Why the Division Matters

The metal-nonmetal divide predicts real-world chemistry:

• Metal + nonmetal usually forms an ionic compound (table salt: sodium metal + chlorine gas)
• Nonmetal + nonmetal usually forms a covalent compound (water: hydrogen + oxygen sharing electrons)
• Metal + metal forms an alloy (bronze: copper + tin melted together)
• Metalloids serve as semiconductors because their conductivity can be precisely tuned with doping — adding tiny impurities
• Reactivity increases as you move left and down for metals (cesium explodes in water) and up and right for nonmetals (fluorine reacts with almost anything)