Chapter 2: Is Matter Around Us Pure?

Elements & Compounds

Pure substances are classified into elements and compounds.

Elements

An element is a basic form of matter that cannot be broken down into simpler substances by chemical reactions.

Types of Elements - Table

TypePropertiesExamples
MetalsLustrous, conduct heat/electricity, ductile, malleableGold, Silver, Iron
Non-metalsVariety of colours, poor conductorsHydrogen, Oxygen, Carbon
MetalloidsProperties between metals and non-metalsBoron, Silicon

Quick Facts:

  • 📊 Total elements: 118+
  • 💧 Liquid at room temp: Mercury, Bromine

Compounds

A compound is formed when two or more elements chemically combine in a fixed proportion.

Iron + Sulphur Experiment Diagram:

    MIXTURE (Iron + Sulphur)              COMPOUND (FeS)
    ┌─────────────────┐                  ┌─────────────────┐
    │  ● ○ ● ○ ● ○    │      HEAT       │  ◎ ◎ ◎ ◎ ◎ ◎   │
    │  ○ ● ○ ● ○ ●    │    ───→→        │  ◎ ◎ ◎ ◎ ◎ ◎   │
    │  ● = Iron       │                  │  ◎ = Iron       │
    │  ○ = Sulphur    │                  │      Sulphide   │
    └─────────────────┘                  └─────────────────┘
    
    • Can separate with magnet           • Cannot separate with magnet
    • Gives H₂ with acid                 • Gives H₂S (rotten egg smell)
    • Variable composition               • Fixed composition (FeS)

Classification of Matter - Complete Diagram

📝 This diagram is MUST for exams!

                         MATTER
                           │
           ┌───────────────┴───────────────┐
           │                               │
     PURE SUBSTANCES                   MIXTURES
           │                               │
     ┌─────┴─────┐               ┌─────────┴─────────┐
     │           │               │                   │
  ELEMENTS   COMPOUNDS      HOMOGENEOUS        HETEROGENEOUS
     │           │           (Solutions)        (Suspensions,
     │           │                               Colloids)
  ┌──┴──┬───────┐            
  │     │       │            
Metals Non-    Metalloids   
      metals

Easy to Remember:

  • Elements → All same atoms (Na, Fe, O₂)
  • Compounds → Different atoms joined (H₂O, NaCl, CO₂)
  • Mixtures → Just mixed, not joined (salt water, air)

Comparison Table for Exam

PropertyMixtureCompound
FormationPhysical mixingChemical reaction
CompositionVariableFixed
PropertiesOf constituentsCompletely new
SeparationPhysical methodsChemical reactions

📝 Learn this table for 2-3 mark questions!