Final answer:
Adding electrons to an atom increases its size, decreases ionization energy, and decreases electron affinity due to changes in electrostatic interactions within the atom.
Step-by-step explanation:
The addition of one or more electrons to an atom will increase the size of the atom, decrease the ionization energy, and decrease the electron affinity. This is because the electrostatic attraction between the nucleus and the electron cloud adjusts when electrons are added. Anions, which are atoms that have gained electrons, tend to be larger than the parent atom due to the increased electron-electron repulsion in the valence shell while the nuclear charge remains constant.
Ionization energy, associated with the removal of an electron to form a cation, decreases with the addition of electrons, as the outer electrons are further from the nucleus and thus require less energy to remove. Electron affinity generally decreases with the growth in atomic size since electrons added to a larger atom experience a lesser attractive force from the nucleus.