Metals and Non-Metals — Study Notes

Overview

Metals and non-metals form a fundamental classification in chemistry that appears regularly in Railway Group D exams. This topic tests your understanding of the physical and chemical properties that distinguish these two classes of elements, their behavior in reactions, and basic extraction processes. Expect 2–4 questions covering property identification, reactivity comparisons, corrosion, and simple metallurgy concepts.

Understanding the reactivity series is crucial—it predicts how metals react with acids, water, and other metals. Questions often present a reaction scenario and ask you to identify the correct outcome or select the most reactive metal. Metallurgy basics, including extraction methods for common metals like iron, aluminum, and copper, also appear frequently. Master the correlation between a metal's position in the reactivity series and its extraction method.

The topic connects directly to everyday applications—corrosion prevention, alloy formation, and industrial metal production—making it practical and memorable for exam preparation.

Key Concepts

• **Physical properties of metals**: Metals are lustrous (shiny), malleable (can be hammered into sheets), ductile (can be drawn into wires), good conductors of heat and electricity, have high melting and boiling points (except mercury), and produce a ringing sound when struck (sonorous). Most metals are solid at room temperature; mercury is the only liquid metal.

• **Physical properties of non-metals**: Non-metals are generally dull in appearance, brittle (break easily when stressed), non-malleable, non-ductile, poor conductors of heat and electricity (except graphite, a form of carbon), and have relatively lower melting and boiling points. Many non-metals exist as gases at room temperature (oxygen, nitrogen, chlorine) or solids (sulfur, phosphorus); bromine is the only liquid non-metal.

• **Chemical properties of metals**: Metals lose electrons to form positive ions (cations). They react with oxygen to form metal oxides which are basic in nature. Metals react with water and acids to release hydrogen gas. More reactive metals displace less reactive metals from their salt solutions.

• **Chemical properties of non-metals**: Non-metals gain electrons to form negative ions (anions). They react with oxygen to form non-metal oxides which are acidic or neutral. Non-metals generally do not react with water or dilute acids (except in special cases).

• **Reactivity series**: Metals arranged in decreasing order of reactivity: Potassium > Sodium > Calcium > Magnesium > Aluminum > Zinc > Iron > Lead > Copper > Mercury > Silver > Gold. This series predicts reaction outcomes and extraction difficulty.

• **Ionic compounds**: Formed when metals transfer electrons to non-metals. These compounds have high melting points, conduct electricity in molten or aqueous state, and are usually soluble in water.

• **Corrosion**: The gradual deterioration of metals due to reaction with moisture and atmospheric gases. Rusting of iron (formation of hydrated iron oxide) is the most common example. Prevention methods include painting, galvanization, electroplating, and alloying.

• **Metallurgy**: The science of extracting metals from their ores and refining them for use. The extraction method depends on the metal's reactivity—highly reactive metals require electrolytic reduction, moderately reactive metals use carbon reduction, and less reactive metals need simple heating.

Formulas / Key Facts

• **Metal oxide + Water → Metal hydroxide (base)**: Example: Na₂O + H₂O → 2NaOH
• **Non-metal oxide + Water → Acidic solution**: Example: SO₂ + H₂O → H₂SO₃
• **Metal + Oxygen → Metal oxide**: Example: 4Al + 3O₂ → 2Al₂O₃
• **Metal + Acid → Salt + Hydrogen gas**: Example: Zn + H₂SO₄ → ZnSO₄ + H₂↑
• **More reactive metal + Salt of less reactive metal → Displacement occurs**: Example: Zn + CuSO₄ → ZnSO₄ + Cu
• **Rusting equation**: 4Fe + 3O₂ + 2xH₂O → 2Fe₂O₃·xH₂O (hydrated ferric oxide)
• **Anodizing**: Process of forming a protective oxide layer on aluminum by making it the anode in electrolysis
• **Galvanization**: Coating iron with a thin layer of zinc to prevent rusting
• **Amphoteric oxides**: Metal oxides that show both acidic and basic properties (Al₂O₃, ZnO, PbO)
• **Aqua regia**: Mixture of concentrated HCl and HNO₃ in 3:1 ratio; can dissolve gold and platinum
• **Thermit reaction**: Fe₂O₃ + 2Al → 2Fe + Al₂O₃ + Heat (used in welding railway tracks)

Worked Examples

**Example 1: Identifying reactivity from displacement**

*Question*: Metal X displaces metal Y from its salt solution, but metal Y displaces metal Z. What is the correct order of reactivity?

*Solution*:

• Step 1: X displaces Y means X is more reactive than Y
• Step 2: Y displaces Z means Y is more reactive than Z
• Step 3: By transitive property, X > Y > Z
• **Answer**: X is most reactive, Z is least reactive

**Example 2: Predicting reaction outcome**

*Question*: Will copper react with dilute hydrochloric acid? Why?

*Solution*:

• Step 1: Check copper's position in reactivity series—it is below hydrogen
• Step 2: Only metals above hydrogen in the series can displace hydrogen from acids
• Step 3: Copper cannot displace hydrogen
• **Answer**: No, copper will not react with dilute HCl because it is less reactive than hydrogen

**Example 3: Choosing extraction method**

*Question*: Why is aluminum extracted by electrolytic reduction and not by heating with carbon?

*Solution*:

• Step 1: Aluminum is highly reactive (above carbon in reactivity series)
• Step 2: Carbon cannot reduce oxides of metals more reactive than itself
• Step 3: High reactivity metals have strong metal-oxygen bonds requiring electrical energy to break
• **Answer**: Aluminum is too reactive for carbon reduction; electrolysis of molten aluminum oxide is necessary

Common Mistakes

• **Confusing malleability with ductility**: Malleability is hammering into sheets; ductility is drawing into wires. Both are metal properties, but they describe different behaviors. Remember: malleable = sheets, ductile = wires.

• **Assuming all metals react with water**: Only highly reactive metals (K, Na, Ca) react vigorously with cold water. Magnesium reacts with hot water, and aluminum/zinc react with steam. Less reactive metals don't react with water at all.

• **Thinking non-metal oxides are basic**: Most students memorize "metal oxides are basic" but forget non-metal oxides are acidic or neutral. CO₂, SO₂, NO₂ form acids with water; CO is neutral.

• **Mixing up galvanization and electroplating**: Galvanization specifically means zinc coating (usually by dipping in molten zinc). Electroplating is a broader term using electrolysis to coat with any metal (chromium, nickel, silver, etc.).

• **Believing reactivity series applies to all reactions**: The series primarily predicts reactions with water, acids, and displacement reactions. It doesn't directly predict reaction rates with oxygen or other specific reactions—those depend on additional factors like surface area and temperature.

Quick Reference

• Metals: lustrous, malleable, ductile, conduct electricity, form cations, react with acids to give H₂
• Non-metals: dull, brittle, insulators (except graphite), form anions, oxides are acidic
• Reactivity series (top 5): K > Na > Ca > Mg > Al
• Extraction: Highly reactive (electrolysis), moderately reactive (carbon reduction), less reactive (heating)
• Rusting requires oxygen and moisture; prevented by galvanization, painting, or alloying
• Amphoteric oxides (ZnO, Al₂O₃) react with both acids and bases