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Molecules and Ions
Image courtesy of www.lab-initio.com
MoleculesTwo 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
Covalent Network Substances
Covalent network substances have covalently bonded atoms, but do not have discrete formulas.
Why Not??
Graphene – carbon allotrope
IonsIons
Cation: A positive ionMg2+, NH4
+
Anion: A negative ionCl-, SO4
2-
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).
Predicting Ionic Charges
Group 1: Lose 1 electron to form 1+ ions H+ Li+ Na+ K+ Rb+ Cs+
Predicting Ionic Charges
Group 2: Loses 2 electrons to form 2+ ions
Be2+ Mg2+ Ca2+ Sr2+ Ba2+
Predicting Ionic ChargesGroup 13: Loses 3 electrons to form 3+ ions
B3+ Al3+ Ga3+
Predicting Ionic ChargesGroup 14: Loses 4 electrons or gains 4 electrons
Caution! C22- and C4-
are both called carbide
Predicting Ionic ChargesGroup 15: Gains 3 electrons to form 3- ions
N3-
P3-
As3-
NitridePhosphide
Arsenide
Predicting Ionic ChargesGroup 16: Gains 2 electrons to form 2- ions
O2-
S2-
Se2-
Oxide
SulfideSelenide
Predicting Ionic ChargesGroup 17: Gains 1 electron to form 1- ions
F1-
Cl1-
Br1-
Fluoride
Chloride
Bromide
I1- Iodide
Predicting Ionic ChargesGroup 18: Stable Noble gases do not form ions!
Predicting Ionic ChargesGroups 3 - 12: Many transition metals have more than one possible oxidation state.
Iron(II) = Fe2+ Iron(III) = Fe3+
Predicting Ionic ChargesGroups 3 - 12: Some transition metals have only one possible oxidation state. Zinc = Zn2+ Silver = Ag+
Writing Ionic Compound Formulas
Example: Barium nitrate
1. Write the formulas for the cation and anion, including CHARGES!
Ba2+ NO3-
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.
Not balanced
( )
2
Writing Ionic Compound Formulas
Example: Ammonium sulfate
1. Write the formulas for the cation and anion, including CHARGES!
NH4+ SO4
2-
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.
Not balanced
( )2
Writing Ionic Compound Formulas
Example: Iron(III) chloride
1. Write the formulas for the cation and anion, including CHARGES!
Fe3+ Cl-
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.
Not balanced
3
Writing Ionic Compound Formulas
Example: Aluminum sulfide
1. Write the formulas for the cation and anion, including CHARGES!
Al3+ S2-
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.
Not balanced
2 3
Writing Ionic Compound Formulas
Example: Magnesium carbonate
1. Write the formulas for the cation and anion, including CHARGES!
Mg2
+CO3
2-
2. Check to see if charges are balanced.
They are balanced
Writing Ionic Compound Formulas
Example: Zinc hydroxide
1. Write the formulas for the cation and anion, including CHARGES!
Zn2+ OH-
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.
Not balanced
( )2
Writing Ionic Compound Formulas
Example: Aluminum phosphate
1. Write the formulas for the cation and anion, including CHARGES!
Al3+ PO43-
2. Check to see if charges are balanced.
They ARE balanced
Naming Ionic CompoundsNaming Ionic CompoundsCation first, then anion
Monatomic cation = name of the element
Ca2+ = calcium ion
Monatomic anion = root + -ideCl- = chloride
CaCl2 = calcium chloride
Naming Ionic CompoundsNaming Ionic Compounds
some metal forms more than one cation
use Roman numeral in name
PbCl2
Pb2+ is cation
PbCl2 = lead(II) chloride
Metals with multiple oxidation states
Binary Molecular CompoundsBinary 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
List of Prefixes
1 = mon(o) 2 = di 3 = tri 4 = tetra 5 = penta 6 = hexa 7 = hepta 8 = octa 9 = nona 10 = deka
Naming Binary Compounds
Naming Binary Compounds
P2O5 =
CO2 =
CO =
N2O =
diphosphorus pentoxide
carbon dioxide
carbon monoxide
dinitrogen monoxide
Practice – Write the FormulaCompound 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
Answers – Write the FormulaCompound 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
Practice – Name the Compounds
Compound Formula
Compound Name
N2O4
SO3
NO
NO2
As2O5
PCl3
CCl4
H2O
SeF6
Check next slide for answers
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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