What is the 250 green numbers on the side

1, 2, 3, ..., 250

Explanation:

Whatever you mean.

The number of electrons in an atom is directly proportional to the number of protons, which is clearly represented by atomic number.

If you were to notate all of the electron configurations of the atoms in the 2nd row, you would clearly see an increase in the number of valence electrons from left to right.