The contents that complies with is the substance of general piersonforcongress.comistry lecture 26. In this lecture we continue the discussion of Quantum Numbers and also their usage in Electron Configurations as well as the connection of electron configuration to the regular properties that the elements.

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Electron Configuration

Electron configurations space the an introduction of whereby the electron are approximately a nucleus. Together we learned earlier, every neutral atom has a variety of electrons equal to its number of protons. What we will certainly do currently is place those electrons into an arrangement roughly the cell core that shows their energy and the shape of the orbital in i beg your pardon they space located. Right here is a review of the types of orbitals and how plenty of electrons each deserve to contain:


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

Order that Fill

The order in which electron are inserted into the orbitals is based upon the order of your energy. This is described as the Aufbau principle. The lowest energy orbitals fill first. Similar to the quantum numbers themselves this bespeak was determined by calculation and is summarized by the adhering to chart:


or you deserve to just usage the regular table:


How to write an Electron Configuration

The symbols offered for writing the electron configuration start with the shell number (n) followed by the form of orbital and finally the superscript shows how numerous electrons space in the orbital.


For example:

Looking in ~ the routine table, you deserve to see that Oxygen has actually 8 electrons. Based upon the bespeak of fill above, these 8 electrons would certainly fill in the complying with order 1s, 2s and then 2p. So Oxygen"s electron configuration would be O 1s22s22p4.

Special Cases

Configurations of ions current a special situation of electron configuration and additionally demonstrate the factor for the development of those ions in the first place.

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

For example, we know that Oxygen always forms 2- ions once it makes an ion. This would include 2 electrons to its typical configuration do the brand-new configuration: O2- 1s22s22p6. With 10 electrons you must note that oxygen"s electron configuration is now precisely the same as Neon"s. We talked about the fact that ions kind because they can become more stable with the gain or ns of electron to end up being like the noble gases and also now you can actually see how they end up being the same.

The electron configurations because that Cations are additionally made based on the variety of electrons but there is a slight distinction in the way they space configured. Very first you must write their normal electron configuration and also then as soon as you remove electrons you have 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 ns mean:

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

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

One other keep in mind on creating electron configurations: A short cut. When writing few of the reduced table configuration the complete configuration deserve to be reasonably long. In these cases, you have the right to use the vault noble gas to abbreviation the configuration as presented below. Girlfriend just have actually to end up the configuration from where the noble gas pipeline it:



As through every various other topic we have covered to date there space exceptions come the stimulate of fill as well. But based on the electron configurations that room generated, this exceptions are simple to understand.

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

Here space the yes, really configurations:


In these columns, the 4s and also 3d

Practice, Practice, Practice

There are many quizzes on electron construction you can practice with located here

Orbital Diagrams

Another method to stand for the stimulate of to fill for one atom is by utilizing an orbit diagram frequently referred to together "the little boxes":


The box are supplied to stand for the orbitals and also to present the electrons put in them. The order of fill is the same however as you deserve to see from above the electron are inserted singly into the boxes prior to filling them v both electrons. This is dubbed Hund"s Rule: "Half fill prior to you complete fill" and again this dominion was established based on energy calculations that indicated that this was the means atoms actually dispersed their electrons into the orbitals.

Periodic Properties

One of the really cool things about electron configurations is their partnership to the regular table. Usually the regular table was created so that elements with similar electron configurations would be aligned into the same teams (columns).


Periodic Table showing last orbit filled for each element

The routine table shown over demonstrates just how the configuration of each element was set so that the last orbital fill is the same other than for the shell. The reason this was done is the the construction of an aspect gives the facet its properties and comparable configurations yield comparable properties.

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

Atomic Size

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

What is no as intuitive is why the dimension decreases native left come right. But again the construction of the electron configuration gives us the answer. What are you doing together you go throughout 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 shell electrons.

So think of the this way, the inner covering electrons are a shield versus the pull of the nucleus. Together you overcome a period and increase the variety of protons in the nucleus you increase its traction but because you room only adding electrons come the new shell the shield is not increasing yet remains the same all the means across. This means the pull on the electrons being included to the valence covering is boosting steadily every the way across. What wake up if you pull harder top top the electrons? Well, they come closer come the nucleus and also the dimension of the atom decreases. The impact of the cell nucleus pulling on the electrons being added across a duration is called the reliable nuclear charge and also is calculated together ZEff = #protons - core # Electrons.

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



Electronegativity might be the most essential of the routine properties you have the right to learn and also understand because so plenty of other properties are rely on its value. Electronegativity is one atoms ability to traction electrons towards itself.

Electronegativity is normally expressed through the Pauling Scale and also the worths were identified experimentally. The table listed below shows the scale values for the elements.


The electronegativity values increase from left come right and also bottom to optimal in the routine table excluding the Noble gases. The most electronegative facet is Fluorine.

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


Ionization Energy

Ionization power is the quantity of energy required to remove an electron indigenous an atom. Every ionization energies are confident 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 higher the ionization eneregy.

See more: What Is The Difference Between All Ready And Already And All Ready

Electron Affinity

The Electron Affinity that an element is the lot of energy gained or released v the addition of one electron. The electronegativity and Electron Affinity boosts in the exact same pattern in the periodic table. Left to right and also bottom come top.