 Giant ionic lattices also have exceptionally high melting points. This is because the electrostatic interactions between the ions are very strong. You may notice that the magnesium 2-plus ions and oxide 2-minus ions have doubled the number of charges on their ions than the sodium and chloride ions and sodium chloride. And so magnesium oxide is held together by stronger ionic bonds. Giant ionic lattices, when in the solid state, do not conduct electricity because their ions are fixed in the lattice. This lattice structure is lost when the solid is melted, freeing up ions which can then conduct electricity. Why might magnesium oxide be a very useful high-temperature electrical insulator? Pause the video and think about this. Continue when you're ready. The answer is that magnesium oxide has a very high melting point so it retains its ionic lattice structure at a high temperature. This means that its ions are unable to conduct electricity and so makes a very good insulator. Did you get it right? The final giant structures we will consider in this video are metals. These all share the same structure whereby electrons in the outer shells or the metal atoms are free to move. The metallic bond is a force of attraction between these free electrons and the positively charged metal ions. For more information about this, please see the video titled How Atoms Bond. Metallic bonds are strong so metals retain a regular structure and usually have high melting and boiling points. Metals also have common properties. They conduct heat and electricity because of the free electron's ability to move. Free electrons also allow the metal ions to slide past one another and so metals can be hammered into shapes. This is called malleability.