Here's why:

* Valence electrons are the key: You are correct in focusing on valence electrons. These are the outermost electrons, and they are the ones involved in chemical bonding.

* Positive ions lose electrons: A positive ion is formed when an atom *loses* one or more electrons.

* The charge tells you how many electrons are lost: The charge of the positive ion directly indicates the number of electrons lost. For example, a +2 charge means the atom lost 2 electrons.

Therefore, to find the number of electrons available for bonding in a positive ion, you need to:

1. Determine the number of valence electrons in the neutral atom.

2. Subtract the number of electrons lost, which is equal to the magnitude of the positive charge.

Example:

Let's take the example of a magnesium ion (Mg²⁺):

1. Magnesium (Mg) has 2 valence electrons.

2. Mg²⁺ has a +2 charge, meaning it lost 2 electrons.

3. Therefore, Mg²⁺ has 0 valence electrons available for bonding.

Important Note: While a positive ion has fewer valence electrons than its neutral atom, it is still capable of forming bonds. This is because it can form ionic bonds by attracting negatively charged ions.

In summary, the number of electrons available for bonding in a positive ion is found by subtracting the magnitude of the positive charge from the number of valence electrons in the neutral atom.