1. How it came to be How it is organized now
The Periodic Table
How it came to be
How it is organized now

2. Dmitri Medeleev (1869)
Put the elements into certain “groups” or “families”
He knew of 64 elements at that time.
Based his organization on chemical properties of the elements.
Saw that these chemical properties increased, therefore knew they had to be in an ascending order. (AKA atomic mass)

3. Dmitri Medeleev (1869)
Mendeleev left blank spaces in his table when the properties of the elements above and below did not seem to match.
Used his table to predict properties of the missing elements, even though they had not been discovered yet.

4. Dmitri Medeleev (1869)

7. Henry Moseley (1901)
Found that the properties of elements were based on their atomic number, rather than atomic mass.
This allowed the gaps in the table to be explained.
Moseley created the modern periodic table, in which each succeeding element has one more proton or electron than the former element.

8. Henry Moseley

9. Modern Periodic Table Periods on the Periodic Table
The horizontal rows
Numbered 1-7
As you move through the periods, there are more electron orbitals. (i.e. Period 1 has 1 electron orbital and Period 7 has 7)
The number of electron orbitals also represents the energy level of an element (how many electrons does it have)

11. Modern Periodic Table Groups on the Periodic Table
The vertical columns.
Old System: Numbered using Roman Numerals I – VIII with an ‘a’ or ‘b’ following it.
Indicates number of valence electrons
New method is to use a numbering system of 1 – 18 from left to right.
Elements in the same group share SIMILAR CHEMICAL PROPERTIES.

13. Periodic Law
When you combine the ideas behind ‘periods’ and ‘groups’ in the Periodic table, you come up with this law:
‘All elements are arranged according to atomic number resulting in a reoccurring pattern of similar properties in different elements. ‘

14. How did Medeleev come up with his ideas???
Time to play cards