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Chemistry 2nd Quarter

1. Introduction to Chemistry

  • Chemistry is the scientific study of matter, its properties, how it interacts with energy, and how it changes.
  • It is often called the "central science" because it connects other natural sciences like physics, biology, and geology.

2. Fundamental Concepts

2.1 Matter
  • Matter: Anything that has mass and takes up space.
  • Pure Substances:
    • Elements: Cannot be broken down into simpler substances by chemical means (e.g., Oxygen (O), Hydrogen (H), Gold (Au)). All atoms in an element have the same number of protons.
    • Compounds: Formed when two or more different elements are chemically bonded together in fixed proportions (e.g., Water (H2O), Carbon Dioxide (CO2)). Can only be separated by chemical reactions.
  • Mixtures: Physical combinations of two or more substances where each substance retains its own chemical identity.
    • Homogeneous Mixtures (Solutions): Uniform composition throughout (e.g., saltwater, air).
    • Heterogeneous Mixtures: Non-uniform composition; components are visibly distinguishable (e.g., sand and water, oil and water).
2.2 Atoms
  • Atom: The smallest unit of an element that retains the chemical identity of that element.
  • Atomic Structure:
    • Protons (p^+): Positively charged particles, located in the nucleus. Determine the atomic number (Z) and identity of the element.
    • Neutrons (n^0): Neutrally charged particles, located in the nucleus. Contributes to the mass number and forms isotopes.
    • Electrons (e^-): Negatively charged particles, orbit the nucleus in electron shells or energy levels. Determine chemical reactivity and bonding.
  • Atomic Number (Z): Number of protons in an atom's nucleus.
  • Mass Number (A): Total number of protons and neutrons in an atom's nucleus.
  • Isotopes: Atoms of the same element (same Z) but with different numbers of neutrons (different A).

3. States of Matter

  • Solid: Definite shape and volume; particles are tightly packed and vibrate in fixed positions.
  • Liquid: Definite volume but no definite shape; particles are close together but can move past each other.
  • Gas: No definite shape or volume; particles are far apart and move randomly and rapidly.
  • Plasma: Ionized gas; extremely high energy state where electrons are stripped from atoms (e.g., in stars, lightning).
  • Phase Transitions: Changes between states of matter (e.g., melting, freezing, boiling, condensation, sublimation, deposition).

4. Chemical Bonding and Reactions

4.1 Chemical Bonds
  • Ionic Bond: Formed between a metal and a non-metal, involving the transfer of electrons, creating ions (cations and anions) that attract each other (e.g., NaCl).
  • Covalent Bond: Formed between two non-metals, involving the sharing of electrons (e.g., H_2O).
    • Polar Covalent: Unequal sharing of electrons due to differences in electronegativity.
    • Nonpolar Covalent: Equal sharing of electrons.
  • Metallic Bond: Occurs between metal atoms, where electrons are delocalized and shared among a lattice of positive metal ions (electron sea model).
4.2 Chemical Reactions
  • A process that involves the rearrangement of the atomic structure of substances, leading to the formation of new substances.
  • Reactants: Starting substances in a chemical reaction.
  • Products: Substances formed from a chemical reaction.
  • Law of Conservation of Mass: Mass is neither created nor destroyed during a chemical reaction; the total mass of reactants equals the total mass of products.
  • Chemical Equations: Symbolic representations of chemical reactions, showing reactants, products, and their relative quantities.
    • Example: 2H2(g) + O2(g) \rightarrow 2H_2O(l)
  • Types of Reactions:
    • Combination/Synthesis: A + B \rightarrow AB
    • Decomposition: AB \rightarrow A + B
    • Single Displacement: A + BC \rightarrow AC + B
    • Double Displacement: AB + CD \rightarrow AD + CB
    • Combustion: Substance reacts with oxygen, often producing heat and light (e.g., CH4 + 2O2 \rightarrow CO2 + 2H2O).
    • Acid-Base (Neutralization): Acid reacts with a base to form salt and water.

5. Stoichiometry

  • The quantitative study of reactants and products in chemical reactions.
  • Mole (mol): A unit of amount of substance; 1 mole contains 6.022 \times 10^{23} particles (Avogadro's number).
  • Molar Mass: The mass of one mole of a substance (g/mol).

6. Acids and Bases

  • Acids: Substances that produce hydrogen ions (H^+) in solution (Arrhenius definition) or donate protons (Brønsted-Lowry definition).
  • Bases: Substances that produce hydroxide ions (OH^-) in solution (Arrhenius definition) or accept protons (Brønsted-Lowry definition).
  • pH Scale: Measures the acidity or basicity of a solution (0-14);