What has the higher first ionization energy? Mg or Cl

Ionization Trend: First ionization energy will increase left to right across a period and increase bottom to top of a family (column).

If we compare Mg and Cl:

Mg is column 2 (far left) in the periodic table, while Cl is column 17 (far right). Based on the ionization rule explained above, Cl will have the higher first ionization energy.

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.