1. Compounds: Introduction to Bonding
Most elements exist as compounds in combination with
other elements
Compounds are formed by an exchange of electrons
Two types of compounds:
• Ionic: as a result of transferring electrons
• Covalent: as a result of sharing electrons
Ionic Compounds: Formation
Ions: charged particles formed from atoms or groups of
atoms
Cations (+): positively charged ions (i.e. from metals)
Anions (-): negatively charged ions (i.e. from non-metals)
Ionic “bonding” is a result of electrostatic attraction
E ! charge(1)"charge(2)
distance
2. All elements want to be like noble gases
that is, to have the same number of electrons
(the same electronic configuration)
Example: Sodium Chloride, NaCl, Na+Cl- :
Na(11 electrons) - 1 e- = Na+ (10 electrons); like Ne
Cl (17 electrons) + 1 e- = Cl- (18 electrons); like Ar
Ionic Compounds: Formation
3. All elements want to be like noble gases
that is, to have the same number of electrons
Main group elements:
Group 1 alkali metals: lose one electron # M+
Group 2 alkaline earth metals: lose two electrons # M2+
Group 3 metals: lose three electrons # M3+
Ionic Compounds: Formation
All elements want to be like noble gases
that is, to have the same number of electrons
Main group elements:
Group 7 halogens: acquire one electron # A-
Group 6 elements: acquire two electrons # A2-
Group 5 elements: acquire three electrons # A3-
Ionic Compounds: Formation
4. But a continuous network of ions
Ionic Compounds: Structure
NO bonds in solid or liquid state
NaCl
Covalent Compounds:
Real Bonds
Simplest case: Hydrogen
H• + H• = H:H = H2 compare to He:
Non-metals SHARE electrons to attain the nearest
noble gas electron count (electronic configuration).
5. Covalent Compounds:
Real Bonds
Another example: Oxygen
O: + O: = O::O = O2 compare to Ne
Non-metals SHARE electrons to attain the nearest
noble gas electron count (electronic configuration).
Non-metals SHARE electrons to attain the nearest
noble gas electron count (electronic configuration).
Covalent Compounds:
Real Bonds
More complex example: Oxygen and Hydrogen
H• + •O• + •H = H:O:H = H-O-H = H2O
6. Key Distinction
Covalent Compounds Are Molecules
ionic compounds do not have molecules
(solid or liquid)
Polyatomic Ions
hydroxide OH–
sulfate SO4
2–
nitrate NO3
–
phosphate PO4
3–
carbonate CO3
2–
bicarbonate HCO3
–
dichromate Cr2O7
2–
perchlorate ClO4
–
permanganate MnO4
–
acetate CH3CO2
–
Common Anions Common Cations
ammonium NH4
+
hydronium H3O +
and metals
Fe2+ iron (II) or ferric
Fe3+ iron (III) or ferrous
Cu+ copper (I) or cupric
Cu2+ copper (II) or cuprous
7. Chemical Formulas
empirical formula shows the relative number
of atoms in a compound; derives from the masses of
the component elements - elemental analysis
Acetic acid CH2O
molecular formula shows the actual number of
atoms in a compound
Acetic acid C2H4O2 or (CH3CO2H)
(extended)
Chemical Formulas:
Structural
structural formula is the most comprehensive
representation of a compound, defines completely the
number of atoms and their connectivity
H
C
H
CH
O
O
H
Acetic acid, C2H4O2 (CH3CO2H):
Structural
formula
9. Chemical Formulas:
Molecular
(NH4)2HPO4 = N2H9PO4
Ca3(PO4)2 = Ca3P2O8
Ce(NH4)2(NO3)6 = CeN8H8O18
Some Nomenclature
! In ionic compounds, the cation goes first, the anion follows
i.e. ammonium phosphate (NH4
+)3PO4
3–
! Metal cations: the same as the name of the metal
i. e. lithium # lithium chloride LiCl; lead # lead (II) iodide PbI2
! Monoatomic anions: root + -ide
i.e. chlorine # lithium chloride; oxygen # titanium oxide TiO2
! Polyatomic anions: oxoanions with more O root + ate,
otherwise root + ite
i.e. sulfate (SO4
2–) sulfite (SO3
2–); nitrate (NO3
–) nitrite (NO2
–)
10. Some Nomenclature:
Acids
! Polyatomic anions are formed from acids
anion ends with -ate; acid ends with -ic
anion ends with -ite; acid ends with -ous
NO3
- nitrate HNO3 nitric acid
SO4
2- sulfate H2SO4 sulfuric acid
PO4
3- phosphate H3PO4 phosphoric acid
SO3
2- sulfite H2SO3 sulfurous acid
CO3
2- carbonate H2CO3 carbonic acid
! Binary acids:
hydrofluoric acid HF
hydrochloric acid HCl
hydrobromic acid HBr
hydroiodic acid HI
Some Nomenclature:
Binary Covalent Compounds
! In the same period, the element on the left side is the first
word in the name; if in the same period, the element with the
higher period number (lower in the periodic table) goes first
!The second element: root + ide
! Only If more than one element present in the first word,
there is a greek numerical prefix to indicate the number of
atoms. The second element usually has a prefix.
