Electronic Structure of the Atom!

What is the electronic structure of an atom? It's a notation that describes the orbitals in which electrons occupy and the total number of electrons in each orbit. 

Remember back to when we learned about Neils Bohr? The guy in that picture? He proposed that electrons exist in specific energy states and when electrons absorb/emit specific amount of energy, it instantaneously moves from one orbital to the next.


Now for some vocab:
Energy level- amount of energy which electrons in atoms can possess ( "n"= number of energy levels) 
Quantum of energy- energy difference between 2 particular energy levels
Ground state- when electrons of atoms are in their lowest possible energy level
Excited state- when 1 or more of an atom's electrons are in energy levels other than the lowest available level
Orbital- region of space occupied by an electron in particular energy level
Shell- set of all orbitals having the same "n" value
Subshell- set of orbitals of the same type

Orbitals are split into 4 different types: s, p, d, f
Each subshell consists of:
1: s-orbital
3: p-orbital
5: d-orbital
7: f-orbital


Pauli Exclusion Principle: maximum of 2 electrons can be placed in each orbit
This principle means that the maximum number of electrons in each subshell is:
2: s-subshell
6: p-subshell
10- d-subshell
14- f-subshell

This picture will help with writing the electronic configuration of atoms. For neutral atoms:
1) Always start with lowest energy level (Aufbau principle)
2) Figure out how many electron you have (neutral atom=atomic number)
3) Start at lowest energy level (1s) and keep adding on until none is left.

Each electron has an apposite spin designated by upward and downward arrows. An example is silicon. The last line of the picture shows the electronic configuration. Silicon has an atomic number of 14 thus it has 14 electrons at its neutral state. Notice that 2 electrons in 3p occupy separate orbitals and aren't paired? This is due to...
Hund's rule- when electrons occupy orbitals of equal energy, they don't pair up until they have to. 
So in written form: 1s^22s^22p^63s^23p^2
The exponents represent the number of electrons.




Now for writing electronic configurations for ions. 
For negative ions: 
Add electrons (equal to charge) to last unfilled subshell starting where neutral atom left off. An example is N -3
Nitrogen in its neutral state has 7 electrons but with the charge of -3 it is actually 10


For positive ions:
1) Start with neutral atom and remove electrons from outermost shell depending on the charge.
2) If there are electrons in both s and p orbital of the outermost shell, elextrons in the p-orbital are removed first.


Core Notation- way of showing electron configuration in terms of core and outer electrons
A set of electrons belonging to a given atom can be divided into 2 subsets: 
1) Core- set of electrons with configuration of the nearest noble gas (He, Ne, Ar, Kr, etc.) having an atomic number less than that of the atom being considered
2) Outer- consists of all electrons outside the core. Since core electrons, normally don't take part in chemical reactions.


So to find the core notation:
1) Locate the atom and note the noble gas at the end of the row and above the element
2) Write the electron configuration normally. BUT replace the part of the electron configuration corresponding to the configuration of the noble gas.
3) Write the noble gas in square brackets. Ex. [Ne]...
4) Follow the core symbol with the electron configuration of the remaining outer electrons.
Ex. Al: 1s^22s^22p^6 3s^23p^1      
      Ne: 1s^22s^22p^6 Bolded is the core. The rest is the outer. Therefore the core notation is: [Ne] 3s^23p^1


Exceptions!
Instead of: Cr --> [Ar] 4s^23d^4 (One electron short of half-filled subshell)
Cu--> [Ar] 4s^23d^9 (One electron short of a filled subshell)
In actuality:
Cr--> [Ar] 4s^13d^5 (Now both subshells are exactly half-filled)
Cu--> [Ar] 4s^13d^10 (4s^1 is exactly half-filled and 3d^10 is filled)
These 2 atoms indicate: A filled or exactly half-filled d-subshell is especially stable.


Link to awesome quiz to test your genius knowledge. :D

HAHAHA. SO FUNNY.