Physical Properties and Distinctions
To differentiate between metals and non-metals, we look primarily at their physical states and behaviors. Metals, such as iron, copper, and gold, are generally solid at room temperature—with the notable exception of mercury, which remains liquid. They possess a characteristic metallic luster, meaning they shine when polished. They are also malleable (can be beaten into thin sheets) and ductile (can be drawn into wires), making them indispensable for construction and electrical wiring.
Non-metals, such as oxygen, sulfur, and carbon, exhibit the opposite traits. They are typically dull in appearance, brittle when solid, and poor conductors of heat and electricity. While most exist as gases or solids, bromine is a unique non-metal that exists as a liquid at room temperature. Carbon is an outlier in the non-metal category because it exists in different allotropic forms; for instance, diamond is the hardest natural substance and conducts heat, while graphite is a good conductor of electricity.
Note: While most metals are hard, alkali metals like lithium, sodium, and potassium are so soft they can be cut with a knife. Always keep these exceptions in mind for objective-type questions.
Chemical Reactivity and the Activity Series
The chemical behavior of metals is defined by their reactivity. When metals react with oxygen, they form basic oxides. For example, magnesium burns in air to form magnesium oxide, which turns red litmus blue. Conversely, non-metals form acidic or neutral oxides when reacting with oxygen, such as sulfur dioxide, which forms sulfurous acid in water.
The Reactivity Series is an essential tool for competitive exams. It is a vertical arrangement of metals in descending order of their chemical reactivity. This series allows us to predict displacement reactions: a more reactive metal will displace a less reactive metal from its salt solution.
- Highly Reactive: Potassium (K), Sodium (Na), Calcium (Ca), Magnesium (Mg). These are usually extracted by electrolytic reduction.
- Moderately Reactive: Zinc (Zn), Iron (Fe), Lead (Pb). These are typically found as sulfides or carbonates and require reduction with carbon.
- Least Reactive: Silver (Ag), Gold (Au). These are often found in a native (free) state in nature.
Extraction Processes: Metallurgy
The extraction of metals from their ores involves several scientific steps collectively called metallurgy. The process begins with the enrichment of ore, where unwanted impurities known as gangue are removed. The specific method of extraction depends on the metal’s position in the reactivity series.
For metals at the bottom of the series, simple heating is often sufficient (roasting). For those in the middle, the ore is converted into an oxide through calcination (heating in limited air for carbonates) or roasting (heating in excess air for sulfides), followed by reduction using a reducing agent like carbon. Finally, for highly reactive metals, we utilize electrolytic refining, where the impure metal acts as the anode and a pure strip of the metal acts as the cathode in an electrolyte solution.
Corrosion and Prevention
Corrosion is the gradual destruction of metals by chemical reaction with their environment. The most common example is the rusting of iron, which requires both oxygen and moisture. If either is absent, rusting does not occur. This is why painting or oiling iron surfaces prevents corrosion by creating a barrier.
Advanced methods of protection include galvanization, which is the process of coating steel or iron with a thin layer of zinc. Zinc is more reactive than iron and acts as a “sacrificial anode,” corroding before the iron underneath is affected. Another method is alloying, where metals are mixed with other elements to enhance their properties—for example, stainless steel is an alloy of iron, nickel, and chromium, which is resistant to rust.
Important Facts and Comparisons
| Property | Metals | Non-Metals |
|---|---|---|
| Electron behavior | Lose electrons (Electropositive) | Gain/Share electrons (Electronegative) |
| Oxide Nature | Basic | Acidic/Neutral |
| Conductivity | Good conductors | Poor conductors (except graphite) |
| Physical State | Mostly solid (except Hg) | Solid, liquid, or gas |
Previous Year Question Hints
- Question: Why is sodium stored under kerosene oil? (Focus: Reactivity with air and moisture).
- Question: Which metal is used for galvanizing iron and why? (Focus: Sacrificial protection).
- Question: Identify the process used for the extraction of highly reactive metals like Aluminum. (Focus: Electrolytic reduction).
Quick Revision Summary
- Metals are malleable, ductile, and lustrous; non-metals are generally brittle and dull.
- Mercury is the only liquid metal; Bromine is the only liquid non-metal.
- Reactivity Series: Potassium is the most reactive; Gold is the least reactive.
- Roasting is used for sulfide ores; Calcination is used for carbonate ores.
- Galvanization is the coating of iron with zinc to prevent rusting.
- Alloys like stainless steel (Iron + Nickel + Chromium) are stronger and corrosion-resistant.
- Metals form basic oxides; non-metals form acidic oxides.
- Graphite is a non-metal that conducts electricity due to free electrons.
