Notes on Elements, Compounds, and Mixtures

Key Concepts

• Elements, Compounds, and Mixtures
  • Fundamental concepts in chemistry.

Learning Objectives

• Understand the definitions and differences between:
  • Atom: A basic unit of matter.
  • Molecule: A group of two or more atoms bonded together.
  • Ion: An atom or molecule with a net electric charge due to the loss or gain of one or more electrons.

Atom, Molecule, and Giant Structure

• Atom:
  • Composed of protons, neutrons, and electrons.
• Molecule:
  • Formed when two or more atoms are chemically bonded.
• Giant Structure:
  • Consists of a vast number of atoms (millions) bonded together, can be either an element or a compound.

Elements vs Compounds

• Element:
  • A substance consisting of one type of atom.
• Compound:
  • A substance consisting of two or more different types of atoms chemically bonded together.

Mixtures

• Mixture:
  • Contains two or more different substances that are not chemically combined.
  • Examples include:
  • Mixture of two elements that exist as atoms.
  • Mixture of two compounds.
  • Mixture of two elements that exist as molecules.
  • Mixture of an element and a compound.

States of Matter

• Solid
• Liquid
• Gas

Chemical Changes vs Physical Changes

• Chemical Change:
  • New substances are formed.
  • Changes in appearance (color, energy changes such as light, heat, sound).
• Physical Change:
  • No new substances are formed.
  • Changes in state or appearance (e.g., dissolving).

Chemical Reactions

• Represents a process in which reactants are converted into products.
• Example:
  \text{Sodium (s)} + \text{Water (l)} \rightarrow \text{Sodium Hydroxide (l)} + \text{Hydrogen (g)}
  or
  2Na (s) + 2H2O (l) \rightarrow 2NaOH (l) + H2 (g)
• Law of Conservation of Mass:
  • In a chemical reaction, the number of atoms before the reaction must equal the number of atoms after the reaction (mass is conserved).