Valence electrons are the electrons in the outermost shell of an atom. Here's how to find them for calcium:

1. Find Calcium on the Periodic Table: Calcium (Ca) is in the second column (Group 2) of the periodic table.

2. Determine the Electron Configuration: The electron configuration of calcium is 2, 8, 8, 2. This means it has:

* 2 electrons in the first shell (1s²)

* 8 electrons in the second shell (2s² 2p⁶)

* 8 electrons in the third shell (3s² 3p⁶)

* 2 electrons in the fourth shell (4s²)

3. Identify the Valence Shell: The outermost shell is the fourth shell, which contains the 2 electrons (4s²).

Therefore, the valence electrons of a calcium atom are located in the fourth shell, specifically in the 4s orbital.