Question

according to atomic structure,what determines which element will be the first and last in the periodic table

Answer 1

Many periodic properties are there like :-

1) Ionisation potential
2) Electron affinity
3) Electronegativity
4) Melting and boiling point
5) Density
6) Atomic size

Answer 2

The main reason is just it's Atomic Number , as we always want study a periodic table in a well mannered way therefore they are arranged in a orders .
Properties only determine in which group or period it should be taken but 1st and last element are only on the basis of Atomic number.