Navigating the Periodic Table
• Make sure you can locate and identify the various classifications
of the elements.
•
•
•
•
•
Alkali metals: Group 1A
Alkaline earth metals: Group 2A
Halogens: Group 7A
Nobel gases : Group 8A
The 7 diatomic elements MUST
be memorized!
Some metals, metalloids, and nonmetals.
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Elements and Compounds
•
Elements combine chemically
to form compounds.
•
Compounds can be either:
Ionic (salts)- these contain
cations and anions held together
by strong forces of attraction.
or
Covalent-these contain
molecules, individual units
containing atoms held together
through the sharing of electrons
between the atoms.
NaCl (ionic) is formed chemically from sodium and chlorine in a
oxidation-reduction reaction; the result is a solid that contains
oppositely charged ions arrange in an extended three dimensional
pattern called a lattice. There are no discrete molecules in ionic
compounds.
Covalent:
discrete molecules, bonded
atoms are held together in
specific shapes
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Formation of Ionic Compounds
Transferring
electrons from
the atoms of
one element to
those of another
results in an
ionic compound.
Remember that
there are no
molecules in
an ionic
compound.
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Ionic Compounds: Cations + Anions
• Cations are formed when an atom LOSES electrons (oxidation).
•
Cations are (+)
charged ions.
lost e– (to anion)
• Anions are formed when an atom GAINS electrons (reduction).
gained e–
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(from cation)
•
Anions are (–)
charged ions.
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Common Monatomic Cations and Anions
•
•
Metals form cations.
They lose valence shell
electrons = column #.
– Group 1A :
lose how many e–?
– Group 2A:
lose how many e–?
– Metals of group 3A:
lose how many e–?
•
•
Nonmetals form anions
They gain electrons to fill their outer
valence shell (octet rule).
– Group 4A nonmetal:
gain how many e–?
– Group 5A nonmetals:
gain how many e–?
– Group 6A nonmetals:
gain how many e–?
– Group 7A:
gain how many e–?
– H when bonded to a metal: gains
how many e–?
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Some Common Ions
Most main-group elements
form one monatomic ion. Most
transition elements form two
monatomic ions.
Formulas of ionic compounds are empirical formulas, they reflect the smallest
whole number ratio of cations to anions that results in a net charge of zero.
Examples:
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Coulomb’s Law for Charged Particles: IONIC
Attractions!
• The force of attraction between two charged particles is given
by Coulomb’s Law: (Electrostatic force)
(n+e)(n−e)
Force = k
d2
• k is a constant
•
n+ and n- are the magnitude of the (+) and (–) charges
•
•
e is the charge of an electron
d is the distance between the atoms
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IONIC Forces of Attraction
• The electrostatic forces that hold cations and anions together
in an extended array (a lattice) are STRONG!
• As a result of these strong attractive forces, ALL ionic
compounds are solids at room temperature. (Ionic Compounds
have high melting points.)
• Solid ionic compounds DO NOT conduct electricity.
• In the molten state ionic compounds DO conduct electricity.
• Water solutions containing dissolved ionic compounds DO
conduct electricity.
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Formation of a Covalent Bond Between Two
Hydrogen Atoms
Covalent bonds form when elements share
electrons, which usually occurs between
nonmetals.
The basic units formed are molecules.
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Representing Molecular Compounds
•
Molecule: smallest identifiable unit of a pure
COVALENT (not ionic) compound.
Molecules are primarily formed from the nonmetal
elements.
Molecular compounds can be gases, liquids or solids at
room temperature and pressure.
•
There are various ways to represent molecules
structurally:
Structural formulas show the order in which atoms
are bonded.
Perspective drawings show the three-dimensional
arrangement of atoms.
Condensed formulas (condensed structural) group
atoms that are bonded together.
Example: Ethylene Glycol (see slide 2)
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Polyatomic Ions:
• Polyatomic ions consist of more than
one atom.
• Polyatomic ions are usually groups of
NONMETAL elements covalently
bonded together. This group as a
whole has a net charge (+ or –).
Crystal
structure of
calcite
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Chemical Nomenclature: Names and Formulas
•
•
Inorganic Compounds: The naming of ionic and molecular inorganic
compounds will be covered during a LAB period. This should be
review for you! You are expected to be proficient in inorganic
nomenclature. This is essential for success in some future
topics covered in general chemistry!
Some simple Organic (carbon based) Compounds:
Hydrocarbons are compounds that contain only carbon and hydrogen.
Alkanes: simplest type of hydrocarbon, all bonds are single
Alkanes are named using a root name followed by the suffix –ane.
Alcohols: contain the –OH functional* group, covalently bonded
to a carbon atom
Alcohols are named using a root name followed by the suffix –ol.
Carboxylic acids: contain the –COOH functional group
*Functional Group: An atom or group of atoms that imparts characteristic
properties to an organic compound.
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Formula Mass and Molecular Mass
Formula mass:
Sum of atomic masses in amu for ionic compounds and elements.
This is the mass of a single formula unit.
– Example: determine the formula mass of aluminum oxide.
Molecular mass:
Sum of atomic masses in amu for molecular compounds.
This is the mass of a single molecule.
– Example: determine the molecular mass of methanol. Convert this mass to grams.
Note: Formula weight or molecular weight are often used in place of mass. In fact, mass is
“more correct”!
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Stoichiometry
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Questions and Problems
Do the following drawing represent neutral atoms or an ions?
Write the complete chemical symbol including mass number, atomic
number, and net charge (if any).
Which of the following diagrams is most likely to represent an ionic
compound, and which a molecular one? Explain your choice.
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Questions and Problems
Write the chemical formula for the following compound. Is the compound
ionic or molecular? Name the compound.
Which two of the following are isotopes of the same element:
12
6
X
14
6
X
14
7
X
What is the identity of the element whose isotopes you have
selected?
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Questions and Problems
Fill in the gaps in the following table:
Using the periodic table to guide you, predict the chemical
formula and name of the compound formed by the following
elements:
(a) Ga and F
(b) Li and H
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Questions and Problems
A cube of gold that is 1.00 cm on a side has a mass of 19.3 g. A single gold
atom has a mass of 197.0 amu.
(a) How many gold atoms are in the cube?
(b) From the information given, estimate the diameter in Å of a single
gold atom. (0.01 Å = 10-12 m)
(c) What assumptions did you make in arriving at your answer for
part (b)?
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Questions and Problems
There are two different isotopes of bromine atoms. Under normal
conditions, elemental bromine consists of two atoms (a diatomic molecule)
and the mass of a Br2 molecule is the sum of the masses of the two atoms
in the molecule. The mass spectrum of Br2 consists of three peaks:
Mass (amu)
Relative Peak Size
157.836
0.2569
159.834
0.4999
161.832
0.2431
(a) What is the origin of each peak (of what isotopes does each
consist)?
(b) What is the mass of each isotope?
(c) Determine the average molecular mass of a Br2 molecule.
(d) Determine the average atomic mass of a bromine atom.
(e) Calculate the abundances of the two isotopes.
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Questions and Problems
TNT (trinitrotoluene; below) is used as an explosive in construction.
Calculate the mass in grams of carbon in 1.00 lb of TNT.
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