Atomic radius' of noble gases

[ash_wolf]

Heyy there!

 

I have a question about the Modern Periodic Table...

All noble gases, as we know, are placed in group 0, and it is also known that the atomic radii of elements decreases as we move from right to left across a period. This is due to the nuclear attraction and the electronegativity of the elements.

But since noble gases dont have nuclear attraction, surely their atomic radii must be bigger than the element before it! It was also stated that the noble gases have larger radii than the rest of the elements in the period....is that true in all periods??

I had got a question asking me to state the element with the largest atomic radii in period 2, so I wrote 'Neon', but the answer turned out to be 'Lithium'...that's why I'm confused

[Comandante]

Atomic radii don't decrease as you move from right to left, atomic radii generally decrease as you move across a period from LEFT to RIGHT and they increase as you go down the group.

 

The reason why atomic radii decrease as you move from left to right across a period is that the number of protons increases by 1 per each step across, this causes increased nuclear charge and attracts the outer electrons more strongly towards the center, hence decreasing the radius. The atoms with the largest atomic radii are located in Group 1 and at the bottom of groups.

 

I don't have a lot of time now but here are some sites to help; http://www.chemguide.co.uk/atoms/properties/atradius.html and this table; http://www.crystalmaker.com/support/tutorials/crystalmaker/resources/VFI_Atomic_Radii.jpg

[jdurg]

You also have to keep in mind how the measurements of atomic radii are done. With most elements, it is done in the form of some type of bonding so there is a bit of a "falsity" there. Noble gases don't even form bonds with themselves like the halogens and other covalently bonded gases do, so the radii you read in regards to noble gases are a bit misleading. You can compare a noble gas radius to another noble gas radius and have the measurements mean something, but if you compare a noble gas radius with that of any other element in its period it's a bit misleading.

 

Also, the noble gases do have nuclear attraction. ALL elements have nuclear attraction. That is part of what keeps the electrons in place. Just because an element doesn't form bonds easily, if at all, doesn't mean that they don't experience nuclear attraction.

[ash_wolf]

@Sysco

lol yeah, i meant left to right

Thanks for the sites....they cleared up the matter

 

@jdurg

Thanks a lot...yeah what you say makes sense, noble gases must be having some nuclear charge, but i guess that's not as much as the rest of the elements as this is a stable element

[insane_alien]

ash_wolf, the nuclear charge is the same as the number of protons it has.

 

there ar two major factors in how tightly the outer electrons are held (how small the radii are) the nuclear charge and shielding from lower electrons. nuclear charge increases by 1 for every Z and the shielding only takes into account the electons in lower shells.

 

so hydrogen has one electron, one proton, no shielding helium has 2 protons and electrons and no shielding. so the electrons will be held closer. than hydrogen.

 

in general a period will have the same level of shielding but varying nuclear charge. this is why noble gasses have the smaller radii