The contents that follows is the substance of basic starrkingschool.netistry great 26. In this lecture we continue the conversation of Quantum Numbers and also their use in Electron Configurations and also the partnership of electron construction to the periodic properties that the elements.

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Electron Configuration

Electron configurations space the review of whereby the electron are around a nucleus. As we learned earlier, each neutral atom has a variety of electrons same to its number of protons. What we will certainly do now is ar those electrons into an arrangement roughly the cell core that indicates their energy and the form of the orbital in which they are located. Below is a an overview of the species of orbitals and also how many electrons each can contain:


So based on what we know about the quantum numbers and using the graph above, you need 2 electrons to to fill an s orbital, 6 electrons to fill a p orbital, 10 electron to to fill a d orbital and 14 electron to fill the f orbital. But what us haven"t disputed is exactly how these orbitals acquire filled...the bespeak of fill.

Order of Fill

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


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


How to write an Electron Configuration

The symbols supplied for composing the electron configuration begin with the shell number (n) followed by the type of orbital and finally the superscript shows how many electrons are in the orbital.


For example:

Looking at the regular table, you have the right to see the Oxygen has actually 8 electrons. Based upon the stimulate of fill above, these 8 electrons would certainly 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 present a special case of electron configuration and also demonstrate the factor for the development of those ion in the an initial place.

If you need to write the full electron construction for one anion, then you room just including additional electrons and also the configuration is simply continued.

For example, we understand that Oxygen constantly forms 2- ions as soon as it makes an ion. This would include 2 electron to its typical configuration make the brand-new configuration: O2- 1s22s22p6. With 10 electron you have to note the oxygen"s electron construction is now exactly the same as Neon"s. We talked about the truth that ions form because they can become much more stable through the get or lose of electron to end up being like the noble gases and now you deserve to actually see exactly how they become the same.

The electron configurations for Cations are additionally made based on the number of electrons yet there is a slight distinction in the method they are configured. Very first you have to write their typical 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 instance of what i mean:

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

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

One other keep in mind on creating electron configurations: A brief cut. When writing few of the lower table construction the complete configuration deserve to be fairly long. In these cases, you deserve to use the previous noble gas to abbreviate the configuration as shown below. Girlfriend just have actually to finish the construction from whereby the noble gas pipeline it:



As v every other topic we have actually covered to date there are exceptions to the bespeak of fill together well. But based upon the electron configuration that space generated, these exceptions are easy to understand.

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

Here are the actual configurations:


In these columns, the 4s and 3d

Practice, Practice, Practice

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

Orbital Diagrams

Another method to represent the bespeak of to fill for an atom is by using an orbit diagram regularly referred to together "the small boxes":


The boxes are supplied to represent the orbitals and to show the electrons inserted in them. The bespeak of fill is the same however as you have the right to see from above the electron are placed singly right into the boxes before filling them with both electrons. This is referred to as Hund"s Rule: "Half fill prior to you full fill" and again this dominion was established based upon energy calculations that suggested that this to be the means atoms actually distributed their electrons into the orbitals.

Periodic Properties

One that the really cool things about electron configurations is their relationship to the regular table. Usually the periodic table was constructed so that elements with comparable electron configurations would be aligned right into the same teams (columns).


Periodic Table mirroring last orbital filled because that each element

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

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

Atomic Size

The size of atoms increases going down in the routine table. This need to be intuitive due to the fact that with each heat of the table girlfriend are adding a shell (n).

What is not 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 throughout the routine table? Answer, including protons to the cell nucleus and including electrons to the valence covering of the element. What is not an altering as you overcome a period? Answer, the inner covering electrons.

So think of that this way, the inner shell electrons space a shield against the traction of the nucleus. Together you overcome a period and boost the variety of protons in the nucleus you boost its traction but because you space only adding electrons to the brand-new shell the shield is no increasing however remains the very same all the method across. This way the pull on the electron being included to the valence shell is boosting steadily every the means across. What happens if you pull harder ~ above the electrons? Well, they come closer come the nucleus and also the size of the atom decreases. The impact of the cell nucleus pulling ~ above the electrons being added across a duration is dubbed the effective nuclear charge and also is calculated together ZEff = #protons - main point # Electrons.

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



Electronegativity may be the most vital of the periodic properties you deserve to learn and also understand due to the fact that so countless other properties are count on that is value. Electronegativity is one atoms ability to traction electrons in the direction of itself.

Electronegativity is typically expressed by the Pauling Scale and also the worths were determined experimentally. The table listed below shows the range values because that the elements.


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

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


Ionization Energy

Ionization power is the lot of energy required to eliminate an electron native an atom. Every ionization energies are hopeful values because every one of these removals (even those for facets that form positive ions) call for input that energy. The much more electronegative the element, the greater 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 enhancement of an electron. The electronegativity and Electron Affinity rises in the very same pattern in the periodic table. Left to right and bottom come top.