Question

How many electrons has an atom with atomic number 12?

Answer 1

Well, if it is a neutral atom, we gots 12 electrons....

Explanation:

`Z`, `"the atomic number"`, specifies the number of protons, positively charged nuclear particles, and also if `Z=12`, then we know that the element is magnesium... How do we know this? Because as chemists we have access to a Periodic Table.

But if we specify a neutral atom, there MUST be equal numbers of positive charges, nuclear protons, and negative charges, electrons, that are conceived to orbit around the nucelar core.

Magnesium commonly forms the `Mg^(2+)` ion....how many electrons does this beast have?

Answer 2

Well, it depends.

Explanation:

Usually, we are going to talk about neutral atoms, so the number of electrons and protons will be the same. In this case, a neutral atom with `12` protons will have `12` electrons.

On the periodic table, the atom with `12` protons is magnesium, which is in group `2`.

Therefore, it will most likely lose `2` electrons to have `10` electrons, and form a noble gas configuration. So, magnesium becomes `Mg^(2+)`.

But usually, we just say that the proton number is equal to the electron number, unless we talk about ions.