3a+Scott




 * What is it: ** Atomic Radii or (radius) is defined as the radius of an element and generally increases when an element has more mass or more shells of electrons. There are certain trends in the periodic table which can be related to the different sized atomic radius between elements.

The attraction force between the electrons in the shells and the nucleus of an atom is also varying with the atomic radius. As an atom has more mass then its radius is bigger as-well, this can lead us to think that the attraction force between the electrons of the outer shell and the nucleus weakens as well. Therefore, if an atom has a bigger atomic radius then its more reactive because of the bonds being weaker, due to the distance between the electrons and the nucleus and this is how we can identify any trends in the periodic table. When we go down each group of the periodic table we can identify how the atomic radius increases because a new energy level is added to the element.

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As seen in-group 1 of the periodic table the atomic number and the mass number both increase as you go down the group. As seen in the image to the left of screen as the mass increases as we go down the group, this can lead us to think that the Atomic radius must as increase as-well, because the bigger the atom the bigger its radius must be. This is the first recognised trend of Atomic radii in the periodic table- an increase of mass going down the group means and increased atomic radius also. http://www.creative-chemistry.org.uk/alevel/module1/trends1.htm#table

Lithium is at the top of group 1, it has a mass number of 6.94 and an atomic number of 3. We can compare this element to another further down the group.We can prove the theory that the Atomic radius will increase as we go down the group because if an atom has more mass (a bigger atomic radius) it must be more reactive, because the radius increases and so the outer shell gets further away from the nucleus.

As there is only 3 electrons in the shell this means that the bond of this atom with its shell is very strong this is why Lithium isn’t very reactive with water when compared to other atoms lower down in group 1, it wont give up its electrons easily for a reaction to take place. By looking at the reactivity of an element in group 1 it can help us identify the trend of increasing atomic radius.


 * In comparison we have Caesium reacting with water **

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 Caesium is the 6th atom in the first group **. ** It has a mass number of 132.90 and an atomic number of 55. As it has such a high mass number there are many shells to this atom, and because of that makes it a very reactive element even with the most simplistic compounds such as water as seen in the above video. This is because of how far away the outer shell is from the nucleus and so it will give up its electrons a lot easier. To summarise a bigger atomic radius makes an element more reactive, this is a good technique to observe trends in the periodic table.

After looking at two differently structured atoms in group 1 Lithium and caesium, as we go further down the group an element has a bigger Atomic radius because it has so many more electrons in its shells and the distance from the nucleus to the outer shell is much bigger.

The graph to the right of screen shows how the atomic radius of the elements in group 1 increases as we go down the group, it proves the theory of a trend where the Atomic radius increases if a element has more mass and(or ) is more reactive going down a group of the periodic table.




 * For More information visit one of these sites.**

http://www.creative-chemistry.org.uk/alevel/module1/trends1.htm#table en.wikipedia.org/wiki/Atomic_radii