## Chemistry: The Central Science (13th Edition)

The half arrows in an orbital diagram represent the electrons in a single orbital. Each half arrow represents one electron, with the direction of the half arrow standing for electron spin. It is agreed that the half arrow heading up represents an electron with $m_s=+\frac{1}{2}$ (positive spin quantum number), while the half arrow heading down represents an electron $m_s=-\frac{1}{2}$ (negative spin quantum number).