Representing Chemical Compounds

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 elements 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
  --- doesnt 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

• Na1
• Ca1
• Al3
• Fe3
• Fe2
• Pb3
• Li1

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
• Ga3

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 Mg2 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 -2 3 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 Ca2
• Chloride is Cl-1
• Ca2 Cl-1 would have a 1 charge.
• Need another Cl-1
• Ca2 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
Molecular Compounds

• Writing names and Formulas

30
Molecular compounds

• made of just nonmetals
• smallest piece is a molecule
• cant be held together because of opposite
  charges.
• cant use charges to figure out how many of each
  atom

31
Easier

• 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 dont 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 dont 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
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