http://www.ck12.org Chapter 6. Periodic Table
FIGURE 6.3
The modern periodic table of the elements is a lot like Mendeleev’s table. But the modern table is based on
atomic number instead of atomic mass. It also has more than 110 elements. Mendeleev’s table only had about
65 elements.are the elements starting with lanthanum (La) in period 6 and actinium (Ac) in period 7. Some elements in period 7
have not yet been named. They are represented by temporary symbols, such as Uub.
Groups
Columns of the modern table are called groups, as they are in Mendeleev’s table. However, the modern table has
many more groups —18 to be exact. Elements in the same group have similar properties. For example, all elements
in group 18 are colorless, odorless gases. You can read about the different groups of elements in this chapter’s lesson
on "Groups of Elements."
Lesson Summary
- Mendeleev developed the first periodic table of the elements in 1869. He organized the elements by increasing
atomic mass. He used his table to predict unknown elements. These were later discovered. - The modern periodic table is based on atomic number. Elements in each period go from metals on the left to