Question

By the early 20th century protons and electrons had been discovered.
Describe how knowledge of the numbers of protons and electrons in atoms
allow chemists to place elements in their correct order and correct group.​

Answer 1

Answer:

The modern periodic table lists the elements in order of increasing atomic number (the number of protons in the nucleus of an atom). ... This was mainly because the idea of atoms being made up of smaller sub-atomic particles (protons, neutrons and electrons) had not been developed.