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 $(H<em>2O)$, Carbon Dioxide $(CO</em>2)$). 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: $2H<em>2(g) + O</em>2(g) \rightarrow 2H_2O(l)$
• 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., $CH<em>4 + 2O</em>2 \rightarrow CO<em>2 + 2H</em>2O$).
  • 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 ($0-14$); $<7$ is acidic, $>7$ is basic, $7$ is neutral.