How would you write the equation of the electron affinity of S-?

An atom's affinity for electrons is called its electron affinity; it is the propensity to pick up an electron.

Electron affinity is commonly written as positive because, from the atom's point of view, it absorbs energy from the electron in order to absorb it into itself; conversely, when the electron is absorbed more readily, the electron affinity is less positively written.

You would write a reaction that therefore involves the absorption of an electron into the atom and the release of energy from the electron. The kinetic energy of the electron is released when energy is absorbed from the electron as potential energy.

Ionization energy, on the other hand, is the propensity to lose an electron.

Ionization energy is commonly written as negative because, from the atom's point of view, it provides energy to the electron during its release from the atom; conversely, when the electron is released with greater ease, the ionization energy is less negative.

You would write a reaction that thus entails the release of an electron from the atom and the absorption of energy into the atom. Potential energy is stored in the atom when energy is released from the electron as kinetic energy.

The equation for the electron affinity of S^- (sulfide ion) is:

S + e^- -> S^-