Electronic Structure + Number of Valence Electrons

Electronic Structure of the Atom

First of, let's begin with some terminologies.

Electronic Configuration: notation that describes the orbitals in which the electrons occupy and the total number of electrons in each orbital

Energy Level (n): amount of energy which an electron can possess

-the energy difference between 2 particular energy levels is called the quantum of energy

Ground state: all electrons in their lowest energy level (n=1)

Excited State: one or more electron that is not in the lowest energy level (n=2/3/4)

Orbital: actual region of space occupied by an electron

Shell: the set of all orbitals having the same n-values (same as periods on the periodic table)

Sub-Shell: a set of orbitals of the same type

Above is a chart of the maximum number of electron in an energy level

Here is the order of writing electronic configuration.

However, things become a little different when it comes to positive ions.

-If there are electrons in both s-, p- orbitals of the outermost shell, the electrons in the p-orbitals are removed first

Core Notation

-the CORE of an atom is the set of electrons with the configuration of the nearest noble gas that comes before it

-the OUTER electrons consist of all electrons outside the core

Basically instead of writing a long electronic configuration, we have a simplified [noble gas] + outer electrons instead

Now let's do one example which consists of electronic configuration, positive ions, and core notation.

Ex/ write the full notation and core notation for Na and Na+

Na: 1s2 2s2 2p2 3s1  -->  [Ne] 3s1

Na+: 1s2 2s2 2p2 3s1  --> [Ne]

This video will explain more about writing electronic configuration if you have any further questions~ ^ ^

*EXCEPTIONS

Copper - instead of [Ar] 4s2 3d9, it is actually 4s1 3d10

Chromium - instead of [Ar] 4s2 3d4, it is actually 4s1 3d5

Predicting the number of Valance Electrons

Here is a Bohr diagram for Phosphorous, which could help us understand the topic of valence electrons a lot better.
Valence Electrons are also called react-able electrons because they participate in bonding with other atoms.
They are in the outermost shell; as we can see in the picture, there are 5 valence electrons in phosphorous.
We have learned that the first shell could contain 2 electrons, and after that every shell contains as many as 8.
We can simply use one element's atomic number to find out how many valence electrons there are.

An open shell contains less than its maximum number of electrons, phosphorous in the picture is an example.
A closed shell on the other hand is the complete opposite, it contains exactly its maximum number of electrons.

Let's practice:
Sodium - Na 's core notation is [Ne] 3s^1
By looking at the core notation, we can easily figure out the number of valence electrons.
Just follow the rule of counting only the s- and p- sub-shells in the core notation.
In this case, Na has one valence electron.