The electron configuration for an element is 1s2 2s2 2p6 3s2 3p6. What is the atomic number of the element? * A. 3
B. 11
C. 18
D. 22

answer: atomic mass was originally used to arrange elements on the periodic table, but is no longer used to organize the modern version.

explanation:

originally atomic mass was used to arrange elements on the periodic table from left to right in a row. each column then shows similar properties of elements of a group.

in modern periodic table, the atoms are arranged in increasing atomic number. as atomic number represents the number of protons in an atom which is unique for every atom.