Metallic bonding occurs between metals only. Positive metal ions are surrounded by a sea of delocalised electrons. The ions are tightly packed and arranged in rows. There are strong electrostatic forces of attraction between the positive metal ions and negatively charged electrons. Pure metals are too soft for many uses and are often mixed with other metals to make alloys. The mixture of the metals introduces different sized metal atoms. This distorts the layers and prevents them from sliding over one another. This makes it harder for alloys to be bent and shaped like pure metals.