Nomenclature
Writing and Naming Chemical Compounds
What’s a Compound?
NOTES 1: Compounds and Their Formulas
• Compounds have been defined as matter formed by two or more
different elements joined by a chemical bond.
• Formulas allow scientists to identify the composition of compounds. Every
formula contains the symbols of elements that make up the compound.
One example is NaCl, also known as table salt, is formed when sodium (Na)
and chlorine (Cl) combine in a chemical reaction.
NaCl
What does a formula “tell” you?
Baking soda, or sodium bicarbonate, has a more complicated formula, NaHCO3.
Baking soda is formed when sodium (Na), hydrogen (H), carbon (C), and
oxygen (O) combine in a chemical reaction. The small number 3 in the formula is
called a subscript.
A subscript shows the number of atoms of an element in a compound.
The subscript always refers to the symbol just before it in the formula.
If there is no subscript following a symbol, it means there is only one of that
kind of atom in the molecule.
Example: Baking soda thus contains, ____________ atom of sodium, _____
atom of hydrogen, _____ atom of carbon, and ______ atoms of oxygen in
each molecule.
A molecule is the term used for any bonded elements.
NaHCO3
Identify the following substances:
oxygen
oxygen
Carbon
monixide
Ammonia
Carbon
dioxide
NOTES 2: VALENCE ELECTRONS,
LEWIS DOT DIAGRAMS, AND
OXIDATION NUMBERS
Review: Bohr’s Electron
Model
1. How many total electrons are in a
neutral atom of Sulfur?
2. How many electrons are in
sulfur’s highest energy level (it’s
most outer shell)(HINT: use the
picture to the right)?
3. How many electrons does sulfur need to gain
or lose in order to have 8 valence electrons
(electrons in the outermost shell)?
Recap: Bohr’s Electron Model
Bohr developed an atomic model
in which the electrons are
arranged in specific energy
levels.
The lowest level (n=1) is located
closest to the nucleus. The highest
level is located farther away from
the nucleus.
Recap: Bohr’s Electron Model
*The electrons in the highest
energy level for any element are
known as valence electrons.*
Valence electrons are involved in
chemical bonding.
Bonding and Valence Electrons
Video Clip
Valence Electrons:
Valence Electrons can be easily found by
looking at the Group number or “A”
number located above the column where
the element is located on the periodic
table.
Examples:
2
2 so it has ___
2 and ____A
Mg= Group # ___
valence electrons.
4
Pb= Group # 14
___ and ____
4 A so it has ____
valence electrons.
Valence Electrons the Quick and Easy Way
Determine the number of valence electrons.
Phosphorus
Argon
Lead
Barium
5 valence electrons
8 valence electrons
4 valence electrons
2 valence electrons
Exceptions
• * This ONLY works for Group A Elements
(the Representative Elements)
• Helium  two valence electrons
Label the Valence Electrons for each Column on the Periodic Table
Label the Valence Electrons for each Column on the Periodic Table
LEWIS DOT DIAGRAMS: is a diagram in
which the chemical symbol of an element
represents the nucleus and the inner energy
level and “dots” represent the valence
electrons.
There can only be up to 8 valence electrons and
thus only 8 dots around a symbol. The first 4 dots
are single and then they pair up as more are
added. Octet rule states that all atoms wish to
be like the Nobel gases (group 18) with a full
valence of 8 electrons.
Lewis Dot Diagrams
Element
Symbol
One Dot for
Each Valence
Electron
How Are the Dots Arranged?
1
8
4
5
X
7
3
2
6
Example Dot Diagrams
Draw the dot diagrams for each of
the following elements.
•Helium
He
•Carbon
C
F
•Neon
Ne
Oxidation numbers
OXIDATION NUMBERS: is the number of electrons an
atom gains, loses, or shares when it
forms a chemical bond and achieves the octet rule.
This will also be the charge of the ION.
Metals as a rule lose electrons and will have a (+) charge.
Nonmetals will gain electrons and have a ( -) charge
Nobel gases in group 18 will not
lose or gain and have a 0 charge
Label the periodic table for the ion
charge created as atoms achieve the
Octet rule (full valence of 8):
4
0
0
4
+-4
-1
7
8
0
0
Complete homework
page 6