How does the modern periodic table of the elements differ form mendeleyev's chart?

The Period Table of Elements has more elements that have been discovered since Mendeleyev's time.

In the modern table the elements are arranged with increasing atomic number. In Mendeleyev's table, they were arranged with increasing atomic weight.

2h2o2--> 2h2o + o2

this reaction is of the spontaneous decomposition of hydrogen peroxide down into water and oxygen.

add 2 molecules of hydrogen peroxide and 2 molecules of water. since oxygen is naturally diatomic, the total number of atoms of each element is now the same on both sides of the equation so it is balanced.

this may not be entirely correct but let me know.