The structure where the outer electrons of metal atoms separate and create a 'sea of free electrons' that are delocalized and able to move through the whole structure, with the metal atoms becoming positively charged ions that are attracted to the sea of electrons
The delocalized electrons gain kinetic energy and move faster, transferring the gained energy throughout the metal, making heat transfer in metals very efficient
Metals are usually strong, not brittle, because the layers of metal ions are able to slide over each other when hit, and the metallic bonds do not break due to the delocalized electrons being free to move through the structure
Mixing two or more metals together disrupts the regular arrangement of the atoms, preventing the atoms from forming layers and making it harder for the atoms to slide over each other, resulting in the alloy being stronger than the pure metals