Chemical Elements and Their Classification

What is an Element?

• An element is a pure substance that cannot be broken down into two or more simpler substances by chemical processes.
• Example: Sugar is not an element because it can be broken down into carbon and water vapor, which are not elements.
• Water Vapor is also not an element as it is made from hydrogen and oxygen, both of which are elements.

Chemical Symbols of Elements

• Chemists use chemical symbols to represent elements.
• Each symbol usually consists of one or two letters:
  • Hydrogen: H
  • Carbon: C
  • Oxygen: O
  • Iron: Fe
  • Mercury: Hg
  • Calcium: Ca

Classifying Elements

• Elements can be classified based on different criteria:
  • Number of electrons in their outer shells.
  • Similarity of properties.

Metals

• Most metals are solid at room temperature, except for mercury (which is a liquid).
• Properties of metals include:
  • Shiny appearance
  • High melting point
  • High heat conductivity
  • Ductile: Can be drawn into wires
  • Malleable: Can be hammered into different shapes
  • Sonorous: Produce ringing sounds when struck
  • Excellent electrical conductors (used in electricity transmission).

Metalloids

• Metalloids exhibit both metallic and non-metallic properties:
  • Shiny appearance
  • All are solids
  • Brittle: Break when hammered
  • High melting point
  • Moderate electricity and heat conductors
• Silicon is an example of a metalloid.

Non-Metals

• Non-metals have a dull, non-lustrous appearance.
• Found in all three physical states at room temperature:
  • Solids: Carbon and sulfur
  • Liquid: Bromine
  • Gases: Helium and oxygen
• Properties of non-metals include:
  • Low melting and boiling points (except carbon)
  • Poor electrical and heat conductors (with a few exceptions)
  • Brittle in solid state.