1. Organizing the Elements

2. Mendeleev’s Periodic Table
Mendeleev arranged the elements into rows in order of increasing mass so that elements with similar properties were in the same column.

3. Periodic Table
The periodic table is an arrangement of elements in columns, based on a set of properties that repeat from row to row.
Within a column, the masses increase from top to bottom.

4. Periodic Table
The close match between Mendeleev’s predictions and the actual properties of new elements showed how useful his periodic table could be.
With the periodic table, chemists could do more than predict the properties of new elements. They could explain the chemical behavior of different groups of elements.

5. The Periodic Law
Mendeleev developed his periodic table before the discovery of protons.
In the modern periodic table, elements are arranged by increasing atomic number (number of protons).

6. Periods Each row in the table of elements is a period.
Period 1 has 2 elements.
Periods 2 and 3 have 8 elements, etc.

7. Groups Each column on the periodic table is called a group.
Properties of elements repeat in a predictable way when atomic numbers are used to arrange elements into groups.

8. Periodic Law
The elements in a groups have similar electron configurations.
An element’s electron configuration determines its chemical properties.
Members of a group in the periodic table have similar chemical properties.
This pattern of repeating properties is the periodic law.