Summary
Highlights
Most elements are metals, located on the bottom left of the periodic table. Metals typically form positive ions by losing outer electrons, whereas non-metals either don't form ions or form negative ions. This behavior is due to their electron shell configuration; atoms aim for a full outer shell for stability. Metals on the left have few outer electrons, making it easy to lose them and form positive ions. Non-metals, with many outer electrons, would require too much energy to lose them, thus forming negative ions by gaining electrons.
Metals become more reactive down a group because elements with more shells have outer electrons further from the nucleus. This weaker nuclear attraction means these electrons are lost more easily, making the metal more reactive. Metals exhibit metallic bonding, which explains their strength, malleability (bendable without breaking), high conductivity of heat and electricity, and generally high melting and boiling points. They are also shiny and sonorous (produce a ringing sound).
Non-metals, in contrast, tend to be dull, brittle (easily broken), and have low melting and boiling points, with many being gases at room temperature. They are poor conductors of electricity and generally have lower densities than metals.
Transition metals, located in the center of the periodic table, possess all typical metallic properties. Additionally, they can form multiple types of positive ions (e.g., chromium 2+, 3+, 6+), which often result in colored compounds. A key practical feature is their ability to act as excellent catalysts, substances that increase reaction rates without being consumed, as seen with iron in the Haber process and nickel in alkene hydrogenation.