# Chemistry Help: Which of the following species has the greatest number of electrons?

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

• 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