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Chemistry 1: Electronic Configuration of Atoms

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• Electrons and Energy

• Atomic orbitals

• Möller's rule

• Orbital superscripts

• Exaple

• Electronic configuration of ions

• Example

• Extra material

Electrons and Energy

Each atom is composed of a nucleus and its electron cloud, this nucleus in turn is composed of two types of particles, protons and neutrons with positive and neutral charges. In each of the shells there are the electrons, which have negative charges and are accommodated in each shell in a certain way.

Although all electrons have the same charge and the same mass, each of them has a different amount of energy and this is related to their proximity to the nucleus. The lowest energy level shell is closest to the nucleus, while the highest energy level shell are further away from it.
Electrons that have a high energy content and that are in the last shell are more weakly bound to the atom, so that it is easier for it to bond with others and form compounds.


Möller's Rule

There is a table known as the Moller diagram. This is used as a method to order the energy levels and their orbitals to distribute the electrons following the direction of the diagonals.


Orbital superscripts

To carry out the arrangement of the electrons in the orbitals, superindices are used. For example: 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2...

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These superscripts indicate how many electrons are in each shell, within which fit according to the letter. In the S shells only 2 electrons fit, in the P shells 6 electrons fit, in the D shells 10 electrons fit and in the F shells 14 electrons fit.


If it is known that Chromium (Cr) has an atomic number Z = 24. What is its electronic configuration?

If we distribute the electrons according to Moller's rule, wich are 24, we'll get:
1s2 2s2 2p6 3s2 3p6 4s2 3d4

In this example you can count the superscripts to verify that there are 24 electrons in total over all the shells. Even though the shell D is capable to have even 10 electrons,in this case this shell only has 4.

Electronic configuration of ions

An Ion is that molecule of an element that contains a charge other than neutral, that means it has more (or fewer) electrons than the element in its normal form.

As with any atom of any element, the electronic configuration of the ions can also be extracted; For these, it must be taken into account that if we are given a negatively charged atom it means that it has more electrons, while if we are given a positively charged atom it means that it has fewer electrons.

Ion example

What is the electron configuration of the anion N3− if the Nitrogen atom has an atomic number Z = 7?

Nitrogen's atomic number is 7, so in a neutral state, it would have 7 electrons. However, they tell us that this anion has a negative charge of 3, which means that it has gained 3 electrons. With what we have that this anion has 10 electrons in total.

Applying Moller's rule, its electronic configuration is:

1s2 2s2 2p6

© 2021 Daniela Alejandra Rodríguez Cerda

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