The content that complies with is the problem of general historicsweetsballroom.comistry lecture 26. In this great we continue the discussion of Quantum Numbers and their usage in Electron Configurations and the relationship of electron configuration to the periodic properties that the elements.

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Electron Configuration

Electron configurations room the summary of wherein the electrons are about a nucleus. As we learned earlier, every neutral atom has a variety of electrons same to its number of protons. What we will certainly do currently is place those electrons into an arrangement approximately the cell nucleus that shows their energy and also the shape of the orbital in which they are located. Here is a an overview of the varieties of orbitals and how plenty of electrons each have the right to contain:


So based on what us know about the quantum numbers and also using the graph above, you need 2 electrons to fill an s orbital, 6 electron to to fill a ns orbital, 10 electron to fill a d orbital and 14 electron to to fill the f orbital. However what us haven"t debated is just how these orbitals get filled...the order of fill.

Order of Fill

The order in which electron are put into the orbitals is based on the bespeak of your energy. This is referred to as the Aufbau principle. The lowest energy orbitals fill first. Just like the quantum number themselves this bespeak was established by calculation and also is summarized by the complying with chart:


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


How to create an Electron Configuration

The symbols provided for composing the electron configuration start with the covering number (n) complied with by the form of orbital and finally the superscript suggests how numerous electrons space in the orbital.


For example:

Looking at the routine table, you deserve to see the Oxygen has 8 electrons. Based on the bespeak of to fill above, these 8 electrons would fill in the complying with order 1s, 2s and also then 2p. For this reason Oxygen"s electron configuration would be O 1s22s22p4.

Special Cases

Configurations that ions existing a special instance of electron construction and also demonstrate the factor for the formation of those ions in the an initial place.

If you should write the complete electron configuration for one anion, climate you are just adding additional electrons and the construction is simply continued.

For example, we recognize that Oxygen constantly forms 2- ions as soon as it makes an ion. This would include 2 electron to its common configuration make the new configuration: O2- 1s22s22p6. V 10 electron you need to note that oxygen"s electron construction is now exactly the exact same as Neon"s. Us talked about the fact that ions type because they deserve to become more stable through the get or lose of electron to become like the noble gases and now you can actually see just how they come to be the same.

The electron configurations for Cations are also made based on the number of electrons however there is a slight distinction in the method they space configured. Very first you must write their regular electron configuration and then once you eliminate electrons you have to take them from the outermost shell. Note that this is not always the same means they were added.

Here is an example of what i mean:

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

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

One other keep in mind on creating electron configurations: A brief cut. As soon as writing few of the reduced table configuration the total configuration can be reasonably long. In this 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 with every various other topic we have covered to day there space exceptions to the bespeak of fill together well. But based upon the electron configuration that space generated, these exceptions are simple to understand.

In the d block, specifically the teams containing Chromium and Copper, there is an exemption in exactly how they room filled.

Here are the really configurations:


In these columns, the 4s and 3d

Practice, Practice, Practice

There are lots of quizzes on electron construction you deserve to practice with situated here

Orbital Diagrams

Another method to stand for the stimulate of fill for one atom is by using an orbit diagram often referred to as "the tiny boxes":


The boxes are supplied to stand for the orbitals and to display the electrons put in them. The stimulate of to fill is the same but as you deserve to see from over the electrons are inserted singly into the boxes before filling them v both electrons. This is dubbed Hund"s Rule: "Half fill prior to you complete fill" and also again this preeminence was established based upon energy calculations that indicated that this was the means atoms actually spread their electrons right into the orbitals.

Periodic Properties

One that the yes, really cool things around electron construction is their connection to the routine table. Basically the routine table was built so that aspects with similar electron configurations would certainly be aligned into the same groups (columns).


Periodic Table mirroring last orbit filled because that each element

The routine table shown above demonstrates exactly how the construction of each facet was aligned so the the critical orbital to fill is the same except for the shell. The reason this was done is the the configuration of an element gives the aspect its properties and comparable configurations yield similar properties.

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

Atomic Size

The size of atoms rises going under in the routine table. This have to be intuitive because with each heat of the table friend are adding a covering (n).

What is no as intuitive is why the dimension decreases indigenous left come right. However again the construction of the electron configuration provides us the answer. What room you doing together you go across the periodic table? Answer, adding protons to the nucleus and including electrons come the valence covering of the element. What is not changing as you cross a period? Answer, the inner covering electrons.

So think of the this way, the inner shell electrons are a shield against the pull of the nucleus. Together you overcome a period and boost the variety of protons in the nucleus you rise its pull but due to the fact that you space only including electrons to the brand-new shell the shield is no increasing but remains the exact same all the means across. This way the pull on the electron being included to the valence shell is raising steadily all the means across. What wake up if you pull harder top top the electrons? Well, castle come closer come the nucleus and also the size of the atom decreases. The result of the nucleus pulling ~ above the electrons being added throughout a duration is referred to as the efficient nuclear charge and is calculated together ZEff = #protons - main point # Electrons.

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



Electronegativity might be the most essential of the regular properties you have the right to learn and understand since so countless other nature are rely on that value. Electronegativity is one atoms capacity to traction electrons towards itself.

Electronegativity is typically expressed through the Pauling Scale and also the values were identified experimentally. The table below shows the scale values because that the elements.


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

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


Ionization Energy

Ionization power is the lot of energy required to eliminate an electron indigenous an atom. Every ionization energies are hopeful values because all of these removals (even those for aspects that form positive ions) require input of energy. The more electronegative the element, the higher the ionization eneregy.

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Electron Affinity

The Electron Affinity of an element is the amount of energy gained or released v the enhancement of one electron. The electronegativity and also Electron Affinity rises in the exact same pattern in the routine table. Left to right and also bottom come top.