Electronic Structure - Electron configuration and Valance Electron.

Brief summary through definition and some new vocabulary:

•  Energy level: the amount of energy that electron can possess.

• Ground State: it is when all the electrons are in lowest energy level.
• Excited State: when electrons are in the energy level that different from the lowest level
• Orbital: is the region, like the milky way surrounding around the nucleus that electron occupies in particular energy level
• A shell: is the set of all the orbitals have same energy levels

• Sub-shell: is the set of orbital of the same types (s,p,d,f) 

• Electron Configuration: is the notation that describes the orbital in which electron occupies and the total number of electron each orbital

 

 Or this

Actually, i find the first chart easier to count and do exercise but its up to you. Here's how ->
Usually in test you will be given question like this: Given element Na, write the electron configuration. Don't freak out yet, follow these steps !

1. Look into your periodic table to find that element. In this case, we found Na located in Group IA, period 3
2. Then find the element's proton's number, usually in the top left in the box
3. We all known that if the element is not ion, the number of electron = number of proton
4. So we will be able to know how many electron are there in the element. Okay keep in mind that number.
5. then we follow the route on the periodic table from left to write, top to bottom
6. So finally we just follow that route till we reach that element
7. I can write without think of anything: 1s2 2s2 2p6 3s1

Oh snap i forgot to mention the core notation. Arr i hate chemistry name so much, the core notation is basically the short form of the electron configuration that is easier and faster to write. Its in the form of [X] s(x) p(y) ... Here are steps:

1. Follow steps 1 above
2. Look backward to the previous row, then find the noble gas ON THE BACK ON YOUR ELEMENT, NOT IN FRONT OF
3. Write that noble gas in bracket in this case [Ne]
4. Then continue to write the electron configuration till you reach your element. => [Ne] 3s1

 Here are some scientist contributed to this concept

1. The Pauli Exclusion Principle: in every given energy level, each orbit can only contains 2 electrons

1. The Niel Bohr Principle: electron exists in a specific energy states and can be filled up from low level to high level

1. Hund Rule: the Hund rule states that electron don't pair up unless they have to, that means they will fill out 1/2 the orbit first.

Valance Electron:

It's basically the number of electron in the outer most shell. Or orbital

Ex: The Valance Electron of Na ( [Ne] 3s1 ) is 1 cause there's only 1 electron in the outer most shell