The content that adheres to is the problem of general aramuseum.orgistry lecture 26. In this class we continue the discussion of Quantum Numbers and also their usage in Electron Configurations as well as the relationship of electron configuration to the periodic properties of the elements.

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Electron Configuration

Electron configurations are the an introduction of where the electrons are approximately a nucleus. Together 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 about the nucleus that suggests their energy and the shape of the orbit in i beg your pardon they space located. Below is a an introduction of the species of orbitals and how numerous electrons each can contain:


So based upon what us know about the quantum numbers and using the graph above, you require 2 electrons to to fill an s orbital, 6 electrons to to fill a p orbital, 10 electron to fill a d orbital and also 14 electrons to to fill the f orbital. However what we haven"t discussed is just how these orbitals obtain filled...the stimulate of fill.

Order of Fill

The order in which electron are inserted into the orbitals is based upon the bespeak of their energy. This is described as the Aufbau principle. The lowest energy orbitals to fill first. As with the quantum number themselves this order was determined by calculation and also is summary by the complying with chart:


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


How to create an Electron Configuration

The symbols provided for creating the electron configuration start with the covering number (n) complied with by the type of orbital and also finally the superscript indicates how numerous electrons room in the orbital.


For example:

Looking at the periodic table, you can see the Oxygen has 8 electrons. Based on the order of fill above, this 8 electrons would certainly fill in the adhering to order 1s, 2s and then 2p. So Oxygen"s electron configuration would be O 1s22s22p4.

Special Cases

Configurations of ions current a special case of electron configuration and likewise demonstrate the factor for the development of those ion in the an initial place.

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

For example, we understand that Oxygen constantly forms 2- ions once it provides an ion. This would include 2 electrons to its common configuration do the new configuration: O2- 1s22s22p6. Through 10 electron you should note the oxygen"s electron configuration 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 obtain or loss of electron to end up being like the noble gases and also now you deserve to actually see how they become the same.

The electron configurations for Cations are also made based upon the variety of electrons however there is a slight difference in the means they are configured. Very first you should write their normal electron configuration and then when you eliminate electrons you have to take them indigenous the outermost shell. Note that this is not always the same method they were added.

Here is an instance of what i mean:

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

When us 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 note on creating electron configurations: A quick cut. Once writing few of the reduced table configuration the full configuration can be reasonably long. In this cases, you can use the ahead noble gas to abbreviation the construction as presented below. You just have actually to finish the configuration from whereby the noble gas leaves it:



As v every various other topic we have actually covered to day there space exceptions to the stimulate of fill as well. But based on the electron configuration that are generated, these exceptions are easy to understand.

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

Here are the yes, really configurations:


In this columns, the 4s and 3d

Practice, Practice, Practice

There are many quizzes ~ above electron configurations you deserve to practice with situated here

Orbital Diagrams

Another way to stand for the bespeak of to fill for one atom is by using an orbit diagram often referred to together "the small boxes":


The boxes are used to stand for the orbitals and also to show the electrons put in them. The order of fill is the same however as you deserve to see from above 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 full fill" and again this rule was established based on energy calculations that indicated that this to be the method atoms actually spread their electrons right into the orbitals.

Periodic Properties

One of the really cool things about electron construction is their relationship to the routine table. Basically the routine table was created so that elements with comparable electron configurations would be aligned right into the same groups (columns).


Periodic Table showing last orbit filled for each element

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

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

Atomic Size

The dimension of atoms boosts going down in the regular table. This should be intuitive since with each row of the table you are adding a covering (n).

What is no as intuitive is why the dimension decreases from left to right. However again the building of the electron configuration offers us the answer. What space you doing as you go throughout the regular table? Answer, including protons to the nucleus and adding electrons come the valence shell of the element. What is not changing as you cross a period? Answer, the inner covering electrons.

So think of it this way, the inner covering electrons are a shield against the pull of the nucleus. As you overcome a period and increase the number of protons in the cell core you increase its pull but due to the fact that you space only adding electrons come the brand-new shell the shield is not increasing but remains the same all the method across. This method the pull on the electrons being added to the valence shell is increasing steadily every the method across. What wake up if you traction harder on the electrons? Well, castle come closer to the nucleus and also the size of the atom decreases. The impact of the nucleus pulling on the electrons gift added across a duration is called the reliable nuclear charge and also is calculated as ZEff = #protons - main point # Electrons.

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



Electronegativity may be the most important of the routine properties you can learn and understand due to the fact that so plenty of other nature are count on that value. Electronegativity is an atoms ability to traction electrons towards itself.

Electronegativity is normally expressed by the Pauling Scale and also the values were determined experimentally. The table below shows the range values for the elements.


The electronegativity values boost from left to right and also bottom to top in the regular table excluding the Noble gases. The many electronegative element is Fluorine.

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


Ionization Energy

Ionization power is the quantity of energy required to remove an electron native an atom. Every ionization energies are hopeful values because every one of these removals (even those for aspects that kind positive ions) require input that energy. The more electronegative the element, the higher the ionization eneregy.

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Electron Affinity

The Electron Affinity the an element is the quantity of power gained or released through the addition of one electron. The electronegativity and also Electron Affinity boosts in the same pattern in the routine table. Left to right and also bottom to top.