Cu2+ and Cl-.
Could someone explain to me why Cl- has a larger radius?
Could someone explain to me why Cl- has a larger radius?
Which ion has a larger radius?
- Thread starter xjoohn
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It has to do with effective nuclear charge I believe. Because the copper ion has more protons in it's nucleus, it is going to more tightly pull the electrons towards the nucleus, when you have an oxidative state with fewer valence electrons, it is going to deshield the other electrons and cause them to be even more tightly bound to the nucleus. Same thing goes for the chloride ion, fewer protons means less effective pull, and if you add another valence electron, it shields its neighbors and they all feel less effective overall pull, so I believe the chloride ion will have a slightly larger radius than the chlorine atom.
EParker has got the right idea, positive ions are smaller than their parent atoms, and negative ions are significantly larger than their parent atoms.
Shielding is referring to the inner electrons blocking some of the attraction that the valence electrons feel from the nucleus. When you form a positive ion the remaining valence electrons experience less electron repulsion and a much greater pull from the nucleus (shielding decreases) than they did in the neutral atom, so the radius of the electron cloud contracts. When you form a negative ion the added valence electrons repel the existing valence electrons and the electron cloud has to expand to accommodate this extra electron repulsion (shielding increases). It is quite an odd couple of ions to compare because they are neither in the same group or close to each other in the period, but we can assume that despite the extra shell of electrons Cu2+ is much much smaller than Cu (being a 2+ ion), taking it below the radius of period 3 elements, whereas Cl- is larger.
Shielding is referring to the inner electrons blocking some of the attraction that the valence electrons feel from the nucleus. When you form a positive ion the remaining valence electrons experience less electron repulsion and a much greater pull from the nucleus (shielding decreases) than they did in the neutral atom, so the radius of the electron cloud contracts. When you form a negative ion the added valence electrons repel the existing valence electrons and the electron cloud has to expand to accommodate this extra electron repulsion (shielding increases). It is quite an odd couple of ions to compare because they are neither in the same group or close to each other in the period, but we can assume that despite the extra shell of electrons Cu2+ is much much smaller than Cu (being a 2+ ion), taking it below the radius of period 3 elements, whereas Cl- is larger.
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This is a really akward problem to solve. Usually, they at least give you same row or column. There's no way for you to know for sure unless you have some data for it. Or they expect you to guess on the basic theory of charges.
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OP just remember what is quoted above and you'll be in good shape. This is all the information pertaining to this concept you need to remember for the MCAT. Goodluck on the exam!
