The content that follows is the substance of basic rebab.netistry lecture 26. In this lecture we proceed the conversation of Quantum Numbers and their usage in Electron Configurations and the relationship of electron construction to the routine properties of the elements.

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Electron Configuration

Electron configurations are the summary of where the electron are about a nucleus. As we learned earlier, each neutral atom has a variety of electrons same to its variety of protons. What we will do now is place those electrons right into an arrangement about the nucleus that shows their energy and the form of the orbital in which they room located. Right here is a an overview of the varieties of orbitals and also how numerous electrons each can contain:


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

Order the Fill

The order in which electrons are placed into the orbitals is based on the bespeak of their energy. This is referred to as the Aufbau principle. The lowest energy orbitals to fill first. As with the quantum numbers themselves this order was identified by calculation and also is summary by the complying with chart:


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


How to compose an Electron Configuration

The symbols supplied for writing the electron configuration begin with the shell number (n) complied with by the kind of orbital and finally the superscript shows how numerous electrons room in the orbital.


For example:

Looking in ~ the regular table, you have the right to see that Oxygen has actually 8 electrons. Based upon the stimulate of fill above, this 8 electrons would certainly fill in the adhering to order 1s, 2s and then 2p. So Oxygen"s electron configuration would certainly be O 1s22s22p4.

Special Cases

Configurations the ions existing a special case of electron configuration and also demonstrate the reason for the formation of those ion in the first place.

If you must write the complete electron construction for one anion, climate you space just including additional electrons and also the construction is merely continued.

For example, we know that Oxygen always forms 2- ions once it provides an ion. This would include 2 electrons to its common configuration do the brand-new configuration: O2- 1s22s22p6. With 10 electrons you should note that oxygen"s electron construction is now precisely the exact same as Neon"s. We talked about the reality that ions form because they can become more stable v the get or ns of electron to become like the noble gases and also now you can actually see how they come to be the same.

The electron configurations for Cations are likewise made based on the number of electrons however there is a slight distinction in the means they are configured. First you should write their typical electron configuration and then as soon as you remove electrons you need to take them indigenous the outermost shell. Keep in mind that this is not always the same method they to be added.

Here is an example of what i mean:

Iron has 26 electrons so its typical electron configuration would be: Fe 1s22s22p63s23p64s23d6

When us make a 3+ ion for Iron, we need to take the electrons from the outermost shell very first so that would be the 4s shell NOT the 3d shell: Fe3+ 1s22s22p63s23p63d5

One other keep in mind on composing electron configurations: A quick cut. When writing few of the lower table construction the total configuration can be reasonably long. In this cases, you have the right to use the previous noble gas to abbreviation the configuration as presented below. You just have actually to complete the construction from where the noble gas pipeline it:



As v every various other topic we have actually covered to day there are exceptions come the stimulate of fill as well. But based on the electron configurations that are generated, these exceptions are easy to understand.

In the d block, specifically the teams containing Chromium and Copper, over there is an exception in how they space filled.

Here are the really configurations:


In these columns, the 4s and also 3d

Practice, Practice, Practice

There are numerous quizzes ~ above electron configuration you have the right to practice with situated here

Orbital Diagrams

Another means to represent the order of fill for one atom is by making use of an orbital diagram frequently referred to as "the small boxes":


The crate are provided to stand for the orbitals and also to present the electrons placed in them. The order of to fill is the same but as you deserve to see from over the electron are inserted singly into the boxes prior to filling them with both electrons. This is called Hund"s Rule: "Half fill before you complete fill" and again this dominance was established based on energy calculations that suggested that this was the means atoms actually dispersed their electrons right into the orbitals.

Periodic Properties

One of the yes, really cool things around electron construction is their relationship to the regular table. Basically the regular table was built so that elements with comparable electron configurations would certainly be aligned into the same teams (columns).


Periodic Table mirroring last orbital filled for each element

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

Let"s walk through several of the periodic Properties that space influenced straight by the electron configuration:

Atomic Size

The dimension of atoms boosts going down in the routine table. This have to be intuitive because with each heat of the table you are adding a covering (n).

What is no as intuitive is why the size decreases from left to right. However again the construction of the electron configuration provides us the answer. What room you doing as you go across the routine table? Answer, including protons come the cell core and including electrons come the valence shell of the element. What is not an altering as you cross a period? Answer, the inner shell electrons.

So think of it this way, the inner shell electrons room a shield against the traction of the nucleus. As you cross a duration and rise the variety of protons in the cell core you rise its pull but since you room only including electrons to the brand-new shell the shield is not increasing but remains the exact same all the means across. This way the traction on the electrons being included to the valence covering is raising steadily every the method across. What happens if you pull harder on the electrons? Well, they come closer to the nucleus and the dimension of the atom decreases. The effect of the cell nucleus pulling top top the electrons gift added across a duration is dubbed the efficient nuclear charge and is calculated together ZEff = #protons - main point # Electrons.

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



Electronegativity might be the most crucial of the routine properties you can learn and also understand since so numerous other nature are count on its value. Electronegativity is one atoms capability to pull electrons towards itself.

Electronegativity is generally expressed by the Pauling Scale and the values were figured out experimentally. The table below shows the scale values because that the elements.


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

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


Ionization Energy

Ionization energy is the lot of energy required to remove an electron from an atom. All ionization energies are optimistic values because all of these removals (even those for aspects that type positive ions) call for input of energy. The much more electronegative the element, the greater the ionization eneregy.

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Electron Affinity

The Electron Affinity the an element is the lot of energy gained or released with the enhancement of one electron. The electronegativity and also Electron Affinity increases in the very same pattern in the regular table. Left come right and bottom to top.