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Why is diamond stronger than metals?

  1. Mar 2, 2016 #1

    TT0

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    I know the reasons that diamonds are stronger than covalent materials and ionic compounds. The former is weaker because there are intermolecular forces and the latter is weaker because if pressure is applied like charged ions would be forced together making it brittle. However, I cannot think why metal substances are weaker than diamonds other than that metallic bonding is a weak bond. Can someone explain this to me?

    I think that ionic bonds are as strong as covalent bonds, is this true?
     
  2. jcsd
  3. Mar 2, 2016 #2

    DrDu

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    The covalent bond in diamond is not only strong but also directed while the cohesive forces in metals and ionic compounds depend little on the relative positions of the atoms.
     
  4. Mar 2, 2016 #3

    TT0

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    Could you explain a bit more about the relative positions? and also about the direction? cheers!
     
  5. Mar 2, 2016 #4

    Borek

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    "Strong" is a rather dangerous word to be used here. Diamonds are hard, bur relatively brittle. You can scratch any metal with a diamond, but diamond hit with a hammer will break.
     
  6. Mar 2, 2016 #5

    TT0

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    I see, I meant hard. Apologies
     
  7. Mar 2, 2016 #6

    DrDu

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    In diamond, each carbon atom is surrounded tetrahedrally by other carbon atoms. If you try to move an atom keeping its distance from its bond partner constant, this would greatly weaken the bond and requires therefore a strong force. In contrast to this, in metals the ionic cores are embedded into the electron gas formed by the valence electrons like raisins in honey. Moving the ions sidewards will therefore cost little energy. Therefore metals are much more ductile than diamond. However, this is not true for transition metals, as the d-orbitals also form directed bonds. Hence metals like Tungsten are very hard and brittle, too.
     
  8. Mar 2, 2016 #7

    TT0

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    I see thank you. That was a very clear explanation :smile::smile::smile::smile::smile:
     
  9. Mar 2, 2016 #8

    DrDu

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    You are welcome!
     
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