Electronic Configuration:

Electronic configuration refers to the arrangement of electrons in the energy levels or orbitals of an atom. It is represented by a series of numbers and letters that indicate the distribution of electrons in different orbitals. Each electron occupies a specific energy level and orbital within an atom.

The electronic configuration is typically written using the following notation:

• Shell (Energy Level): The shells or energy levels are denoted by the numbers 1, 2, 3, and so on, starting from the innermost shell.

For example, let’s consider the electronic configuration of oxygen (O), which has an atomic number of 8:

This electronic configuration indicates that oxygen has:

• 2 electrons in the shell 1 

• 6 electrons in the shell 2 (Incomplete)

  This electronic configuration shows that sodium has:

• 2 electrons in the shell

• 8 electrons in the shell 2

• 1 electron in the shell

OCTET RULE:

The Octet Rule states that atoms tend to gain, lose, or share electrons in order to achieve a stable configuration with a full outer shell of electrons. Atoms want to have eight electrons in their outermost energy level, similar to the electron configuration of noble gasses.

First shell will always have no more than 2 electrons. First shell is called Duplet.
The second shell can have up to 8 electrons. 

Here are the three ways atoms can achieve the Octet Rule: