The contents that follows is the substance of basic chrischona2015.orgistry lecture 26. In this class we proceed the discussion of Quantum Numbers and their use in Electron Configurations and also the relationship of electron construction to the regular properties that the elements.

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Electron Configuration

Electron configurations room the summary of whereby the electron are roughly a nucleus. As we learned earlier, each neutral atom has a variety of electrons same to its number of protons. What we will do currently is place those electrons right into an arrangement approximately the cell nucleus that shows their energy and also the form of the orbital in i beg your pardon they space located. Below is a an introduction of the species of orbitals and also how countless electrons each can contain:


So based on what us know around the quantum numbers and also using the chart above, you require 2 electrons to fill an s orbital, 6 electrons to fill a ns orbital, 10 electron to to fill a d orbital and also 14 electrons to fill the f orbital. Yet what us haven"t disputed is exactly how these orbitals get filled...the bespeak of fill.

Order the Fill

The bespeak in which electrons are put into the orbitals is based upon the bespeak of your energy. This is referred to as the Aufbau principle. The lowest power orbitals fill first. Just like the quantum numbers themselves this order was determined by calculation and also is summarized by the adhering to chart:


or you have the right to just use the periodic table:


How to compose an Electron Configuration

The symbols offered for composing the electron configuration start with the covering number (n) adhered to by the type of orbital and finally the superscript indicates how countless electrons are in the orbital.


For example:

Looking at the routine table, you have the right to see that Oxygen has 8 electrons. Based upon the order of fill above, these 8 electrons would certainly fill in the adhering to order 1s, 2s and then 2p. For this reason Oxygen"s electron configuration would be O 1s22s22p4.

Special Cases

Configurations that ions present a special instance of electron configuration and also demonstrate the factor for the development of those ions in the very first place.

If you must write the complete electron construction for one anion, then you are just including additional electrons and the construction is just continued.

For example, we understand that Oxygen always forms 2- ions when it makes an ion. This would add 2 electron to its common configuration making the brand-new configuration: O2- 1s22s22p6. With 10 electron you should note that oxygen"s electron configuration is now exactly the same as Neon"s. Us talked around the fact that ions kind because they can become much more stable v the acquire or ns of electrons to end up being like the noble gases and now you have the right to actually see just how they come to be the same.

The electron configurations for Cations are also made based on the number of electrons yet there is a slight difference in the method they room configured. First you should write their normal electron configuration and also then as soon as you remove electrons you have to take them indigenous the outermost shell. Keep in mind that this is not constantly the same means they to be added.

Here is an example of what i mean:

Iron has actually 26 electron so its normal electron configuration would be: Fe 1s22s22p63s23p64s23d6

When we make a 3+ ion for Iron, we have to take the electrons from the outermost shell an initial so that would be the 4s covering NOT the 3d shell: Fe3+ 1s22s22p63s23p63d5

One other keep in mind on composing electron configurations: A quick cut. As soon as writing few of the lower table configurations the complete configuration have the right to be relatively long. In these cases, you have the right to use the ahead noble gas to abbreviate the construction as shown below. You just have to end up the construction from wherein the noble gas leaves it:



As through every various other topic we have actually covered to date there space exceptions to the order of fill as well. But based upon the electron configurations that room generated, these exceptions are simple to understand.

In the d block, specifically the groups containing Chromium and Copper, there is an exemption in just how they are filled.

Here room the actual configurations:


In this columns, the 4s and 3d

Practice, Practice, Practice

There are many quizzes top top electron configuration you can practice with located here

Orbital Diagrams

Another method to stand for the stimulate of fill for an atom is by making use of an orbital diagram regularly referred to together "the tiny boxes":


The box are used to represent the orbitals and also to display the electrons placed in them. The bespeak of fill is the same but as you have the right to see from over the electrons are inserted singly into the boxes prior to filling them with both electrons. This is dubbed Hund"s Rule: "Half fill prior to you complete fill" and again this rule was established based on energy calculations that shown that this to be the means atoms actually distributed their electrons into the orbitals.

Periodic Properties

One that the really cool things about electron construction is their connection to the regular table. Basically the regular table was built so that elements with comparable electron configurations would be aligned into the same teams (columns).


Periodic Table showing last orbit filled for each element

The routine table shown over demonstrates just how the construction of each aspect was set so the the critical orbital filled is the same other than for the shell. The factor this to be done is the the configuration of an aspect gives the aspect its nature and similar configurations yield similar properties.

Let"s go through few of the periodic Properties that are influenced directly by the electron configuration:

Atomic Size

The dimension of atoms increases going down in the regular table. This have to be intuitive because with each row of the table you are adding a shell (n).

What is no as intuitive is why the size decreases indigenous left to right. Yet again the building and construction of the electron configuration offers us the answer. What are you doing together you go across the regular table? Answer, including protons come the nucleus and including electrons come the valence covering of the element. What is not changing as you cross a period? Answer, the inner shell electrons.

So think of the this way, the inner covering electrons are a shield against the pull of the nucleus. Together you overcome a duration and rise the variety of protons in the cell core you rise its traction but since you room only adding electrons to the brand-new shell the shield is no increasing yet remains the exact same all the means across. This way the traction on the electron being added to the valence covering is enhancing steadily all the method across. What happens if you traction harder top top the electrons? Well, castle come closer come the nucleus and the size of the atom decreases. The effect of the cell core pulling top top the electrons being added throughout a period is referred to as the effective nuclear charge and is calculated as ZEff = #protons - core # Electrons.

So for example the pull felt by Sulfur would be ZEff = 16 - 10 = +6



Electronegativity may be the most crucial of the routine properties you deserve to learn and understand due to the fact that so plenty of other nature are rely on its value. Electronegativity is an atoms capability to pull electrons in the direction of itself.

Electronegativity is typically expressed through the Pauling Scale and also the worths were figured out experimentally. The table listed below shows the scale values for the elements.


The electronegativity values boost from left to right and bottom to height in the routine table excluding the Noble gases. The most electronegative aspect is Fluorine.

From these electronegativity values we deserve to derive the patterns of two other periodic properties: Ionization Energy and Electron Affinity.


Ionization Energy

Ionization power is the amount of power required to eliminate an electron from an atom. Every ionization energies are optimistic values because all of these removals (even those for facets that type positive ions) need input that energy. The more electronegative the element, the greater the ionization eneregy.

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Electron Affinity

The Electron Affinity that an facet is the lot of power gained or released with the enhancement of an electron. The electronegativity and also Electron Affinity boosts in the same pattern in the routine table. Left to right and also bottom to top.