Transcript General Chemistry

Chapter 3
Chemical Compounds
Jons J. Berzelius 1779-1848.
Accurately determined
atomic weights, used in
future Periodic Table.
Originated modern chemical
formulas, including “K” and
“Na” for potassium and sodium.
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Molecules and Molecular Compounds
Molecules and Chemical Formulas
Molecules are assemblies of two or more atoms
bonded together.
Each molecule has a chemical formula.
The chemical formula indicates:
which atoms are found in the molecule, and
in what proportion they are found.
Compounds formed from molecules are
molecular compounds.
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Molecules and Molecular Compounds
Molecular and Empirical Formulas
Molecular formulas
give the actual numbers and types of atoms in a molecule.
Examples:
H2O, CO2, CO, CH4, H2O2, O2, O3, and C2H4.
Empirical formulas
give the relative numbers and types of atoms in a molecule.
That is, they give the lowest whole number ratio of atoms
in a molecule.
Examples: H2O, CO2, CO, CH4, HO, CH2.
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Molecules and Molecular Compounds
Picturing Molecules
Molecules occupy three dimensional space. However, we
often represent them in two dimensions.
The structural formula gives the connectivity between
individual atoms in the molecule.
The structural formula may or may not be used to show
the three dimensional shape of the molecule.
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Molecules and Molecular Compounds
Picturing Molecules
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Different representations of methane (CH4)
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Ions and Ionic Compounds
When an atom or molecule loses electrons, it becomes
positively charged.
•For example, when Na loses an electron, it becomes Na+.
Positively charged ions are called cations.
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Ions and Ionic Compounds
When an atom or molecule gains electrons, it becomes
negatively charged.
For example when Cl gains an electron it becomes Cl-.
Negatively charged ions are called anions.
An atom or molecule can lose more than one electron.
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Ions and Ionic Compounds
When an atom or molecule loses two electrons, it
becomes doubly positively charged.
For example, when Mg loses two electrons, it becomes Mg2+
12p+
12 e-
Mg atom
“magnesium atom”
lose 2 e-
12p+
10 e-
2+
Mg
ion
“magnesium ion”
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Ions and Ionic Compounds
When an atom or molecule gains two electrons, it
becomes doubly negatively charged.
For example, when S gains 2 electrons, it becomes S2-
16 p+
16 e-
S atom
“sulfur atom”
gain 2 e-
16p+
2S
18 e-
ion
“sulfide ion”
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Ions and Ionic Compounds
Predicting Ionic Charge
The number of electrons an atom gains or loses is
related to its position on the periodic table.
Metals tend to form cations whereas non-metals tend
to form anions.
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Ions and Ionic Compounds
What ions do the main group elements (the “A”
elements) form? It depends on their grouping.
Group IA elements (H, Li, Na..) form 1+ ions (H+,Li+, Na+…)
Group IIA elements (Be, Mg, Ca)form 2+ ions (Be2+, Mg2+…)
Group IIIA elements (B, Al, Ga) form 3+ ions (B3+, Al3+, …)
Group VA elements (N, P…) form 3- ions (N3-, P3-)
Group VIA elements (O, S,..) form 2- ions (O2-, S2-…)
Group VIIA elements (F, Cl, Br.) form 1- ions (F-, Cl-, Br-….)
Group VIIIA elements do not form ions.
Neither does Group IVA.
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Ions and Ionic Compounds
Ionic Compounds
The majority of chemistry involves the transfer of
electrons between species.
Example:
To form NaCl, the neutral sodium atom, Na, must lose an
electron to become a cation: Na+
.
Na
p+
11
11 e-
.
11 p+
10 e-
Na+
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Ions and Ionic Compounds
Ionic Compounds
whereas non-metals tend to form anions.
The electron cannot be lost entirely, so it is transferred to a
chlorine atom, Cl, which then becomes an anion: Cl-.
.
Cl
(from Na atom)
Cl-
17 p+
17 e-
17 p+
18 eThe Na+ and Cl- ions are attracted to form an ionic NaCl
lattice which crystallizes.
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Ions and Ionic Compounds
Important: note that there are no easily identified NaCl
molecules in the ionic lattice. Therefore, we cannot use
molecular formulas to describe ionic substances.
