# atomic seize when isoelectronic

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#### Awuah29

##### Christian predent
7+ Year Member
15+ Year Member
quick question! How do you determine the seize of an atom let say you have atoms which are isoelectronic . e.g Cl- Ar, K +.
Which of the following is larger? Is the answer Cl- ?

quick question! How do you determine the seize of an atom let say you have atoms which are isoelectronic . e.g Cl- Ar, K +.
Which of the following is larger? Is the answer Cl- ?

they are all the same because they have the same electronic configuration

they are all the same because they have the same electronic configuration

ummm No. It depends on how many protons the atom has. the greater the atomic #, the greater # of protons, the smaller the radii. The more protons you have in the nucleus, the closer the electrons are drawn to the nucleus thus a smaller radius.

jb!

ummm No. It depends on how many protons the atom has. the greater the atomic #, the greater # of protons, the smaller the radii. The more protons you have in the nucleus, the closer the electrons are drawn to the nucleus thus a smaller radius.

jb!

ahh ok. hes right. been a little out of touch with chem. i knew if i was wrong someone would correct me neway. good work jb

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Do you mean atomic SIZE! HAHAHAHHAHAHAHAH

ummm No. It depends on how many protons the atom has. the greater the atomic #, the greater # of protons, the smaller the radii. The more protons you have in the nucleus, the closer the electrons are drawn to the nucleus thus a smaller radius.

jb!

I'm confused... It's my understanding that atomic radii increases as you go down the periodic table and left across the periodic table. So it seems the greater the atomic #, the larger the radius.
iono...

Do you mean atomic SIZE! HAHAHAHHAHAHAHAH

I was wondering how long this would take.

I'm confused... It's my understanding that atomic radii increases as you go down the periodic table and left across the periodic table. So it seems the greater the atomic #, the larger the radius.
iono...

that is when comparing neutral atoms that are NOT isoelectronic. If they are isoelectronic, use the method devised in my previous post.

hope that helped, jb!

jack is right

K+<AR<Cl-

QUOTE=BenignDMD;4732311]jack is right

K+<AR<Cl-[/QUOTE]

Is the ranking based on inference or is it based on published data? If it is the latter, can you give a reference?

Admittedly there is some confusion regarding the radius of argon. The Van der Waals radius for argon is listed at 188pm (en.wikipedia.org/wiki/Atomic_radii_of_the_elements_%28da... and as 191pm www.caton.org/images/chem/TableP.gif. There is some question about using these figures (Van der Walls) since in this case the atom is considered to be "unsquashed". Atoms other than noble gases are measured where their atomic radius is decreased by strong attractions. (www.chemguide.co.uk/atoms/properties/atradius.html). The ionic radius for potassium is 138pm and that of chlorine is 181pm http://environmentalchemistry.com/yogi/periodic/ionicradius.html). Using this information and the Van der Walls atomic radius for Ar, the ranking would be K+ 138pm< Cl- 181pm< Ar 188pm.

The generally accepted atomic radius (covalent radius) for Ar is 94 pm. (http://intro.chem.okstate.edu/1314F00/Lecture/Chyapter7/Lec111300...).

This would change the ranking to Ar 94pm< K+138< Cl-181pm.
Using a single reference with all the info www.chemicool.com/elements/argon.html the values are Ar 98pm< K+ 152pm< Cl- 167.

When looking at isoelectronic species, the atom with a higher nuclear charge will have a smaller stomic radius.

Z=19 for K+

Z=18 for Ar

Z=17 for Cl-

Because they all have the same number of electrons, the atomic radius is dependant on the # of protons in the nucleus. Since like attracts like, the isoelectronic species with more protons will pull its electrons closer, thus leading to a smaller atomic radius.

The DAT will only test you on atoms that are neutral or are isolectronic to one another becuase you can figure them out with only a periodic table. Don't worry about what values you found online for the atomic radii of these atoms.

The DAT will only test you on atoms that are neutral or are isolectronic to one another becuase you can figure them out with only a periodic table. Don't worry about what values you found online for the atomic radii of these atoms.

You are right! Good enough for govt. work.