Which of the following species has the greatest
number of electrons?
1. Al+
2. Si2+
3. Na+
4. Mg−
5. Mg
6. Al2+
7. Na−
8. P3+
Can you please explain how you got the answer? I never really understood this in class.
Thank you! <3
2 Answers

The general formula for this problem is
Atomic number – the charge = the number of electrons.
Al Atomic number = 13
Al – 1 = the number of electrons.
13 – 1 = 12 So this species has 12 electrons left.
Si = 14
Si – 2 = number of electrons.
14 – 2 = 12
Magnesium = 12
12 – (1) = 13
Note: Mg would be hard pressed to take on an electron. Also note how the extra electron contributes a second minus sign. That’s because an electron is minus and the formula asks us to use a minus.
Mg [no charge]
Mg – 0 = number of electrons.
12 – 0 = 12
I’ll let you do the rest of them. Just use the formula.

The element’s periodic table number represents the number of Electrons the atom has originally. If it is positively charged then it has that many less electrons and if its negatively charged it has that many more electrons so
Al normally has 13
Al+ has 12
Si normally has 14
Si2+ has 12
Na normally has 11
Na+ has 10
Mg has 12
Mg has 13
Al2+ has 11
Na has 12
P normally has 15
P3+ has 12
So Mg has the greatest number of electrons
Source(s): 3 Years of Chemistry