Metals and Non-metals

Overview

Metals and Non-metals is a foundational chemistry topic that appears consistently in Assam TET Paper II. This chapter tests your understanding of how elements are classified based on their physical and chemical properties, and how they behave in chemical reactions. The topic bridges basic chemistry with real-world applications—from the iron used in construction to the oxygen we breathe.

For Assam TET, expect questions on distinguishing properties of metals and non-metals, their reactions with oxygen, water, acids and bases, the reactivity series, and corrosion. Understanding this topic also helps with related areas like acids-bases-salts and environmental science. Focus on memorising key properties, the reactivity series order, and being able to predict simple reaction outcomes.

Key Concepts

• **Metals** are elements that are generally lustrous, malleable, ductile, good conductors of heat and electricity, and have high melting points. Examples: iron, copper, aluminium, gold, sodium.

• **Non-metals** are elements that are generally dull, brittle, poor conductors (except graphite), and have low melting points. Examples: carbon, sulphur, oxygen, nitrogen, phosphorus.

• **Metalloids** (semi-metals) show properties of both metals and non-metals. Examples: silicon, germanium, arsenic. These are often asked as exceptions.

• **Reactivity Series** is the arrangement of metals in decreasing order of their reactivity. A more reactive metal can displace a less reactive metal from its salt solution.

• **Ionic compounds** are formed when metals react with non-metals—metals lose electrons to form positive ions (cations), non-metals gain electrons to form negative ions (anions).

• **Corrosion** is the slow destruction of metals by chemical reaction with the environment. Rusting of iron (forming Fe₂O₃·xH₂O) is the most common example.

• **Alloys** are homogeneous mixtures of metals (or metal with non-metal) made to improve properties. Examples: brass (copper + zinc), bronze (copper + tin), steel (iron + carbon).

Formulas / Key Facts

**Physical Properties Comparison:**

| Property | Metals | Non-metals | |----------|--------|------------| | Lustre | Shiny | Dull (except iodine, graphite) | | Hardness | Generally hard | Generally soft (except diamond) | | Malleability | Can be beaten into sheets | Brittle | | Ductility | Can be drawn into wires | Cannot | | Conductivity | Good conductors | Poor conductors (graphite is exception) | | Sonorous | Produce sound when struck | Do not | | State at room temperature | Solid (except mercury) | Solid, liquid or gas |

**Reactivity Series (decreasing order):** K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au

*Memory aid: King Sona Ca(n) Manage A Zoo; Iron Leads Horses Carefully Holding Silver Gold*

**Key Chemical Reactions:**

1. **Metal + Oxygen → Metal Oxide (basic)**

• 4Na + O₂ → 2Na₂O
• 2Mg + O₂ → 2MgO

2. **Non-metal + Oxygen → Non-metal Oxide (acidic)**

• C + O₂ → CO₂
• S + O₂ → SO₂

3. **Metal + Water → Metal Hydroxide + Hydrogen**

• 2Na + 2H₂O → 2NaOH + H₂
• Ca + 2H₂O → Ca(OH)₂ + H₂

4. **Metal + Dilute Acid → Salt + Hydrogen**

• Zn + H₂SO₄ → ZnSO₄ + H₂
• Fe + 2HCl → FeCl₂ + H₂

5. **Displacement Reaction:**

• Zn + CuSO₄ → ZnSO₄ + Cu (Zn is more reactive than Cu)

**Important Exceptions to Remember:**

• Mercury is a liquid metal at room temperature
• Sodium and potassium are soft metals, can be cut with a knife
• Graphite (carbon) conducts electricity though it is a non-metal
• Diamond (carbon) is the hardest natural substance though carbon is a non-metal
• Iodine is a lustrous non-metal

Worked Examples

**Example 1:** Why does sodium react vigorously with water while iron does not?

*Solution:*

• Step 1: Check positions in reactivity series—Sodium (Na) is above Iron (Fe)
• Step 2: More reactive metals react more vigorously with water
• Step 3: Sodium is highly reactive, reacts violently with cold water producing NaOH and H₂ with heat
• Step 4: Iron is less reactive, reacts only with steam (not cold water) to form Fe₃O₄ and H₂
• Answer: Sodium is more reactive than iron in the reactivity series, hence reacts vigorously with water.

**Example 2:** Predict whether a reaction will occur: Copper metal placed in Zinc Sulphate solution.

*Solution:*

• Step 1: In reactivity series, Zn is above Cu (Zn is more reactive)
• Step 2: A less reactive metal cannot displace a more reactive metal from its salt
• Step 3: Copper cannot displace Zinc from ZnSO₄
• Answer: No reaction occurs.

**Example 3:** Why are food cans coated with tin and not zinc?

*Solution:*

• Step 1: Both tin and zinc can protect iron from rusting
• Step 2: Zinc is more reactive than tin and can react with food acids
• Step 3: Tin is less reactive and does not react with organic acids in food
• Answer: Tin is less reactive and safe for food contact; zinc may react with food acids and contaminate food.

Common Mistakes

• **Confusing lustre with conductivity** → Lustre means shiny appearance; conductivity refers to heat/electricity transfer. Graphite conducts electricity but is not lustrous like metals.

• **Thinking all metals are hard** → Sodium and potassium are soft metals that can be cut with a knife. Always remember these exceptions.

• **Reversing the displacement rule** → Students often think any metal can displace any other. Correction: Only a MORE reactive metal displaces a LESS reactive one from its solution.

• **Forgetting that hydrogen is in the reactivity series** → Metals above hydrogen in the series react with dilute acids to release H₂; metals below hydrogen (Cu, Ag, Au) do not react with dilute HCl or H₂SO₄.

• **Assuming all non-metal oxides are gases** → P₄O₁₀ (phosphorus pentoxide) is a solid non-metal oxide. State depends on the specific compound, not just the category.

Quick Reference

• Metals form basic oxides; non-metals form acidic oxides
• Reactivity series: K, Na, Ca, Mg, Al, Zn, Fe, Pb, H, Cu, Hg, Ag, Au
• Mercury is the only liquid metal; bromine is the only liquid non-metal
• Rusting needs both oxygen and moisture; prevention methods include painting, oiling, galvanising, electroplating
• Gold and silver are least reactive (found in native/free state)
• Copper turns green due to formation of basic copper carbonate (patina)