# GRE question - atomic physics

## Homework Statement

The ground state electron configuration for phosphorus, which has 15 electrons, is

• 1s^2 2s^2 2p^6 3s^1 3p^4
• 1s^2 2s^2 2p^6 3s^2 3p^3
• 1s^2 2s^2 2p^6 3s^2 3d^3
• 1s^2 2s^2 2p^6 3s^1 3d^4
• 1s^2 2s^2 2p^6 3p^2 3d^3

## The Attempt at a Solution

No clue.

Gokul43201
Staff Emeritus
Gold Member
We can not help you unless you show us some effort/thought/ideas...anything! What have you tried so far?

We can not help you unless you show us some effort/thought/ideas...anything! What have you tried so far?

I've tried looking up to see what all those numbers mean, but I couldn't find any info. It's not in the physics book I have (Ohanian).

tbh, you could probably work this one out with almost no physics/chemistry knowledge. If you looked at it as a sequence, (provided you know what the groundstate means), you should be able to get it.

tbh, you could probably work this one out with almost no physics/chemistry knowledge. If you looked at it as a sequence, (provided you know what the groundstate means), you should be able to get it.

You would at least have to now what sublevels "s", "p", "d" and "f" are. And you'd have to now the number of orbitals and the maximum number of electrons each can have.

Gokul43201
Staff Emeritus
Gold Member
Bill, that's correct. If you still have trouble with this look up the Aufbau Principle.

dynamicsolo
Homework Helper
Bill, that's correct. If you still have trouble with this look up the Aufbau Principle.

Fortunately, he was only asked to find the configuration for phosphorus. Aufbau only gets you so much mileage -- the simple picture starts to break down when the atomic number gets to the mid-20s (the iron group elements)...