Metals tend to have 1-3 valence electrons in their outer shell, while non metals have 4-8 electrons in their outer shell. Metals are natural elements that are hard, opaque, shiny and dense. While non metals are chemical substances that are soft, transparent, non-shiny and brittle. You can also distinguish a metal from a non-metal based on its appearance: metals are Lustrous while non metals are Non-lustrous. In other words metals are shiny while non metals are usually dull or simply "not shiny". Melting and Boiling point can also help distinguish between metals and non metals: metals tend to have : very high melting and boiling point. Nonmetals have Low melting and boiling point. Metals are also good conductors of heat and electricity, while nonmetals are poor conductor of heat and electricity. And lastly, metals are malleable and are always hard except for sodium, and nonmetals are non-malleable and are soft except for diamonds.
