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Malleability and Ductility are both properties of metals. I have learnt that lead is malleable but not ductile. However, don't these properties both arise from metallic bonds? So how can a substance be malleable but not ductile and vice versa?

PDF documents with information to help me learn would be appreciated.

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    $\begingroup$ Hmm.. While I admit all solid phase matter can be a subject of chemistry, specialized domains of science and technology have often much superior knowledge of some aspects, like metal processing. Malleability does not involve enduring tensil stress like ductility does. $\endgroup$
    – Poutnik
    Commented May 28, 2023 at 10:12
  • $\begingroup$ Those properties arise at a higher level than 'metallic bonds', having more to do with crystal structure and the energetics of point and line defects (vacancy/interstitial and dislocations). Welcome to Materials Science! $\endgroup$
    – Jon Custer
    Commented May 30, 2023 at 13:03

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Malleability and ductility are properties of the bulk structure of metals not their metallic bonds

It is easy to assume that the key properties of materials are primarily determined by their chemical bonds. But this is often a vast simplification, and especially so for metals.

And the explanation for why metals (or at least some of them) behave the way they do took a long time to work out with some major issues only being clarified in the mid 20th century.

The key to malleability and ductility (to oversimplify greatly) in found in the bulk material structure. Most metals are not single crystals but consists of many small domains of interacting crystals or imperfect crystals. Many of the properties are determined by what happens at the crystal boundaries when the material is under stress.

Again, simplifying a huge amount, in many metals, defects in the boundaries and the crystals can move around in ways that relieve stress and avoid the stress causing cracking in the bulk structure (as it does in brittle materials like glass or diamond). So malleable metals can undergo huge amounts of shape changes (eg you can beat gold into films just nm thick). Chemical bonds may break but in a limited and controlled way limited to specific small regions in the bulk compound.

This also explains why the specific properties of metals can be radically changed by adding small amounts of other compounds to create alloys: despite the small change in the material makeup, the added substances often concentrate at the crystal boundaries, highly influencing the behaviour of defects.

A good read that explains a lot of the science behind this (and many other material properties) and how we discovered them is The New Science of strong Materials by JE Gordon. in addition to being insightful it is also extremely readable and possibly the single best introduction to the subject of Materials Science (which is a kind of mongrel of chemistry, physics and engineering).

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