11. Some Nomenclature:
Binary Covalent Compounds
CO carbon monoxide
CO2 carbon dioxide
SO3 sulfur trioxide
S2Cl2 disulfur dichloride
Cl2O7 dichlorine heptaoxide
N2O4 dinitrogen tetraoxide
N2O dinitrogen oxide
Alkanes: page 71
How to predict the composition of
ionic compounds from names
The charges must be balanced!
Net charge is zero
Example: aluminum hydroxide
12. How to predict the composition of
ionic compounds
The charges must be balanced!
Net charge is zero
Example: aluminum hydroxide
Aluminum is Al3+
Hydroxide is OH–
Al(OH)3
AlOH3 is incorrect
H O
How to predict the composition of
ionic compounds
The charges must be balanced!
Net charge is zero
Example: iron (III) [ferric] oxide
13. How to predict the composition of
ionic compounds
The charges must be balanced!
Net charge is zero
Example: iron (III) [ferric] oxide
Iron (III) is Fe3+
oxide is O2–
balance: Fe2O3
Fe2(O)3 is incorrect
How to predict the composition of
ionic compounds
The charges must be balanced!
Net charge is zero
Example: zinc carbonate
14. How to predict the composition of
ionic compounds
The charges must be balanced!
Net charge is zero
Example: zinc carbonate
Zinc is Zn2+
carbonate is CO3
2–
balance: ZnCO3
Zn(CO3), Zn(CO3)1 are incorrect
2-
carbonate
How to predict the composition of
ionic compounds
The charges must be balanced!
Net charge is zero
Example: cesium carbonate
2-
carbonate
15. How to predict the composition of
ionic compounds
The charges must be balanced!
Net charge is zero
Example: cesium carbonate
Cesium is Cs+
carbonate is CO3
2–
balance: Cs2CO3
Cs2(CO3), Cs2(CO3)1, (Cs)2CO3
are all incorrect
2-
carbonate
Molecular Weight (MW or FW)
molecular mass (weight) = sum of all atomic masses
Molecular Weight (Mass) is the same thing
as Formula Weight (Mass)
[ FW ]
NaCl
Molecular Mass of H2O is 2"1.008 + 16.00 = 18.02
16. Molecular Weight (MW)
What is the molecular weight of aluminum sulfate?
Molecular Weight (MW)
What is the molecular weight of aluminum sulfate?
• Aluminum sulfate is Al2(SO4)3
• FW[SO4] = 32.07 + 4"16.00 =
• FW[Al2(SO4)3] = 2"26.98 + 3"96.07 =
96.07
342.17
17. Molecular Weight (MW)
What is the molecular weight of aluminum sulfate?
• Aluminum sulfate is Al2(SO4)3
• Al2(SO4)3 = Al2S3O12
• FW[Al2(SO4)3] = 2"26.98 + 3"32.07 + 12"16.00 = 342.17
Molecular Weight (MW)
What is the molecular weight of copper (II) sulfate
pentahydrate?
• CuSO4•5H2O
• FW[CuSO4•5H2O] = 63.55 + 96.07 + 5"18.02 = 249.72
18. Mixtures
• heterogeneous
has boundaries between component (phase separation)
• homogeneous
no boundaries between component (phase separation)
solutions: liquid mixtures
aqueous solutions: the solvent is water
Mixtures: Separation
• filtration
• crystallization
• distillation
• extraction
• chromatography
19. Mixtures: Separation
• filtration (heterogeneous)
based on the difference in the state of matter (solid/liquid)
Mixtures: Separation
• crystallization (heterogeneous)
based on the difference in solubility
21. Mixtures: Separation
• extraction (homogeneous)
based on the difference
in solubility
(organic/aqueous)
Mixtures: Separation
• chromatography (homogeneous)
based on the difference in solubility (organic/aqueous)
and absorbance on immobile phase
