Atoms and Subatomic Particles

• An atom is the smallest unit of an element, consisting of a nucleus (containing protons and neutrons) and electrons orbiting in energy levels.

• Protons: Positively charged particles in the nucleus.

• Neutrons: Neutral particles in the nucleus.

• Electrons: Negatively charged particles found in energy levels around the nucleus.

Energy Levels and Electron Configuration

• Electrons occupy specific energy levels; each level holds a maximum number of electrons (first: 2, second: 8, third: 18).

• Electron configuration determines the stability of an atom; a full outer energy level is associated with stability.

Elements and the Periodic Table

• An element is a substance that cannot be broken down into simpler substances; each has a unique atomic number (number of protons).

• Atomic mass is the sum of protons and neutrons.

• Isotopes are atoms of the same element with different numbers of neutrons.

Ions

• Ions are charged atoms formed by gaining or losing electrons; cations are positive (loss of electrons), anions are negative (gain of electrons).

• The number of protons does not change when forming ions.

Chemical Bonds

• Covalent bonds: Atoms share electrons (can be polar or nonpolar).

• Polar covalent bonds: Electrons are shared unequally, leading to partial charges (e.g., H2O).

• Nonpolar covalent bonds: Electrons are shared equally (e.g., H2).

• Ionic bonds: Formed when atoms transfer electrons, resulting in oppositely charged ions that attract (e.g., NaCl).

• Hydrogen bonds: Weak attractions between a hydrogen atom in one molecule and an electronegative atom in another, important in water and biological molecules.

Properties of Water

• Water is a polar molecule, leading to hydrogen bonding.

• Exhibits cohesion (attraction between water molecules) and adhesion (attraction to other substances), causing phenomena like meniscus and capillary action.

• High specific heat capacity allows water to absorb heat without large temperature changes.

• Acts as a versatile solvent due to polarity.

Solutions and pH

• A solution consists of a solute (substance dissolved) and a solvent (substance doing the dissolving; water is a common solvent).

• pH measures the concentration of hydrogen ions (H+) and hydroxide ions (OH-) in a solution; scale ranges from 0 (acidic) to 14 (basic), with 7 being neutral.

• Acids increase H+ concentration; bases increase OH- concentration.

Chemical Equations

• Represent chemical reactions, showing reactants and products.

• Coefficients indicate the number of molecules; subscripts indicate the number of atoms in a molecule.

• Example: 6CO2 + 6H2O ightarrow C6H12O6 + 6O2 (photosynthesis).