Groups in the periodic table contain elements with the same number of electrons in their outermost shell, giving them similar chemical properties. Periods contain elements with the same number of electron energy levels. The periodic table arranges the 118 known elements and provides information about their properties based on their position and relationships between protons, neutrons, and electrons.

1. GROUPS AND
PERIODS -Columns in the periodic table represents “groups”
-There are 18 groups in the periodic table.
-Elements of the same the same group have the same chemical
properties as the all have the same number of electron/s in the
outer most energy levels.

2. -Rows in the periodic table represent “periods”.
-There are 7 periods in the periodic table .
-Elements of the same period have the same number of
energy levels

3. The Periodic Table of Elements

4. Periodic Table
A great deal of information about an element can be
gathered from its position on the period table.
Understanding the organization and plan of the periodic table
will help you obtain basic information about each of the 118
known elements.

5. MASS NUMBER
Atomic Mass (Mass Number) is the
number …………….
__________
Atom p+ n0 e- Mass #
___ ___ ___ ___
Oxygen - 8
______ - ___ 33 42
___ ___
______ - 31 15
___ ___ ___

6. RECALL - HOW ARE P, N, E-RELATED?
atomic number = # protons
# protons = …………….
# protons + # neutrons = atomic mass
# neutrons = …………….
…………….

7. How many protons, neutrons and electrons are found in an
atom of Cs?
_____________
 …………….
…………….
Therefore, # Neutrons = …………….
_____________
_____________
55
Cs
133
EXAMPLE 1

8. 11
Na
Sodium
23
___________
___________
___________

9. Example 2
 If an element :Magnesium
a) number of protons
b) number of neutrons
c) number of electrons
d) complete symbol
=_____________
= _____________
= _____________
_____________