Key Concepts in Atomic Theory and Change

Development of Atomic Theory

  • All matter is composed of atoms.
  • Early concepts by Democritus (5th century BCE) theorized indivisible particles called 'atomos'.
  • Antoine and Marie-Anne Lavoisier (1780s) proposed matter cannot be created or destroyed and cataloged elements.
  • John Dalton (1810) established atomic theory, linking atoms to elements and proposing that atoms have different weights.

Periodic Table

  • Mendeleev (1869) organized 56 known elements into a periodic table based on atomic properties and predicted properties of undiscovered elements.
  • The periodic table is arranged by atomic number and grouped by chemical properties (periods: rows, groups: columns).

Atomic Structure and Elements

  • Elements consist of one type of atom and are represented in the periodic table.
  • Monatomic and Diatomic Gases: Monatomic (single atoms like Helium), Diatomic (pairs of atoms like Oxygen).
  • Atomic number correlates with an element's identity, while atomic mass relates to the number of protons and neutrons.

Molecules and Compounds

  • Molecule: Group of bonded atoms.
  • Compound: Molecule with different elements (e.g., Water - H₂O).
  • Bonded Element: Comes from a single type of atom (e.g., O₂).
  • Polymer: Long chains of repeating units (e.g., plastics).
  • Mixtures: are combinations that do not present a fixed ratio and cannot be represented by a chemical formula.

Changes in Matter

  • Physical Change: Changes in state (solid, liquid, gas) that are reversible (e.g., ice melting).
  • Chemical Change: Produces new substances and involves bond breaking and forming (e.g., burning toast). Evidence includes heat/light production, color change, gas formation.

Chemical Reactions

  • Reactants are starting substances, and Products are the outcome of reactions, depicted in chemical equations (e.g., 2H₂ + O₂ → 2H₂O).
  • Factors influencing reaction rates include temperature, concentration, surface area, and catalysts (enzymes in biological processes).

Science Application and Recycling

  • Chemistry is fundamental in creating various materials used in daily life, including pharmaceuticals, plastics, dyes, and construction materials.
  • Both physical and chemical changes are essential for recycling, helping to minimize waste by repurposing materials.