4. 1-He Prepared 67 cards one for each element.
2. He wrote the name of the element, atomic mass and its important
properties on cards
3. He arranged the elements in order of increasing atomic mass from the
left to the right side in the horizontal rows "were known later as period
4. He arranged the elements of similar Chemical properties in vertical
columns "were later known as group“
5. The properties of elements were repeated periodically by the beginning
of each new Period.
5. He classified the elements of each main group into two
subgroups (A&B) due to the difference between their properties
.
6. It is the first real Periodic table for classifying elements.
It includes 67 elements.
The elements are classified in an ascending order
according to their atomic mass (weight).
7. Watch this video before the
next the lesson
https://youtu.be/9IvP7CQ-
UBw
