Molecules and Ions

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Molecules and Ions
Image courtesy of www.lab-initio.com
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Molecules
Two or more atoms of the same or different
elements, covalently bonded together.
Molecules are discrete structures, and their
formulas represent each atom present in the
molecule.
Pentane, C5H12
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Covalent Network Substances
Covalent network substances have covalently
bonded atoms, but do not have discrete formulas.
Why Not??
Graphene carbon allotrope
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Ions

• Cation A positive ion
• Mg2, NH4
• Anion A negative ion
• Cl-, SO42-
• Ionic Bonding Force of attraction between
  oppositely charged ions.
• Ionic compounds form crystals, so their formulas
  are written empirically (lowest whole number
  ratio of ions).

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Predicting Ionic Charges
Group 1 Lose 1 electron to form 1 ions
H
Li
Na
K
Rb
Cs
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Predicting Ionic Charges
Group 2 Loses 2 electrons to form 2 ions
Be2
Mg2
Ca2
Ba2
Sr2
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Predicting Ionic Charges

Group 13 Loses 3 electrons to form 3 ions
B3
Al3
Ga3
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Predicting Ionic Charges
Group 14
Loses 4 electrons or gains 4
electrons
Caution! C22- and C4- are both called carbide
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Predicting Ionic Charges
Nitride
N3-
Group 15
Gains 3 electrons to form 3- ions
Phosphide
P3-
As3-
Arsenide
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Predicting Ionic Charges
Oxide
O2-
Group 16 Gains 2 electrons to form 2- ions
S2-
Sulfide
Se2-
Selenide
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Predicting Ionic Charges
Group 17 Gains 1 electron to form 1- ions
F1-
Fluoride
Cl1-
Chloride
Br1-
Bromide
I1-
Iodide
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Predicting Ionic Charges
Group 18 Stable Noble gases do not form ions!
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Predicting Ionic Charges
Groups 3 - 12 Many transition metals have more
than one possible oxidation state.
Iron(II) Fe2
Iron(III) Fe3
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Predicting Ionic Charges
Groups 3 - 12 Some transition metals have
only one possible oxidation state.
Zinc Zn2
Silver Ag
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Writing Ionic Compound Formulas
Example Barium nitrate
1. Write the formulas for the cation and anion,
including CHARGES!
2. Check to see if charges are balanced.
3. Balance charges , if necessary, using
subscripts. Use parentheses if you need more than
one of a polyatomic ion.
Ba2
NO3-
( )
2
Not balanced
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Writing Ionic Compound Formulas
Example Ammonium sulfate
1. Write the formulas for the cation and anion,
including CHARGES!
2. Check to see if charges are balanced.
3. Balance charges , if necessary, using
subscripts. Use parentheses if you need more than
one of a polyatomic ion.
NH4
( )
SO42-
2
Not balanced
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Writing Ionic Compound Formulas
Example Iron(III) chloride
1. Write the formulas for the cation and anion,
including CHARGES!
2. Check to see if charges are balanced.
3. Balance charges , if necessary, using
subscripts. Use parentheses if you need more than
one of a polyatomic ion.
Fe3
Cl-
3
Not balanced
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Writing Ionic Compound Formulas
Example Aluminum sulfide
1. Write the formulas for the cation and anion,
including CHARGES!
2. Check to see if charges are balanced.
3. Balance charges , if necessary, using
subscripts. Use parentheses if you need more than
one of a polyatomic ion.
Al3
S2-
2
3
Not balanced
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Writing Ionic Compound Formulas
Example Magnesium carbonate
1. Write the formulas for the cation and anion,
including CHARGES!
2. Check to see if charges are balanced.
Mg2
CO32-
They are balanced
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Writing Ionic Compound Formulas
Example Zinc hydroxide
1. Write the formulas for the cation and anion,
including CHARGES!
2. Check to see if charges are balanced.
3. Balance charges , if necessary, using
subscripts. Use parentheses if you need more than
one of a polyatomic ion.
( )
Zn2
OH-
2
Not balanced
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Writing Ionic Compound Formulas
Example Aluminum phosphate
1. Write the formulas for the cation and anion,
including CHARGES!
2. Check to see if charges are balanced.
Al3
PO43-
They ARE balanced
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Naming Ionic Compounds

