words
One exception is we don’t write mono- if there is only one of the first element.

36. Prefixes 9 nona- 10 deca- To write the name write two words
One exception is we don’t write mono- if there is only one of the first element.
No double vowels when writing names (oa oo)

37. Name These
N2O
NO2
Cl2O7
CBr4
CO2
BaCl2

38. Write formulas for these
diphosphorus pentoxide
tetraiodide nonoxide
sulfur hexaflouride
nitrogen trioxide
Carbon tetrahydride
phosphorus trifluoride
aluminum chloride

39. Writing names and Formulas
Acids
Writing names and Formulas

40. Acids Compounds that give off hydrogen ions when dissolved in water.
Must have H in them.
will always be some H next to an anion.
The anion determines the name.

41. Naming acids
If the anion attached to hydrogen is ends in -ide, put the prefix hydro- and change -ide to -ic acid
HCl - hydrogen ion and chloride ion
hydrochloric acid
H2S hydrogen ion and sulfide ion
hydrosulfuric acid

42. Naming Acids If the anion has oxygen in it it ends in -ate of -ite
change the suffix -ate to -ic acid
HNO3 Hydrogen and nitrate ions
Nitric acid
change the suffix -ite to -ous acid
HNO2 Hydrogen and nitrite ions
Nitrous acid

43. Name these HF
H3P
H2SO4
H2SO3
HCN
H2CrO4

44. Writing Formulas Hydrogen will always be first
name will tell you the anion
make the charges cancel out.
Starts with hydro- no oxygen, -ide
no hydro, -ate comes from -ic, -ite comes from -ous

45. Write formulas for these
hydroiodic acid
acetic acid
carbonic acid
phosphorous acid
hydrobromic acid