When is the process exothermic and when is it endothermic? [closed]

When electrons are being added/removed from atoms or ions how can I tell if the process is exothermic or endothermic? For example in the question below, how could I tell for sure which of the processes are exothermic and which are endothermic?

$$\ce{Ca -> Ca+ + e–}$$

$$\ce{I + e– -> I–}$$

$$\ce{O– + e– -> O^{2–}}$$