1. The Atomic Number

* The key: The atomic number of an element tells you the number of protons in its nucleus.

* Why it works: In a neutral atom, the number of protons (positive charge) is equal to the number of electrons (negative charge).

Example:

* Oxygen has an atomic number of 8. This means a neutral oxygen atom has 8 protons and 8 electrons.

2. Ions

* Ions are atoms that have gained or lost electrons.

* Positive ions (cations) have lost electrons, so their number of electrons is less than their atomic number.

* Negative ions (anions) have gained electrons, so their number of electrons is more than their atomic number.

Example:

* A calcium ion (Ca²⁺) has lost 2 electrons. Calcium's atomic number is 20, so a calcium ion has 18 electrons.

Here's a quick summary:

* Neutral Atom: Number of electrons = Atomic Number

* Cation: Number of electrons = Atomic Number - (number of positive charges)

* Anion: Number of electrons = Atomic Number + (number of negative charges)

Let me know if you have any specific elements or ions you want to find the electron count for!