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

• Atoms are stable when their outermost energy level is full.

Elements and the Periodic Table

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

• There are about 90 naturally occurring elements; only 25 are essential for life.

• Atomic number: Number of protons in an atom (also equals number of electrons in a neutral atom).

• Atomic mass: Sum of protons and neutrons.

Isotopes and Ions

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

• Ions: Atoms with a net charge due to loss or gain of electrons.

  • Cation: Positively charged (lost electrons).

  • Anion: Negatively charged (gained electrons).

Chemical Bonds

• Covalent Bonds: Atoms share electrons.

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

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

• Ionic Bonds: Formed when electrons are transferred from one atom to another, resulting in oppositely charged ions that attract (e.g., Na^+ + Cl^- 12 NaCl).

• Hydrogen Bonds: Weak attractions between a hydrogen atom (in a polar molecule) and another electronegative atom; important in water and biological molecules.

Properties of Water

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

• Cohesion: Water molecules stick to each other.

• Adhesion: Water molecules stick to other substances (causes meniscus and capillary action).

• High specific heat capacity: Water absorbs a lot of heat before changing temperature.

• Versatile solvent: Dissolves many substances due to polarity.

• Evaporative cooling: Removes heat as water evaporates (e.g., sweating).

Solutions and pH

• Solution: Homogeneous mixture of solute (substance dissolved) and solvent (substance doing the dissolving; water is the universal solvent).

• pH measures the concentration of hydrogen ions (H+) versus hydroxide ions (OH-).

• pH scale: 0 (acidic) to 14 (basic); 7 is neutral.

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

Chemical Equations

• Represent chemical reactions: Reactants 12 Products.

• Chemical equation example: 6O2 + C6H12O6 12 6CO2 + 6H2O + A0energy

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