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Me02 Alkali metals 2: Differences in malleability
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(For
experienced chemistry teachers only!
* Small lumps of lithium,
sodium and potassium are held by tweezers and squeezed by a knife.
* Observation
left:By
pressing on a small lump of potassium a metal sheet is obtained.
* No photo: Sodium
needs more pressure and lithium can only be scratched or cut.
* Explanation
(middle
and right): A bead model shows a lattice
of the smallest metal particles. Lithium, sodium and potassium have a similar
structure (= metallic bonding):
Atoms of the first group of the periodic system of elements release one
electron into the gaps between the resulting positive metal ions. Their
bonding is achieved by the joint attraction of this regular array of positive
ions to a "sea" of electrons which has an unlike charge.
The atomic and ionic radii
of alkali metals increase from Li < Na < K < .... So the attraction
of the positive nuclei on the negative electrons
decrease. So potassium shows the best malleability as it has the weakest
bonding.