MediumChemistryHigh School (11–12)The d- and f-Block Elements › Transition Elements (d-Block)NumericalA-LevelBoard ExamIB
The metallic radii of the first series are Sc 164 pm, Cr 129 pm and Ni 125 pm…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
The metallic radii of the first series are Sc , Cr and Ni . Find the mean fall in radius per element from scandium to chromium (three steps), and from chromium to nickel (four steps). Compare the two.
Need a reminder? The key ideaShow
The nuclear charge rises by one at each step of a series, but a new electron screens the electrons by about , so rises slowly. Metal bonds are strong where many d electrons can bond. Enthalpy of atomisation, , is the energy to turn one mole of solid metal into gaseous atoms. The energy to reach is , and hydration returns part of it.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. Scandium to chromium. The radius falls by in steps, which is per step.
Step 2. Chromium to nickel. The radius falls by in steps, which is per step.
Step 3. Compare. The first half of the series shrinks about twelve times faster.
Answer: per step, then per step.
Why. In the first half, the nuclear charge wins. In the second half, the repulsion between the many d electrons almost cancels the extra pull.
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