Basics of Chemistry: Elements, Atoms, and Compounds

Introduction

• Lecturer: Bhavika, Chemistry Mentor
• Platform: PW English
• Objective: Strengthen foundational knowledge in chemistry for a strong career
• Topic of Lecture: Elements, Atoms, and Compounds

Key Concepts

Atom

• Definition: A single entity containing a nucleus (protons and neutrons) with electrons moving around it.
• Characteristics:
  • Consists of a nucleus with protons and neutrons
  • Electrons orbit the nucleus

Molecule

• Definition: Consists of two or more atoms (same or different).
• Examples:
  • Same atoms: H₂, O₂
  • Different atoms: HCl, H₂O, NH₃

Matter

• Definition: Anything that has mass and occupies space.
• Categories:
  • Pure Substance: Made up of only one type of substance.
    • Examples: Pure milk, pure oil (everyday usage different from chemistry context)
  • Mixture: Made up of more than one type of substance.
    • Examples: Air, lemonade

Classification of Pure Substances

• Element: Molecules consisting of the same type of atom.
  • Examples: H₂, O₂, N₂, O₃, S₈
• Compound: Molecules consisting of different types of atoms.
  • Examples: HCl, H₂O, NH₃

Differences Between Compounds and Mixtures

• Compound:
  • Consists of atoms in definite composition
  • Can be separated by chemical reactions
  • Properties different from constituent elements
  • Example: Na (reactive metal) + Cl₂ (poisonous gas) → NaCl (common salt)
• Mixture:
  • Variable composition, no new compound formed
  • Can be separated by physical methods
  • Constituents retain original properties
  • Example: Salt water

Types of Mixtures

• Homogeneous Mixture: Uniform composition (e.g., lemonade)
• Heterogeneous Mixture: Non-uniform composition (e.g., sand and water)

History and Definitions

• Robert Boyle: First scientist to use the term 'element'
• Antoine Lavoisier: Provided useful definition of an element as a basic form of matter that cannot be broken down by chemical reactions

Classification of Elements

• Metals, Non-Metals, Metalloids
• Element Characteristics:
  • Formed from the same type of atom
  • Simplest form, cannot be broken down further

Pictorial Representations

• Element: Wall made of same-colored bricks (atoms)
• Compound: Wall made of different-colored bricks (atoms of different types)
• Mixture: Wall with bricks of various colors (variable composition)

Conclusion

• Q&A: Students encouraged to ask questions in the comments
• Next Steps: Further lectures to build on this foundational knowledge
• Closing Remarks: Stay positive, keep smiling, and take care