What is the ground state of an atom

"a ground-state atom is an atom in which the total energy of the electrons can not be lowered by transferring one or more electrons to different orbitals."

since the atomic number is the number of protons in the nucleus, as we move to the left on the periodic table, the electrostatic pull between the nucleus and the valence electron shell decreases. as we move down a group (vertical column), the valence shell energy level gets further and further from the nucleus.