3A+Grace+Lee

__ What is atomic radii? __
== Atomic radii, which is also known as atomic radius is a term that refers to thedistance between the atoms from the nuclei. In order to calculate the radius of an atom, two atoms are needed where the distance between the nuclei are measured and then dividing the distance by two.==

== The left diagram, the atoms are pulled closely together, therefore their radius will be less than if they are just touching (the right diagram). This occurs with metal atoms in a metallic structure or atoms covalently bonded to each other. This is called the metallic radius or the covalent radius depending on the bonding. ==

__ Trends __
== 2 trends can be found in the periodic table. One trend can be found by moving from left to right across the periodic table where the electrons are added one at a time to the outer shell. The protons, which are found in the nuclei, are able to attract the electrons towards it as more protons are added to the nuclei therefore the atomic radius decreases. However, this trend only applies excluding the noble gases such as Neon and Argon as they are not able to form bonds. The other trend can be found by going down the periodi c table vertically. As you go down, instead of adding electrons at a time, a new outer shell is added therefore the outer electrons become further apart from the nuclei. This causes the atomic radius to increase.==

==The following diagram is a periodic table showing the picometers (pm) of each element. As it is explained above, noble gases are excluded for the trend that is found moving across the periodic table and the atomic radius decreasing. Also within this diagram, you are able to see the atomic radius is increasing as you go down the table vertically.==

[[image:Screen_shot_2012-02-16_at_9.15.43_PM.png width="249" height="235" align="left"]]__ Sodium __
== The innermost shell (closest shell to the nuclei) is called the K shell. The maximum number of electron that can exist in this shell is two. As you can see in diagram on the right, you will find only two electrons present on the innermost shell. The next shell is called the L shell. The L shell and M shell, the maximum number electron that can exist in each shell is eight. You will find in the diagram that there is only one electron that is present on the outer shell. ==

element, which is in the same group as sodium.
== The same system of the electron shell also applies for potassium. K shell can only contain 2 electrons and L and M can contain maximum of 8 each. You will find in the diagram that there is an extra layer of shell (called as the N shell). The theory mentioned previously states that as you go vertically down the table, the atomic radii increases due to another layer of electron shell being added. As you can see in the diagram on the right, the layer has been added therefore is further away from the nuclei. ==

Magnesium is the 12th element, which is in the same period as sodium.
== The same system of the electron shell also applies for potassium. K shell can only contain 2 electrons and L and M can contain maximum of 8. You will find in the diagram that there is an extra electron on the outer shell. The theory mentioned previously states that as you go down the periodic table horizontally, the atomic radii decreases due to number of protons increasing. ==

__ Conclusion __
== The examples above hopefully have contributed to your understanding. Therefore, the atomic radii trend that can be found in the periodic table is the radius decreasing when you go down the table horizontally and the radius increasing when you go down the table vertically. ==