3AT1Andrew

**__Atomic Radii __** **__By __** **__Andrew Borthwick-Clarke __**
 * __Task 1 __**

The periodic table of elements is one of the most important documents for scientists worldwide. The periodic table gives scientists information including: The worldwide accepted name, atomic number, symbol and atomic mass, for each and every element so far known to man. Within the periodic table there are a number of trends occurring that can be related to the properties of the elements. One trend that will be discussed in more detail below is the atomic radii.
 * Introduction: **

The atomic radius or radii of a element is a measure of the size of the atom. It is usually measured by determining the distance between the nucleus and the boundary of the surrounding electron cloud. It can also be found by measuring the distance between the nuclei of two covalently bonded atoms and dividing this distance by two
 * What is it: **

media type="file" key="Periodic Trends in Atomic Radius [SaveYouTube.com].mp4" width="376" height="376" align="center"

The force of attraction between the nucleus and the electrons in the outer shells begins to decrease the further away they are situated from each other. People assume that the bigger the atomic mass, the bigger the atomic radii is, although this statement is true for the “groups”( going down) this is not true for the “periods” (moving left to right on the periodic table).



To view a bigger periodic table visit: :[]
Looking at the elements in group two (Be, Mg, Ca, Sr, Ba, Ra), From the above picture of the periodic table we can see that the masses and atomic numbers are increasing. Below is a table that shows the atomic radius of group two:
 * Trends in periodic table “groups”: **

As we can see from the above table and graph, the further we move down the group, the bigger the mass and the atomic radii becomes. The reason why this occurs is due to the number of electrons within each element. The increase in the number of electrons means that there are more electron shells surrounding the nucleus. This increase in shells causes the attraction forces between the nucleus and the far most electrons to decrease and the atomic radii to increase, the decrease in attraction makes the element more reactive with other elements.

Beryllium which is at the start of group two has an atomic number of 4, and a atomic mass of 9.012. When we compare this to Radium (which is further down the group) which has an atomic number of 88 and a atomic mass of 226, we are able to see the trend that was discussed above between the atomic radii and number of electron shells below: <span style="font-family: 'Arial','sans-serif'; font-size: 18.6667px;">

<span style="font-family: 'Arial','sans-serif'; font-size: 18.6667px;">The distance between Radium and its far-most electron has a far greater distance compared to that of Beryllium, simply due to the large difference in electron shells.

<span style="font-family: 'Arial','sans-serif'; font-size: 18.6667px;">Watch the video below to discuss the trends in groups (For group 1)

media type="custom" key="12497292" width="350" height="350" align="left"

<span style="font-family: 'Arial','sans-serif'; font-size: 18.6667px;">The effective nuclear charge is the attractive forces between the protons in the nucleus and the electrons after the repulsive forces of the atoms electrons are factored out.
 * __<span style="font-family: 'Arial','sans-serif'; font-size: 18.6667px;">Effective nuclear charge: __**

<span style="font-family: 'Arial','sans-serif'; font-size: 18.6667px;">Unlike that of groups, when looking at the atomic radius in the periods, we see that the atomic radius decreases. <span style="font-family: 'Arial','sans-serif'; font-size: 18.6667px;">The table and graph below show the atomic radiuses for period three:
 * __<span style="font-family: 'Arial','sans-serif'; font-size: 18.6667px;">Trends in the Periodic table “periods”: __**

<span style="font-family: 'Arial','sans-serif'; font-size: 18.6667px;">When comparing the above table and graph, to the picture of the periodic table (near the beginning) we can see that the trend that occurs in the groups is not the same. In fact when we move from left to right (excluding the last column, Noble gases) we are able to see that when the mass number increase, the atomic radius decreases. The reason behind why this is occurring is due to the effective nuclear charge acting upon the electrons in the period. The further right the element is, the more attraction force there is between the nucleus and the electrons. <span style="font-family: 'Arial','sans-serif'; font-size: 18.6667px;">This stronger attraction between them “pulls” the electrons a little closer to the nucleus, which in return decreases the atomic radius and decreases the reactivity of the elements. <span style="font-family: 'Arial','sans-serif'; font-size: 18.6667px;">The picture below shows the attraction forces between the nucleus and the electrons for period 3 (left to right)




 * __<span style="font-family: 'Arial','sans-serif'; font-size: 18.6667px;">Summing it up: __**
 * <span style="font-family: 'Arial','sans-serif'; font-size: 18.6667px;">When looking at the “groups”, the further down the column, the larger the mass becomes, and so too the atomic radius.
 * <span style="font-family: 'Arial','sans-serif'; font-size: 18.6667px;">When looking at the “periods”, the further right in the row the element is the more attraction forces there are, which in return decrease the atomic radius.

<span style="font-family: 'Arial','sans-serif'; font-size: 16px;">http://www.creative-chemistry.org.uk/alevel/module1/trends5.htm <span style="font-family: 'Arial','sans-serif'; font-size: 16px;">http://www.creative-chemistry.org.uk/alevel/module1/trends1.htm
 * __<span style="font-family: 'Arial','sans-serif'; font-size: 18.6667px;">For more information visit: __**

http://www.crystalmaker.com/support/tutorials/crystalmaker/atomicradii/index.html http://www.webelements.com/periodicity/eff_nuc_charge_clementi_3s/period_3sp.html http://en.wikipedia.org/wiki/Atomic_radius Graphs and tables from: http://www.creative-chemistry.org.uk/alevel/module1/trends5.htm http://www.creative-chemistry.org.uk/alevel/module1/trends1.htm
 * __<span style="font-family: 'Arial','sans-serif'; font-size: 18.6667px;">Bibliography: __**