Can someone help me with a basic Physical Science Question?

Question

An atom of Iron has 26 electrons. How many are in the outer orbital? Do I subtract 2, and thats the answer. Or, do I go all the way out to the outside orbital?

Answer 1

My guess is that they are asking how many electrons are in the outer shell.  Either way, the best answer is 2.  

I will try to offer a fuller explanation, as you may be asked to account for your answer.

Each shell can hold 2 * n^2 electrons. (n = the number of the shell)

So the first shell holds 2 * 1^2 = 2

The second shell holds 2 * 2^2 = 8

The third shell hold 2 * 3^2 = 18

The shells are arranged into orbitals, each orbital can hold 2 electrons:

1 s orbital :  2 electrons

3 p orbitals: 6 electrons

5 d orbitals: 10 electrons

7 f orbitals: 14 electrons

The first shell only has an "s" orbital, so it can only hold  2 electrons.

The second shell has "s" and "p" orbitals, so it can hold 8 electrons.

The third shell has "s," "p," and "d" orbitals, so it can hold 18 electrons, BUT the 4s orbital will fill up before the 3d orbital starts to fill.

So the third shell gets 8 electrons, then two go into the 4s orbital, and then the 3d orbitals start to fill.

There are 2 electrons in the 4s orbital, and 6 in the 3d subshell.

The maximum that each orbital can hold is 2.  One of the 3d orbitals holds  2 electrons, the others have 1.

Arguably, the 4s orbital is the outermost orbit.  It holds two electrons, and the 4th shell also holds the same two electrons.