The contents that complies with is the substance of general tasiilaq.netistry lecture 26. In this class we continue the discussion of Quantum Numbers and also their use in Electron Configurations as well as the relationship of electron configuration to the regular properties the the elements.

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Electron Configuration

Electron configurations space the an introduction of where the electron are approximately a nucleus. As we learned earlier, every neutral atom has actually a number of electrons same to its number of protons. What we will do currently is location those electrons right into an arrangement roughly the cell nucleus that suggests their energy and also the form of the orbit in which they space located. Here is a review of the varieties of orbitals and also how countless electrons each have the right to contain:


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

Order the Fill

The order in which electron are placed into the orbitals is based on the order of their energy. This is described as the Aufbau principle. The lowest power orbitals fill first. Just like the quantum number themselves this bespeak was determined by calculation and is summarized by the complying with chart:


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


How to create an Electron Configuration

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


For example:

Looking at the regular table, you can see the Oxygen has 8 electrons. Based on the bespeak of fill above, this 8 electrons would fill in the following 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 very first place.

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

For example, we know that Oxygen constantly forms 2- ions once it provides an ion. This would include 2 electron to its regular configuration making the new configuration: O2- 1s22s22p6. V 10 electrons you have to note that oxygen"s electron configuration is now specifically the exact same as Neon"s. Us talked about the truth that ions kind because they have the right to become more stable v the get or lose of electron to become like the noble gases and also now you deserve to actually see how they become the same.

The electron configurations because that Cations are likewise made based upon the number of electrons but there is a slight distinction in the method they are configured. First you need to write their normal electron configuration and also then as soon as you eliminate electrons you need to take them from the outermost shell. Keep in mind that this is not constantly the same method they to be added.

Here is an example of what i mean:

Iron has actually 26 electrons so its common 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 shell NOT the 3d shell: Fe3+ 1s22s22p63s23p63d5

One other note on writing electron configurations: A brief cut. As soon as writing several of the lower table configurations the full configuration can be fairly long. In these cases, you deserve to use the ahead noble gas to abbreviation the construction as presented below. Girlfriend just have actually to complete the construction from whereby the noble gas leaves it:



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

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

Here are the actual configurations:


In this columns, the 4s and 3d

Practice, Practice, Practice

There are lots of quizzes top top electron configuration you have the right to practice with situated here

Orbital Diagrams

Another method to represent the bespeak of fill for an atom is by making use of an orbital diagram often referred to together "the little boxes":


The boxes are offered to represent the orbitals and also to display the electrons placed in them. The order of fill is the same yet as you deserve to see from above the electrons are inserted singly into the boxes prior to filling them through both electrons. This is referred to as Hund"s Rule: "Half fill prior to you full fill" and again this ascendancy was established based upon energy calculations that suggested that this was the way atoms actually spread their electrons into the orbitals.

Periodic Properties

One that the yes, really cool things around electron configuration is their connection to the periodic table. Basically the periodic table was created so that elements with comparable electron configurations would be aligned right into the same teams (columns).


Periodic Table mirroring last orbit filled because that each element

The regular table shown over demonstrates how the configuration of each element was to adjust so the the last orbital fill is the same except for the shell. The factor this to be done is the the configuration of an facet gives the aspect its properties and comparable configurations yield similar properties.

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

Atomic Size

The size of atoms rises going down in the periodic table. This must be intuitive because with each heat of the table you are adding a shell (n).

What is no as intuitive is why the size decreases from left come right. Yet again the building of the electron configuration gives us the answer. What are you doing as you go across the periodic table? Answer, adding protons to the cell core and adding electrons to the valence shell of the element. What is not transforming as you overcome a period? Answer, the inner covering electrons.

So think of that this way, the inner covering electrons space a shield against the traction of the nucleus. As you overcome a period and boost the number of protons in the cell nucleus you boost its traction but because you room only including electrons to the new shell the shield is not increasing yet remains the very same all the method across. This means the traction on the electron being included to the valence shell is increasing steadily all the method across. What happens if you traction harder ~ above the electrons? Well, they come closer to the nucleus and also the size of the atom decreases. The effect of the cell core pulling on the electrons gift added throughout a duration is referred to as the effective nuclear charge and also is calculated as ZEff = #protons - main point # Electrons.

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



Electronegativity may be the most crucial of the routine properties you can learn and understand since so many other nature are count on its value. Electronegativity is an atoms capability to traction electrons towards itself.

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


The electronegativity values rise from left come right and also bottom to optimal in the periodic table not included the Noble gases. The many electronegative aspect is Fluorine.

From these electronegativity values we have the right to derive the fads of two various other periodic properties: Ionization Energy and Electron Affinity.


Ionization Energy

Ionization energy is the lot of power required to remove an electron from an atom. All ionization energies are confident values because all of these removals (even those for elements that kind positive ions) need 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 through the addition of one electron. The electronegativity and also Electron Affinity boosts in the very same pattern in the periodic table. Left to right and also bottom to top.