What energy is required to move from ca+ca+ to ca2+ca2+ + e−e−?

Second Ionization energy

Explanation:

Let us write the reaction equation properly:

                  Ca⁺ → Ca²⁺ + e⁻

In the reaction above, we see that calcium goes from a single charge to being doubly charged by losing an electron.

Different atoms binds their valence electrons with different amount of energy. We must supply enough energy to remove the most losely held electrons in an atom. This amount of energy required is called the ionization energy.

The first ionization energy removes the outermost electron and makes the atom to become an ion.

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