Metalic bonding, transition metals
All metals have only a few electrons in the outer shells of their atoms. In a solid metal, the atoms are close together and the outer shells overlap. The outer electrons are free to move through the structure in a 'sea of electrons'. The electrons are not located in specific atoms, so they are called delocalised electrons. The metal atoms form positive ions, which are held together in a regular arrangement.
The delocalised electrons move around randomly between the positive ions in all directions. If a potential difference is apllied across a piece of metal. the electrons start to move in one direction. This is called an electric current.
The layers of positive ions in a metal can slide over each other if a large force is applied to a piece of metal. The ions are still held together by the sea of electrons, so the metal spreads out instead of breaking. It is malleable.