• Cation first, then anion
• Monatomic cation name of the element
• Ca2 calcium ion
• Monatomic anion root -ide
• Cl- chloride
• CaCl2 calcium chloride

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Naming Ionic Compounds
Metals with multiple oxidation states

• some metal forms more than one cation
• use Roman numeral in name
• PbCl2
• Pb2 is cation
• PbCl2 lead(II) chloride

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Binary Molecular Compounds

• Compounds between two nonmetals
• First element in the formula is named first.
• Keeps its element name
• Gets a prefix if there is a subscript on it
• Second element is named second
• Use the root of the element name plus the -ide
  suffix
• Always use a prefix on the second element

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List of Prefixes

• 1 mon(o)
• 2 di
• 3 tri
• 4 tetra
• 5 penta
• 6 hexa
• 7 hepta
• 8 octa
• 9 nona
• 10 deka

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Naming Binary Compounds
P2O5
diphosphorus pentoxide
CO2
carbon dioxide
CO
carbon monoxide
N2O
dinitrogen monoxide
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Practice Write the Formula
Compound Name Compound Formula
Carbon dioxide
Carbon monoxide
Diphosphorus pentoxide
Dinitrogen monoxide
Silicon dioxide
Carbon tetrabromide
Sulfur dioxide
Phosphorus pentabromide
Iodine trichloride
Nitrogen triiodide
Dinitrogen trioxide
Check next slide for answers
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Answers Write the Formula
Compound Name Compound Formula
Carbon dioxide CO2
Carbon monoxide CO
Diphosphorus pentoxide P2O5
Dinitrogen monoxide N2O
Silicon dioxide SiO2
Carbon tetrabromide CBr4
Sulfur dioxide SO2
Phosphorus pentabromide PBr5
Iodine trichloride ICl3
Nitrogen triiodide NI3
Dinitrogen trioxide N2O3
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Practice Name the Compounds
Compound Formula Compound Name
N2O4
SO3
NO
NO2
As2O5
PCl3
CCl4
H2O
SeF6
Check next slide for answers
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Answers Name the Compounds
Compound Formula Compound Name
N2O4 dinitrogen tetroxide
SO3 sulfur trioxide
NO nitrogen monoxide
NO2 nitrogen dioxide
As2O5 diarsenic pentoxide
PCl3 phosphorus trichloride
CCl4 carbon tetrachloride
H2O dinitrogen monoxide
SeF6 selenium hexafluoride
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Naming Acids

• 2 classification of acids
• Binary acids contain only 2 elements hydrogen
  and oxygen
• Ternary acids (oxyacids) contain hydrogen and
  a polyatomic ion

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Binary Acids

• To name binary acids, use the name of the anion
  as the root, add the prefix hydro- and the suffix
  ic and then the word acid.
• HCl hydrochloric acid

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Ternary Acids (Oxyacids)

• The most common form of a ternary acid is named
  by adding the suffix ic to the name of the
  polyatomic ion. No prefix is used.
• SO4-2 is the sulfate ion
• H2SO4 is sulfuric acid

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Naming Oxyacids
Ion Symbol Ion Name Acid Formula Acid Name
PO43- phosphate H3PO4 Phosphoric acid
CO32- carbonate H2CO3 Carbonic acid
NO3- nitrate HNO3 Nitric acid
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Naming Oxyacids
Ion Symbol Ion Name Acid Formula Acid Name
ClO- hypochlorite HClO Hypochlorous acid
ClO2- chlorite H ClO2 Chlorous acid
ClO3- chlorate HClO3 Chloric acid
ClO4- perchlorate HClO4 Perchloric acid
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Naming Oxyacids

• If the ion name ends in ate,
• then the acid name ends in ic.
• If the ion name ends in ite,
• Then the acid name ends in ous.