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Ions and Ionic Compounds
Ionic Compounds
Consider the formation of Mg3N2:
Mg loses two electrons to become Mg2+
Nitrogen gains three electrons to become N3-.
For a neutral species, the number of electrons lost and
gained must be equal.
However, Mg can only lose electrons in twos and N can
only accept electrons in threes.
Therefore, Mg needs to lose 6 electrons (2  3) and N
gain those 6 electrons (3  2).
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Ions and Ionic Compounds
Ionic Compounds
I.e., 3Mg atoms need to form 3Mg2+ ions (total 3x2+
charges) and 2 N atoms need to form 2N3- ions (total
2x3- charges).
Therefore, the formula is Mg3N2.
2+
Mg
Mg 3 N 2
3N
MgO
Be careful! what’s the ionic compound formed between
magnesium and oxygen?)
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Naming Inorganic Compounds
Names and Formulas of Ionic Compounds
Naming of compounds, nomenclature, is divided into
organic compounds (those containing C) and inorganic
compounds (the rest of the periodic table)
Cations formed from a metal have the same name
as the metal.
Example: Na+ = sodium ion.
If the metal can form more than one cation, then the
charge is indicated in parentheses in the name.
Examples: Cu+ = copper(I); Cu2+ = copper(II).
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Hydrogen ion
Lithium ion
Sodium ion
Potassium ion
Silver ion
Magnesium ion
Calcium ion
Strontium ion
Barium ion
Zinc ion
Cadmium ion
Aluminum ion
H+
Li+
Na+
K+
Ag+
Mg2+
Ca2+
Sr2+
Ba2+
Zn2+
Cd2+
Al3+
Cupric ion Co2+
Cuprous ion Cu+
Ferric ion Fe3+
Ferrous ion Fe2+
Manganous ion Mn2+
Mercurous ion Hg22+
Mercuric ion Hg2+
Nickelous ion Ni2+
Plumbous ion Pb2+
Stannous ion Sn2+
Stannic ion Sn4+
Chromic ion Cr3+
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Naming Inorganic Compounds
Names and Formulas of Ionic Compounds
Monoatomic anions (with only one atom) are called -ide.
Example: Cl- is chloride ion.
Exceptions: hydroxide (OH-), cyanide (CN-), peroxide (O22-).
Polyatomic anions (with many atoms) containing oxygen
end in -ate or -ite. (The one with more oxygen is called ate.)
Examples: NO3- is nitrate, NO2- is nitrite.
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Naming Inorganic Compounds
nitrate
NO3hydroxide OHnitrite
NO2phosphate PO43carbonate CO32ammonium NH4+
sulfate
SO42perchlorate ClO4sulfite
SO32chlorate
ClO3cyanide
CN chlorite
ClO2chromate CrO4-2
hypochlorite ClO dichromate Cr2O72carbonate CO32permanganate
MnO4bicarbonate (or hydrogen carbonate) HCO321
Monoatomic ions
Hydride
fluoride
chloride
bromide
iodide
HFCl Br I-
oxide
peroxide
sulfide
nitride
O2O22S2N3-
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Names and Formulas of Binary Molecular Compounds
Binary molecular compounds have two elements.
The most metallic element is usually written first (i.e., the one to the
farthest left on the periodic table). Exception: NH3.
If both elements are in the same group, the lower one is written first.
Greek prefixes are used to indicate the number of atoms.
mono
di
tri
tetra
penta
hexa
hepta
octa
nona
deca
1
2
3
4
5
6
7
8
9
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Name: NO2
Nitrogen dioxide
Sulfur trioxide
SO3
N2O4 Dinitrogen tetroxide
P2O5 Diphosphorus pentoxide
CCl4 Carbon tetrachloride
Carbon monoxide
CO
CO2 Carbon dioxide
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Naming Organic Compounds
Name, formula, bp oC
Name, formula, bp oC
Methane CH4 -162
Methyl alcohol CH3OH, 66
Ethane C2H6 -89
Ethyl alcohol C2H5OH, 98
Propane C3H8 -42
Propyl alcohol C3H7OH, 97
Butane C4H10
0
Isopropyl alcohol
Pentane C5H12 36
CH3-CH(OH)-CH3, 82
Hexane C6H14 69 [Propyl alcohol and isopropyl
Heptane C7H16 98
alcohol are isomers]
Octane C8H18 126
Nonane C9H20 151
Decane C10H22 174
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