The content that follows is the substance of basic yellowcomic.comistry class 26. In this lecture we continue the discussion of Quantum Numbers and their use in Electron Configurations and also the relationship of electron configuration to the regular properties the the elements.

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Electron Configuration

Electron configurations room the an overview of wherein the electron are approximately a nucleus. As we learned earlier, every neutral atom has actually a variety of electrons same to its variety of protons. What we will certainly do now is place those electrons right into an arrangement approximately the nucleus that shows their energy and also the form of the orbital in which they space located. Below is a an introduction of the species of orbitals and also how countless electrons each can contain:


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

Order the Fill

The stimulate in which electron are placed into the orbitals is based upon the order of their energy. This is described as the Aufbau principle. The lowest energy orbitals fill first. As with the quantum numbers themselves this stimulate was identified by calculation and is summary by the following chart:


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


How to write an Electron Configuration

The symbols offered for writing the electron configuration begin with the covering number (n) complied with by the kind of orbital and also finally the superscript shows how countless electrons space in the orbital.


For example:

Looking in ~ the routine table, you have the right to see that Oxygen has 8 electrons. Based on the stimulate of fill above, these 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 the ions existing a special instance of electron construction and likewise demonstrate the reason for the development of those ions in the very first place.

If you have to write the full electron configuration for one anion, then you space just including additional electrons and the configuration is merely continued.

For example, we understand that Oxygen constantly forms 2- ions once it makes an ion. This would include 2 electron to its common configuration do the brand-new configuration: O2- 1s22s22p6. Through 10 electron you should note that oxygen"s electron configuration is now specifically the exact same as Neon"s. Us talked around the truth that ions form because they can become an ext stable through the obtain or ns of electrons to end up being like the noble gases and also now you deserve to actually see just how they end up being the same.

The electron configurations for Cations are also made based upon the variety of electrons but there is a slight distinction in the way they room configured. First you need to write their typical electron configuration and then when you remove electrons you have to take them from the outermost shell. Keep in mind that this is not constantly the same way they to be added.

Here is an example of what i mean:

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

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

One other note on composing electron configurations: A short cut. As soon as writing several of the lower table configuration the total configuration deserve to be fairly long. In this cases, you deserve to use the vault noble gas to abbreviate the configuration as shown below. Friend just have to complete the configuration from where the noble gas leaves it:



As with every other topic we have covered to date there space exceptions to the bespeak of fill together well. But based on the electron construction that room generated, these exceptions are basic to understand.

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

Here room the actual configurations:


In these columns, the 4s and 3d

Practice, Practice, Practice

There are lots of quizzes top top electron configuration you can practice with located here

Orbital Diagrams

Another way to represent the bespeak of to fill for one atom is by utilizing an orbital diagram frequently referred to as "the small boxes":


The box are supplied to stand for the orbitals and also to present the electrons placed in them. The bespeak of fill is the same yet as you have the right to see from over the electron are placed singly right into the boxes before filling them through both electrons. This is referred to as Hund"s Rule: "Half fill before you complete fill" and again this preeminence was established based on energy calculations that shown that this to be the method atoms actually spread their electrons right into the orbitals.

Periodic Properties

One of the yes, really cool things about electron construction is their relationship to the routine table. Usually the periodic table was constructed so that elements with similar electron configurations would be aligned right into the same groups (columns).


Periodic Table showing last orbital filled because that each element

The regular table shown above demonstrates exactly how the construction of each facet was to adjust so that the last orbital filled is the same other than for the shell. The reason this to be done is the the configuration of an aspect gives the element its nature and comparable configurations yield comparable properties.

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

Atomic Size

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

What is not as intuitive is why the dimension decreases indigenous left to right. But again the building and construction of the electron configuration provides us the answer. What space you doing together you go across the periodic table? Answer, adding protons come the cell core and including electrons to the valence shell of the element. What is not changing as you cross a period? Answer, the inner covering electrons.

So think of the this way, the inner covering electrons room a shield against the pull of the nucleus. As you cross a duration and increase the number of protons in the cell nucleus you rise its pull but because you are only including electrons to the new shell the shield is no increasing yet remains the same all the method across. This means the pull 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, lock come closer to the nucleus and the dimension of the atom decreases. The effect of the cell nucleus pulling top top the electrons gift added throughout a period is called the effective nuclear charge and is calculated together ZEff = #protons - main point # Electrons.

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



Electronegativity might be the most vital of the routine properties you have the right to learn and understand because so many other nature are count on that value. Electronegativity is an atoms capacity to traction electrons towards itself.

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


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

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


Ionization Energy

Ionization power is the quantity of power required to eliminate an electron from an atom. Every ionization energies are hopeful values because all of these removals (even those for elements that kind positive ions) need input of energy. The an ext electronegative the element, the higher the ionization eneregy.

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Electron Affinity

The Electron Affinity that an aspect is the quantity of power gained or released v the addition of one electron. The electronegativity and Electron Affinity increases in the very same pattern in the routine table. Left to right and also bottom to top.