Chemestry electronic structure and periodic table

Electronic structure: 

Electrons always occupy shells. 

The lowest energy levels are always filled first - these are the ones closest to the necleus. 

Only a certain amount of electrons are allowed in each shell.

1st shell - 2 electrons, 2nd shell - 8 electrons etc.

Developement of the periodic table:

early 1800 elements were arranged by atomic mass.

Scientists had no idea of atomic structure or of protons, neautrons or electrons so there was no such thing as atomic number to them.

The only thing that scientists could measure was relatice atomic mass, and so the known elements were arranged via atomic mass.

Early periodic tables were not complete and some elements were placed in the wrong group.

Demitri Mendeleev theory:

Mendeleev over came some of the problems of the early periodic tables by taking 50 of the…