The contents that adheres to is the problem of general benidormclubdeportivo.orgistry lecture 26. In this lecture we proceed the discussion of Quantum Numbers and their usage in Electron Configurations and the connection of electron construction to the regular properties the the elements.

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Electron Configuration

Electron configurations room the summary of where the electron are approximately a nucleus. As we learned earlier, each neutral atom has a variety of electrons same to its variety of protons. What we will certainly do now is location those electrons right into an arrangement around the cell nucleus that suggests their energy and also the form of the orbit in i m sorry they space located. Here is a review of the types of orbitals and also how many electrons each have the right to contain:


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

Order the Fill

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


or you deserve to just usage the regular table:


How to create an Electron Configuration

The symbols used for composing the electron configuration start with the covering number (n) adhered to by the form of orbital and finally the superscript shows how plenty of electrons space in the orbital.


For example:

Looking in ~ the periodic table, you have the right to see that Oxygen has actually 8 electrons. Based upon the stimulate of to fill above, these 8 electrons would certainly fill in the following 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 additionally demonstrate the reason for the development of those ion in the an initial place.

If you need to write the full electron construction for an anion, then you room just including additional electrons and the construction is simply 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 make the brand-new configuration: O2- 1s22s22p6. V 10 electrons you should note that oxygen"s electron construction is now specifically the very same as Neon"s. We talked around the truth that ions kind because they have the right to become more stable v the gain or lose of electron to end up being like the noble gases and also now you deserve to actually see how they end up being the same.

The electron configurations for Cations are also made based on the variety of electrons yet there is a slight difference in the way they space configured. Very first you should write their regular electron configuration and then once you eliminate electrons you have to take them native the outermost shell. Note that this is not constantly the same means they to be added.

Here is an instance of what ns mean:

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

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

One other keep in mind on writing electron configurations: A short cut. As soon as writing several of the reduced table configurations the full configuration can be fairly long. In this cases, you deserve to use the previous noble gas to abbreviate the construction as shown below. Friend just have actually to end up the construction from whereby the noble gas pipeline it:



As with every other topic we have covered to day there room exceptions come the bespeak of fill as well. But based on the electron construction that are generated, these exceptions are straightforward to understand.

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

Here space the actual configurations:


In these columns, the 4s and also 3d

Practice, Practice, Practice

There are numerous quizzes ~ above electron configurations you can practice with situated here

Orbital Diagrams

Another method to stand for the bespeak of fill for an atom is by using an orbital diagram often referred to as "the small boxes":


The crate are used to stand for the orbitals and also to display the electrons put in them. The order of fill is the same yet as you deserve to see from over the electrons are placed singly into the boxes prior to filling them through both electrons. This is dubbed Hund"s Rule: "Half fill before you complete fill" and also again this preeminence was established based upon energy calculations that shown that this to be the method atoms actually dispersed their electrons into the orbitals.

Periodic Properties

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


Periodic Table showing last orbital filled because that each element

The routine table shown over demonstrates just how the construction of each aspect was aligned so the the last orbital to fill is the same except for the shell. The reason this to be done is the the construction of an facet gives the aspect its nature and similar configurations yield similar properties.

Let"s walk through some of the regular Properties that are influenced straight by the electron configuration:

Atomic Size

The size of atoms increases going down in the periodic table. This need to be intuitive since with each row of the table girlfriend are adding a covering (n).

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

So think of the this way, the inner covering electrons room a shield against the pull of the nucleus. Together you cross a duration and rise the variety of protons in the cell nucleus you increase its pull but because you space only adding electrons come the brand-new shell the shield is no increasing yet remains the exact same all the means across. This method the traction on the electron being included to the valence shell is raising steadily every the method across. What happens if you traction harder on the electrons? Well, castle come closer come the nucleus and the dimension of the atom decreases. The impact of the nucleus pulling top top the electrons gift added throughout a period is called the efficient nuclear charge and is calculated as ZEff = #protons - main point # Electrons.

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



Electronegativity might be the most essential of the periodic properties you can learn and understand due to the fact that so numerous other properties are depend on that value. Electronegativity is one atoms capability to pull electrons in the direction of itself.

Electronegativity is normally expressed by the Pauling Scale and the values were determined experimentally. The table listed below shows the scale values because that the elements.


The electronegativity values increase from left to right and bottom to height in the routine table excluding the Noble gases. The many electronegative element is Fluorine.

From this electronegativity worths we can derive the fads of two other periodic properties: Ionization Energy and also Electron Affinity.


Ionization Energy

Ionization power is the amount of power required to remove an electron from an atom. All ionization energies are confident values because every one of these removals (even those for facets that form positive ions) need input that energy. The more electronegative the element, the higher the ionization eneregy.

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Electron Affinity

The Electron Affinity the an aspect is the amount of power gained or released with the addition of one electron. The electronegativity and also Electron Affinity boosts in the exact same pattern in the regular table. Left to right and also bottom come top.