The row of the periodic table which contains hydrogen and helium has only two elements, while the next row has eight. Why is that so?

What fundamental property determines the element to which a particular atom belongs?

What quantum numbers are necessary to build up the periodic table?

Which of the quantum numbers has the most influence on the row of the periodic table in which an element belongs?

Describe the role of the Pauli exclusion principle in the buildup of the periodic table.