• Pharmacy Job Market Webinar

    Are you considering applying to pharmacy school but are concerned about job prospects when you graduate? Join us on Wednesday, July 28th at 8 PM Eastern to hear from three PharmDs about their experiences and options outside of retail pharmacy.

Awuah29

Christian predent
7+ Year Member
15+ Year Member
Oct 13, 2003
294
0
New Jersey
Status (Visible)
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- ?
 
B

BodybldgDoc

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
 
J

jackbauer!

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.

(smallest radius) K+ < Ar < Cl- (largest radius)

hope that made sense.

jb!:)
 
B

BodybldgDoc

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.

(smallest radius) K+ < Ar < Cl- (largest radius)

hope that made sense.

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
 
About the Ads

mshopeful

Full Member
10+ Year Member
7+ Year Member
Oct 12, 2006
86
0
Status (Visible)
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.

(smallest radius) K+ < Ar < Cl- (largest radius)

hope that made sense.

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...
 
J

jackbauer!

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!:)
 

doc toothache

Full Member
15+ Year Member
Jan 17, 2006
8,385
2,654
Status (Visible)
  1. Dentist
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.
 

BenignDMD

Full Member
10+ Year Member
Mar 28, 2005
248
2
Status (Visible)
  1. Resident [Any Field]
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.
 

doc toothache

Full Member
15+ Year Member
Jan 17, 2006
8,385
2,654
Status (Visible)
  1. Dentist
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.
 
This thread is more than 14 years old.

Your message may be considered spam for the following reasons:

  1. Your new thread title is very short, and likely is unhelpful.
  2. Your reply is very short and likely does not add anything to the thread.
  3. Your reply is very long and likely does not add anything to the thread.
  4. It is very likely that it does not need any further discussion and thus bumping it serves no purpose.
  5. Your message is mostly quotes or spoilers.
  6. Your reply has occurred very quickly after a previous reply and likely does not add anything to the thread.
  7. This thread is locked.