Atoms and Subatomic Particles

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

• Protons are positively charged particles found in the nucleus.

• Neutrons are neutral particles also located in the nucleus.

• Electrons are negatively charged particles that move around the nucleus in energy levels.

Energy Levels and Electron Configuration

• Electrons occupy specific energy levels (shells) around the nucleus.

• Each energy level can hold a maximum number of electrons:

  • First level: 2 electrons

  • Second level: 8 electrons

  • Third level: 18 electrons

• Stability is achieved when all occupied energy levels are filled according to their capacity.

Elements and the Periodic Table

• An element is a pure substance that cannot be broken down into simpler substances.

• Each element is defined by its atomic number (number of protons).

• Atomic mass is the sum of protons and neutrons in the nucleus.

Determining Subatomic Particles

• Number of protons = atomic number.

• Number of electrons = atomic number (for neutral atoms).

• Number of neutrons = atomic mass - atomic number.

Ions and Isotopes

• Ions are atoms with a net charge due to loss or gain of electrons (cation: positive, anion: negative).

• Isotopes are atoms of the same element with different numbers of neutrons (e.g., Carbon-12, Carbon-13, Carbon-14).

Chemical Bonds

• Covalent Bonds: Atoms share electrons; can be polar (unequal sharing, e.g., H2O) or nonpolar (equal sharing, e.g., H2).

• Ionic Bonds: Formed when atoms transfer electrons, resulting in oppositely charged ions that attract (e.g., Na+ + Cl- → 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).

• High specific heat capacity allows water to absorb significant heat before changing temperature.

• Excellent solvent due to polarity, dissolving many substances.

Solutions, Acids, and Bases

• 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+) versus hydroxide ions (OH-); scale ranges from 0 (acidic) to 14 (basic), with 7 being neutral.

Chemical Equations

• Represent chemical reactions, showing reactants and products.

• Chemical equations must be balanced; coefficients indicate the number of molecules or atoms involved.

• Subscripts in chemical formulas indicate the number of atoms of each element in a molecule.

• Example equation (photosynthesis): 6CO2+6H2O→C6H12O6+6O2