Which of these periods contain elements with electrons s, p,d and f orbitals? periods 1-3 periods 1-4
periods 3-5
periods 6-7

All the elements are arranged by melting points on the periodic table. in row they go from metals to gasses. in the row from sodium to argon, sodium is more reactive than the one on its right, magnesium.

Answerhund's rule;