1. The Periodic Table of Elements

2. Who Designed the Periodic Table
Russian chemist Dimitri Mendeleev (late 1800’s)
Originally arranged
by increasing atomic
mass
Later arranged by
increasing atomic #
(Henry G.J. Moseley)

3. Columns in the Periodic Table
Known as Groups or Families
A group or family has similar but not identical properties
Example: Group 1 or Alkali Metals
Properties – soft, white, shiny metals, highly reactive

4. Rows in the Periodic Table
Known as Periods
Are not alike in properties
However there is a pattern
The first element in a period is almost always an active solid
The last element is an inert or inactive gas
Each Period tells you how many energy levels each atom has
Each energy level can hold a certain number of electrons
Energy level electrons
Energy level electrons
Energy level electrons
Energy level electrons
Energy level electrons
Energy level electrons
Energy level electrons

5. Why do we care about how many electrons an atom has?
The reactivity of an element is due to its electrons specifically the valence electrons
Valence electrons are the electrons found in the outer shell of an atom.
Orbit or Shell
Nucleus
Valence Electrons

6. Lewis Dot Diagrams
A diagram to represent electrons in the outer energy level of an atom
Uses the atomic symbol and dots
Example: Hydrogen H•
Beryllium Be:
Carbon : C :

7. Trick to the Lewis Dot Diagrams
Some atoms are very easy to figure out how many electrons are in the valence shell
Group 1 has 1
Group 2 has 2
Group 13 has 3
Group 14 has 4
Group 15 has 5
Group 16 has 6
Group 17 has 7
Group 18 has 8
Groups 3-12 the number varies