Transcript Chapter Two Chemical Names and Formulas ' *Introduction to Chemical Bonding* ' • Every substance is either an element or a compound • A Compound.

Chapter Two
Chemical Names and Formulas
' *Introduction to Chemical Bonding* '
• Every substance is either an element or a
compound
• A Compound consists of more than one kind of
atom
• A compound is either molecular or ionic in nature
Characteristics of Molecular and Ionic Compounds:
Characteristic
Molecular Compound
Ionic
Compound
Representative Unit Molecule
Formula Unit
Type of Elements
Nonmetallic
Metal/Nonmetal
Physical State
Solid, Liquid, Gas
Solid
Melting Point
Low(usually < 300 oC)
High(>300 oC)
Molecules and Molecular
Compound
• Molecule- the smallest electrically neutral unit of a
substance that still has the same properties of that
substance
• Molecular compound- Atoms of different elements can
combine chemically to form compounds
• Atoms combine to form molecules
• Compounds are composed of molecules
Representing Chemical
Compounds
• Molecular compounds are composed of two or more
nonmetals
• A molecular formula shows the number and kinds of atoms
present in a molecule of a compound
• Ionic Compounds are composed of oppositely charged ions
combined in electrically neutral groupings
• A formula unit gives the lowest whole
number ratio of ions in the compound.
Periodic Table Facts
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The # of the A Group = # of outer electrons
That is (1A,2A,3A-8A) OR (IUPAC 1,2,13-18)
Elements that: Lose electrons are positive
Elements that: Gain electrons are negative
Elements are most stable when they have 8 outer
electrons—known as the Octet Rule
Example: Chlorine has 7 electrons/ gains 1/has a
negative 1 oxidation number Cl is in Group 7A
Losing/Gaining Electrons
• Atoms that have 1, 2 or 3 electrons in their outer
levels will tend to lose them in interactions with
atoms that have 5, 6 or 7 electrons in their outer
levels. Atoms that have 5, 6 or 7 electrons in their
outer levels will tend to gain electrons from atoms
with 1, 2 or 3 electrons in their outer levels. Atoms
that have 4 electrons in the outer most energy
level will tend neither to totally lose nor totally
gain electrons during interactions.
b Ionic Charges a
• The charges of the ions of the representative
elements can be determined by the position of
these elements in the periodic table
• Most transition metals have more than one
common ionic charge
• A polyatomic ion is a group of atoms that behaves
as a unit and has a charge
+
-
• Binary (two-element) ionic compounds are named
by writing the name of the cation followed by the
name of the anion.
• When a cation can have more than one ionic
charge, a Roman numeral is used in the name.
• Ternary ionic compounds contain at least one
polyatomic ion.
Criss-Cross Method
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Criss-Cross: write symbols
put oxidation # above each symbol
criss-cross # (not charge)
reduce #’s to get lowest possible ratio
do not need to write the # 1
A Group Oxidation # Short-cut
• 1A 2A 3A 4A 5A 6A 7A
• +1 +2 +3 +4 -3 -2 -1
2 EXAMPLES OF IONIC COMPOUNDS:
• Zinc sulfide
• ZnS
• Aluminum Chloride • AlCl3
• Barium Nitride
• Ba3N2
• Copper (II) bromide • CuBr2
Ternary Ionic Compounds
• Use the criss-cross method
• Polyatomic ions are involved… “many atoms”
that act together with a single charge
• “treat” the polyatomic as if it is a single element
regarding the criss-cross…you cannot change the
subscripts for the polyatomic.
• You might need to use parentheses when crisscrossing oxidation numbers
Ternary Ionic Compounds
• Sodium Hydroxide…..NaOH
• Calcium Nitrite……...Ca(NO2)2
• Magnesium Sulfate…..MgSO4
• Ammonium Nitrate…..NH4NO3
• Calcium Phosphate…..Ca3(PO4)2
Molecular Compounds
• Binary molecular compounds are composed
of two nonmetallic elements.
• Prefixes are used to show how many atoms
of each element are present in a molecule of
the compound.
• DO NOT need to criss-cross for molecular
compounds…Reason: prefix given
Summary of Naming and
Formula Writing
Prefixes Used in Naming Binary Molecular Compounds
Prefix
#
Prefix
#
Mono
1
Hexa
6
Di
2
Hepta
7
Tri
3
Octa
8
Tetra
4
Nona
9
Penta
5
Deca
10
Examples:
Name these binary molecular
compounds:
Answers:
1. OF2
2. SO3
1.
2.
oxygen difluoride
sulfur trioxide
Write formulas for the
following binary molecular
compounds:
3. Nitrogen trifluoride
4. Dinitrogen tetroxide
3. NF3
4. N2O4