Question

Question #89d4c

Answer 1

`["Ne"]`

Explanation:

Start by looking for calcium, `"Ca"`, in the Periodic Table. You will find that this element is located in period `4`, group `2` and that it has an atomic number equal to `20`.

This tells you that an atom of calcium contains `20` protons inside the nucleus and `20` electrons surrounding the nucleus.

You can thus say that the electron configuration of an atom of calcium must account for a total of `20` electrons.

As you know, you can use the Aufbau Principle to write the full electron configuration for an atom of calcium.

You will end up with

`"Ca: " 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2`

Now, when calcium loses two electrons, it becomes a cation with an overall `2+` charge. These two electrons will be removed from the fourth energy level, the valence shell of an atom of calcium. More specifically, these two electrons will come from the `42` orbital.

`"Ca: " 1s^2 2s^2 2p^6 3s^2 3p^6 color(red)(cancel(color(black)(4s^2)))`

This implies that the full electron configuration of a calcium action will look like this

`"Ca"^(2+): 1s^2 2s^2 2p^6 3s^2 3p^6`

Finally, to write the abbreviated electron configuration of a calcium cation, you need to look in the Periodic Table for the noble gas that comes immediately before calcium.

This noble gas is neon, `"Ne"`. The full electron configuration of an atom of neon looks like this

`"Ne: " 1s^2 2s^2 2p^6 3s^2 3p^6`

Notice that this is the same electron configuration as the one you have for the calcium cation. To show this, you can write

`"Ca"^(2+): ["Ne"] ->` the nogle gas shorthand of a calcium cation

Here `["Ne"]` simply means the full electron configuration of neon.

Notice that you can write the noble gas shorthand of an atom of calcium like this

`"Ca: " ["Ne"] 4s^2`

Once again, the `["Ne"]` simply means the electron configuration of neon, the noble gas that comes immediately before calcium in the Periodic Table.