Why does iron rust into crumbling flakes while gold shines undimmed after thousands of years in a tomb? The answer lies in one simple habit: how eagerly, or reluctantly, an element gives up its electrons.
About 75% of the periodic table is metal, yet gold jewellery from a 5,000-year-old Egyptian tomb still gleams, while an iron gate left outside for a single rainy season starts to crumble into orange flakes. The difference between these two fates comes down to one habit each element either has or lacks: how easily it lets go of its outermost electrons.
Metals and non-metals are distinguished by both their physical properties and their chemical behaviour. Physically, most metals share a shiny surface, high density, and the ability to conduct heat and electricity well; they are also malleable (can be hammered into sheets) and ductile (can be drawn into wire). Non-metals, by contrast, are typically dull, poor conductors, and brittle when solid, though several exist as gases or liquids at room temperature.
| Property | Metals | Non-Metals |
|---|---|---|
| Appearance | Shiny (lustrous) | Dull |
| Conductivity | Good conductors of heat and electricity | Poor conductors (except graphite) |
| Malleability | Malleable and ductile | Brittle when solid |
| State at room temperature | Solid (except mercury) | Solid, liquid, or gas |
The deeper chemical distinction, building on the metallic and ionic bonding covered earlier in this series, comes down to electron behaviour. Metal atoms hold their outermost electrons loosely and readily give them up, forming positively charged cations, which is exactly the "sea of electrons" behaviour that gives metals their conductivity and shine. Non-metal atoms, by contrast, hold their electrons tightly and often gain additional electrons from other atoms, forming negatively charged anions.
When sodium metal reacts with chlorine gas, sodium readily loses its single outer electron to become Na⁺, while chlorine gains that electron to become Cl⁻ — the same ionic bonding process covered earlier in this series, now viewed through the lens of a metal meeting a non-metal.
Not every metal gives up its electrons with equal enthusiasm. The reactivity series ranks metals from most to least reactive, based on how readily each one loses electrons and reacts with substances like water, oxygen, and acids.
A simplified reactivity series: metals near the top react vigorously, while gold near the bottom barely reacts at all.
This ranking has real predictive power: a more reactive metal will always displace a less reactive one from a compound in a single replacement reaction, the reaction type introduced earlier in this series. It also explains why sodium and potassium must be stored away from air and water, while gold can be buried in a tomb for millennia without tarnishing.
Corrosion is the gradual destruction of a metal caused by a chemical reaction with its environment, usually oxygen and moisture in the air. The most familiar example is rusting, specifically the corrosion of iron, in which iron reacts with oxygen and water to form iron oxide, the reddish-brown, crumbly substance that weakens iron and steel structures over time.
Not every metal corrodes the same way. Aluminium actually reacts with oxygen faster than iron does, but the aluminium oxide layer that forms is thin, tough, and transparent, sealing the surface and preventing further damage underneath — which is why aluminium window frames stay looking new for decades, while an unprotected iron gate rusts through. Engineers exploit this same principle with galvanisation, coating iron or steel in a layer of zinc that corrodes first, sacrificially protecting the metal underneath.
An alloy is a mixture of two or more elements, at least one of which is a metal, blended together to improve on the properties of the pure metal alone. Alloys are typically stronger, more durable, or more corrosion-resistant than any single metal used on its own.
| Alloy | Made From | Improved Property |
|---|---|---|
| Steel | Iron + carbon | Greater strength and hardness |
| Stainless steel | Iron + chromium + nickel | Resistance to rusting |
| Bronze | Copper + tin | Greater hardness and durability |
Whether a metal shines for millennia or crumbles within a season comes down to the same simple habit explored throughout this series: how willingly an atom gives up its electrons. Gold's stubborn refusal to react is exactly why it has survived in tombs for thousands of years, while iron's eagerness to bond with oxygen is exactly why a rusted gate needs regular paint. Understanding this reactivity, and engineering around it with alloys and protective coatings, is what allows bridges, ships, and skyscrapers to stand for generations. The next article in this series turns to electrochemistry, exploring how these same electron transfers can be harnessed to generate electricity itself.
14 questions. Select an answer for each, then submit to see your score instantly.