This causes the electron to move closer to the nucleus, thus increasing the electron affinity from left to right across a period. Moving from left to right across a period, atoms become smaller as the forces of attraction become stronger.
With a larger distance between the negatively-charged electron and the positively-charged nucleus, the force of attraction is relatively weaker. This means that an added electron is further away from the atom's nucleus compared with its position in the smaller atom. \( \newcommand\): Periodic Table showing Electron Affinity TrendĮlectron affinity generally decreases down a group of elements because each atom is larger than the atom above it (this is the atomic radius trend, discussed below).
