How many elements are possible in the first period?

The symbol of an element is $Une$. Its atomic number is

The elements with atomic numbers $Z=117$ and $Z=120$ have not yet been discovered. In which family or group would you place these elements,and what would be their expected electronic configuration?

Provide the name,symbol,and atomic number of the first and last elements for each period from $1$ to $7$ of the periodic table.

The cause of periodicity of properties is

What is the main basis for the arrangement of elements in the modern periodic table? Describe it.