Study Guide: Chapter 2 - The Nature of Molecules and the Properties of Water

Matter: Defined as anything that has mass and occupies space.
Atoms: The smallest unit of matter composed of three primary particles:
- Protons: Positively charged particles located in the nucleus.
- Neutrons: Neutral particles also found in the nucleus.
- Electrons: Negatively charged particles that orbit around the nucleus.
Atomic Number: The number of protons in an atom, which uniquely identifies an element.
Atomic Mass: The total mass of an atom, calculated by adding the number of protons and neutrons.

Ions: Atoms that have gained or lost electrons, resulting in a charge:
- Cations: Positively charged ions (loss of electrons).
- Anions: Negatively charged ions (gain of electrons).
Isotopes: Variants of the same element that differ in the number of neutrons:
- Radioactive Isotopes: These isotopes decay over time and emit radiation. Their decay rate can be measured using a concept called half-life.

Electron Configuration: Refers to the arrangement of electrons in an atom's orbitals:
- Valence Electrons: The electrons in the outermost shell of an atom that participate in chemical bonding.
Octet Rule: Atoms tend to gain, lose, or share electrons to achieve a full outer shell of 8 electrons, leading to stability.
Redox Reactions: Chemical reactions that involve the transfer of electrons:
- Oxidation: The process of losing electrons.
- Reduction: The process of gaining electrons.

Ionic Bonds: Formed between oppositely charged ions (e.g., sodium ion Na+ and chloride ion Cl-).
Covalent Bonds: Formed when two atoms share electrons:
- Polar Covalent Bonds: Electrons are shared unequally between atoms, leading to partial charges.
- Nonpolar Covalent Bonds: Electrons are shared equally between atoms.
Hydrogen Bonds: Weak attractions between polar molecules, significant in water's properties.
Van der Waals Forces: Weak, non-directional attractions that occur between adjacent atoms.

Chemical Reactions: Processes where reactants transform into products, involving the formation and breaking of bonds:
- Reactants → Products
Factors affecting reactions include:
- Temperature: Higher temperatures generally increase reaction rates.
- Concentration: Higher concentrations of reactants can increase reaction frequency.
- Catalysts: Substances that speed up reactions without being consumed themselves.
Many chemical reactions are reversible.

Unique Properties of Water: Result from hydrogen bonding:
- Cohesion: Water molecules stick to one another, which contributes to surface tension.
- Adhesion: Water molecules stick to other polar substances, aiding processes such as capillary action.
- High Specific Heat: Water requires a lot of energy to change temperature, helping stabilize environmental temperatures.
- High Heat of Vaporization: Water absorbs significant amounts of energy as it evaporates, cooling the environment.
- Less Density of Ice: Ice is less dense than liquid water, allowing it to float on water.

Solvent Properties of Water: Water is an excellent solvent for various substances:
- Hydrophilic Substances: Polar and ionic substances that dissolve readily in water.
- Hydrophobic Substances: Nonpolar substances that do not dissolve in water and tend to group together.

pH Scale: Measures the concentration of hydrogen ions in a solution:
- Low pH: Indicates an acidic solution.
- High pH: Indicates a basic (alkaline) solution.
Acids and Bases:
- Acids: Substances that donate H+ ions when dissolved in water.
- Bases: Substances that accept H+ ions in solution.
Buffers: Chemical systems that stabilize pH by donating or absorbing H+ ions, often composed of acid-base pairs, they play a crucial role in maintaining homeostasis in biological systems.