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Metallic bonding and alloys – sea of electrons, conductivity, malleability and the bonding triangle

ChemistryChemical BondingAges 17–18

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A layer of positive metal ions in a sea of delocalised electrons: apply a voltage to watch the electrons drift as a current, hammer the metal to make the layers slide without breaking, and heat Li, Na, K, Mg and Al to compare their melting points with ion charge and radius. The alloy screen adds substitutional atoms (brass, bronze, 18-carat gold, solder, duralumin, stainless steel) or interstitial carbon (steel) that distort the layers, with hardness, density and uses; a van Arkel–Ketelaar triangle places substances by electronegativity difference and mean electronegativity.

Lesson: Metallic bonding, properties of metals and alloys

What it shows

Metals are lattices of positive ions held together by their attraction to a sea of delocalised electrons. Because the electrons can move, metals conduct electricity; because the bonding has no direction, layers of ions can slide over each other, so metals are malleable and ductile. A higher ion charge and a smaller ion radius give a stronger attraction and usually a higher melting point. In an alloy, atoms of a different size distort the layers so they slide less easily, which makes the alloy harder. The bonding triangle classifies bonding from the mean and the difference of the electronegativities.

How to use

Choose a tab. In Metallic bonding, pick a Metal, move the Voltage V slider to start a current and raise the Temperature to see the metal melt; press Hammer or tap the lattice to make the layers slide. In Alloys, choose an Alloy, move the composition slider and press Hammer to compare how far the layers slide. In Bonding triangle, choose Element A and Element B, pick an Example, or tap the triangle.

Parameters you can change

  • Mode Metallic bonding, Alloys, Bonding triangle
  • Metal Lithium (Li), Sodium (Na), Potassium (K), Magnesium (Mg), Aluminium (Al)
  • Voltage V 0–0.1 V
  • Temperature 20–750 °C
  • Alloy Carbon steel (Fe + C), Stainless steel (Fe + Cr), Brass (Cu + Zn), Bronze (Cu + Sn), Gold alloy (Au + Cu + Ag), Solder (Sn + Pb), Duralumin (Al + Cu)
  • Element A Cs, K, Ba, Na, Li, Ca, Mg, Al, Zn, Fe, Cu, Si, Ag, Sn, B, P, H, C, S, I, Br, N, Cl, O, F
  • Element B Cs, K, Ba, Na, Li, Ca, Mg, Al, Zn, Fe, Cu, Si, Ag, Sn, B, P, H, C, S, I, Br, N, Cl, O, F

Questions to explore

  1. Why does a metal bend when it is hammered while a crystal of sodium chloride shatters?
  2. Why is the melting point of aluminium higher than that of sodium?
  3. Why does adding a little carbon to iron make steel much harder but also more brittle?

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