Atomic and Molecular Orbitals
The horizontal rows of the periodic table are called Periods.
Each period represents a different quantum energy level.
All of the atoms in a given row have a set of electrons at various energy levels (i.e. the principle quantum level; 1, 2, 3 etc.)
The highest energy level is called the valence shell.
Within each period there may be 1, 2, 3 or 4 sublevels, designated as s, p, d, and f. These are atomic orbitals.
Recall the following principles from General Chemistry