Atomic structure
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In P3–, S2–, Cl– ions, the increasing order of size is given in the list below. How to solve similar problems within seconds?
a) P3–, S2–, Cl–
b) Cl–, S2–, P3–
c) P3– , S2–, Cl–
d) S2–, P3–, Cl–
e) S2–, Cl–, P3–
(a) and (c) are the same! They are also correct.
P3–, S2– and Cl– all contain the same number of electrons, 18. They are isoelectronic.
The P nucleus only has 15 protons to hold on to these electrons, whilst S has 16 and Cl has 17, so you would expect the order as in (a) and (c) with the largest first. The more protons in the nucleus the stronger the pull on the electrons in the outer shell.
Jenkin
Risk assessment
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updated: 21 August 2003
