Overview of Notes
Emphasis on Ionic and
The Periodic Table of Elements
In1869, Russian chemist Mendeleev
proposed that elements had a
“periodicity of properties.”
Mendeleev originally tried to organize
elements by atomic weight alone
believing that elements would gradually
and systematically change as weight
Mendeleev actually found that his theory
was only true to an extent.
Physical and chemical properties would
change gradually then suddenly at
These steps came to be referred to as
Elements in the same group
have the same number of
Mendeleev and the Table
The Rows on the Periodic Table are
referred to as the periods.
The columns are referred to as groups.
Elements change gradually along the
period and make more significant
changes between groups.
Elements in groups share many similar
chemical and physical properties.
The Periodic Table of Elements
In Conclusion (Mendeleev)
Mendeleev ascertains that the “periodic”
nature of chemical properties is related to
The way that electrons are around the
nucleus affect the properties.
Bohr’s theory tells us that electrons are not
Electrons are actually arranged in a very
specific pattern called electron shells.
Each electron shell has a limited capacity.
The formula for determining the number
of electrons in a shell is 2n2 where n refers
to the number of the electron shell.
There is a specific way to draw
electron dot diagrams.
The further the electron shell is away from
the nucleus, the larger its capacity.
Valence electrons refer to electrons found
in the outermost shell regardless of the
total number of electron shells.
The row or period number that an
element resides in on the table is equal to
the number of shells that contain
Ionic compounds are composed of
charged ions that are held together by
In an ionic bond, one element will give up
an electron to another element to create
the ideal number of valence electrons for
the outer shell.
Almost all ionic compounds are made up
of a metal with a non-metal.
Characteristics of Ionic
Binary Compounds are made up of two
elements composed of a metallic positive
ion (cations) and non-metal negative ions
Ternary Compounds contain three
elements composed of a monoatomic
ion and a polyatomic ion.
For the purpose of this class we will mainly
focus on Binary Compounds.
Important Note about Ionic
Ionic Compounds do not show
how the compound actually
exists in nature. It shows the ratio
by which the ions combine.
For Example: Calcium Chloride
(CaCl2) does not mean that
there is one calcium atom and 2
This does mean that there will be
twice as many chlorine atoms as
Molecular Compounds are created by
In this type of bond, electron pairs are
shared between elements.
Covalent bonds are usually not good
conductors of electricity and will have a
lower melting and boiling point.
Whether or not a compound is made up
of ions, each atom in the compound will
have an apparent charge.
This charge is referred to as the oxidation
This number represents the charge that an
atom would have if electrons were
transferred completely to the atom with
the greater attraction.
Oxidation numbers are used to predict
the rates by which atoms will combine
when they form compounds.
Oxidation numbers are written as
superscripts in chemical formulas.
Table 5-2a - Predicting Oxidation Numbers
1. In free elements (that is, in uncombined state), each atom has an oxidation number of zero. Ex. In O2, the
oxidation number of each oxygen atom is zero.
2. For ions composed of only one atom, the oxidation number is equal to the charge on the ion. Ex. The
oxidation number of Ca2+ is +2.
3. All alkali metals (elements in column 1of the periodic table, with the exception of hydrogen) have an
oxidation number of +1. Ex. The oxidation numbers of Li, K, and Na will always be +1.
4. All alkaline earth metals (elements in column 2 of the periodic table) have an oxidation number of +2. Ex.
The oxidation number of Ba is +2.
5. The oxidation number of Aluminum (Al) is always +3.
6. The oxidation number of oxygen in most compounds (such as H2O and CO2) is -2. In hydrogen peroxide
(H2O2) and peroxide (O22-) oxygen shows a -1 oxidation number.
7. The oxidation number of hydrogen is +1, except when in is bonded to a metal as a negative ion, in which
case it is -1. Ex. H2O shows hydrogen as +1. NaH shows hydrogen as -1.
8. When halogens (elements in column 17 on the periodic table) form negative ions, they will have an
oxidation number of -1. Ex. NaCl and CaCl2 both show chlorine with a -1 oxidation number.
9. In a neutral molecule, the sum of the oxidation numbers of all of the atoms must be zero. Ex. In H2O, each
hydrogen is +1 and the oxygen is -2. So, (2 x +1) + (-2) = 0.
10. In a polyatomic ion, the sum of oxidation numbers of all the elements in the ion must be equal to the net
charge of the ion. Ex. In the polyatomic ion known as hydroxide (OH-), the oxygen is -2 and the hydrogen is
+1. So, (-2) + (+1) = -1, the same as the charge on the hydroxide ion (OH-)