Writing Electronic Configurations

Neutral Ions

-always start with the lowest level first (Aufbau Principle)

-Figure out how many electrons you have (Neutral atom = Atomic #)

-start with the lowest energy level (1s) and keep adding until you have no electrons left

-Each electron has an opposite spin designated 

Ex. Sillicon: 14 electrons

2 electrons in 1s, 2 electrons in 2s, 6 electrons in 2p, 2 electrons in 3s, 2 electrons in 3p

A-E shows the steps taken to write the electron configuration

The 2 electrons in the 3p subshell aren't paired because of Hund's rule: when electrons occupy orbitals of the same energy, they can't be paired up until they have to.

written as: 1s²2s²2p⁶3s²3p²

Ions

negative charged ions: add electrons to the original number of electrons according to its charge

ex. P3- : 15+3

15 being its original # of electrons and 3 added because of its charge

total electrons = 18

written as: 1s²2s²2p⁶3s²3p³

positive charged ions: remove electrons from its original number of electrons according to its charge

ex. Ba2+: 56-2

total electrons: 54

written as: 1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s^24d105p6

Core Notation

-set of electrons that can be divided into two subsets: core electrons and outer electrons

core: set of electrons with the configuration of the nearest noble gas that comes before it

outer: consists of all electrons outside the core (normally takes part in chemical reactions)

ex. Ca

1)the noble gas before calcium is Argon, so you put argon in square brackets

[Ar]

2)then add the remaining electrons

[Ar]4s²

2 EXCEPTIONS: Copper (Cu) and Chromium (Cr)

Cu:  [Ar]4s3d_­¹⁰

^{Cr: [Ar]4s3d5}