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.

• Proton: Positively charged particle in the nucleus.

• Neutron: Neutral particle in the nucleus.

• Electron: Negatively charged particle outside the nucleus.

Energy Levels and Electron Configuration

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

• Each energy level has a maximum electron capacity:

  • First level: 2 electrons

  • Second level: 8 electrons

  • Third level: 18 electrons

• Stability is achieved when energy levels are filled according to these capacities.

Elements and the Periodic Table

• An element is a 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: Atomic bsp;Mass = Number bsp;of bsp;Protons + Number bsp;of bsp;Neutrons

Ions and Isotopes

• Ions are atoms with a net charge due to loss or gain of electrons.

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

Chemical Bonds

• Covalent Bonds: Atoms share electrons (e.g., H2, O2).

• Polar Covalent Bonds: Electrons are shared unequally, creating partial charges (e.g., H2O).

• Ionic Bonds: Formed by transfer of electrons between atoms, resulting in oppositely charged ions (e.g., Na^+ + Cl^- → NaCl).

• Hydrogen Bonds: Weak attractions between polar molecules, important in water and biological molecules.

Properties of Water

• Water is polar, allowing it to form hydrogen bonds.

• Exhibits cohesion (attraction between water molecules) and adhesion (attraction to other substances).

• High specific heat capacity and excellent solvent properties.

Solutions and pH

• Solutions consist of a solute (substance dissolved) and a solvent (substance doing the dissolving, often water).

• pH measures hydrogen ion (H+) concentration:

  • pH < 7: Acidic

  • pH = 7: Neutral

  • pH > 7: Basic

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 → C6H12O6 + 6O2