another GChem question:

[blinktonheim]

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Which has the largest radius:

Ca++

K+

Ar

Cl-

S2-

according to the GRE practice book only 55% of the people answered this correctly...

thanks

 

[RCT PC CRN]

S2-

 

[luv8724]

Which has the largest radius:

Ca++

K+

Ar

Cl-

S2-

according to the GRE practice book only 55% of the people answered this correctly...

thanks

So... this is an example of isoelectric series... as you can see...

all 5 of them has same orbital configurations? (is tht how we say it?)

and in this case, atom with the most positive charge has the smallest

radius cuz it draws in electron more closely to the nucleus..

so... S2- would be the largest

 

[blinktonheim]

yup S2- it is... so for an isoelectronic series like that you dont follow the general radius trend increasing going down and to the left on the periodic table?

 

[CANgnome]

it gets screwy if it is not an isoelectric series, but for isoelectric series, they all have the same number of electrons, but different amount of protons. so, the one with fewest protons, and so lowest atomic number, is the largest. Usually happens to be the one with most (-) charge

 

[luv8724]

I guess it doesnt follow the trend....

it's just one with the highest # of proton can pack electrons more dense

 

[UCB05]

you can logically reason that the more electrons there are than protons, the larger the radius, as there are proportionately fewer protons tethering down electrons than there are electrons repelling each other. The question already makes it easy for you because the five in question are isoelectronic. The answer is the one with the fewest protons pulling in its electrons.