Chemistry: Matter, Properties, Atoms, Molecules, Ions

• Chemistry is the study of matter and its properties as well as how matter changes
• Physical chemistry is the study of the fundamental physical principles that govern the properties and behavior of chemical systems

Matter and its Properties

• Matter is anything that has mass and takes up space
• Matter can exist in three states: solid, liquid, and gas; plasma is sometimes considered a fourth state
• Properties of matter can be physical or chemical
• Physical properties are those that can be observed or measured without changing the composition of the substance, such as color, density, and boiling point
• Chemical properties describe how a substance changes into a new substance, such as flammability or reactivity with acid

Atoms, Molecules, and Ions

• Atoms are the smallest unit of an element that retains the chemical properties of that element
• Molecules are two or more atoms held together by chemical bonds
• Ions are atoms or molecules that have gained or lost electrons, resulting in an electrical charge
• Cations are positively charged ions and anions are negatively charged ions

Chemical Bonds

• Chemical bonds are the attractive forces that hold atoms together in molecules and compounds
• Ionic bonds result from the transfer of electrons between atoms, typically between a metal and a nonmetal
• Covalent bonds result from the sharing of electrons between atoms, typically between two nonmetals
• Metallic bonds are found in metals, where electrons are delocalized and shared among many atoms

Chemical Reactions

• Chemical reactions involve the rearrangement of atoms and molecules to form new substances
• Chemical equations represent chemical reactions using chemical formulas and symbols
• Balancing chemical equations ensures that the number of atoms of each element is the same on both sides of the equation
• Stoichiometry deals with the quantitative relationships between reactants and products in chemical reactions
• Factors affecting reaction rates include concentration, temperature, catalysts, and surface area

States of Matter

• Solids have a fixed shape and volume due to strong intermolecular forces
• Liquids have a fixed volume but take the shape of their container due to weaker intermolecular forces
• Gases have no fixed shape or volume and are highly compressible due to very weak intermolecular forces
• Phase transitions are the processes by which matter changes from one state to another, such as melting, boiling, and sublimation

Thermodynamics

• Thermodynamics is the study of energy and its transformations
• The first law of thermodynamics states that energy is conserved
• The second law of thermodynamics states that the entropy of an isolated system always increases
• Enthalpy is a measure of the heat content of a system
• Entropy is a measure of the disorder or randomness of a system
• Gibbs free energy is a measure of the spontaneity of a process

Chemical Kinetics

• Chemical kinetics is the study of reaction rates and mechanisms
• Reaction rate is the change in concentration of reactants or products per unit time
• Rate laws express the relationship between reaction rate and the concentrations of reactants
• Reaction mechanisms describe the step-by-step sequence of elementary reactions that make up an overall reaction; the slowest step is the rate-determining step
• Catalysts speed up reactions by providing an alternative reaction pathway with a lower activation energy

Chemical Equilibrium

• Chemical equilibrium is the state in which the rates of the forward and reverse reactions are equal, and the net change in concentrations of reactants and products is zero
• The equilibrium constant K is a measure of the relative amounts of reactants and products at equilibrium
• Le Chatelier's principle states that if a change of condition is applied to a system in equilibrium, the system will shift in a direction that relieves the stress
• Factors that can affect chemical equilibrium include concentration, temperature, and pressure

Solutions

• A solution is a homogeneous mixture of two or more substances
• The solute is the substance being dissolved, and the solvent is the substance doing the dissolving
• Concentration is the amount of solute present in a given amount of solvent or solution
• Molarity is the number of moles of solute per liter of solution
• Solubility is the maximum amount of solute that can dissolve in a given amount of solvent at a specific temperature

Acids and Bases

• Acids are substances that donate protons (H+) and bases are substances that accept protons
• pH is a measure of the acidity or basicity of a solution
• Acid-base reactions involve the transfer of protons from an acid to a base
• Buffers are solutions that resist changes in pH when small amounts of acid or base are added

Electrochemistry

• Electrochemistry is the study of the relationship between electricity and chemical reactions
• Oxidation is the loss of electrons, and reduction is the gain of electrons
• Electrochemical cells convert chemical energy into electrical energy (galvanic cells) or electrical energy into chemical energy (electrolytic cells)
• Electrolysis is the process of using electrical energy to drive a non-spontaneous chemical reaction

Quantum Mechanics and Atomic Structure

• Quantum mechanics describes the behavior of matter at the atomic and subatomic level
• Electrons in atoms exist in specific energy levels or orbitals
• Atomic orbitals are described by quantum numbers: principal (n), angular momentum (l), magnetic (ml), and spin (ms)
• Electron configuration describes the arrangement of electrons within an atom

Chemical Bonding and Molecular Structure

• Valence bond theory describes covalent bonds as the overlap of atomic orbitals
• Hybridization is the mixing of atomic orbitals to form new hybrid orbitals with different shapes and energies
• Molecular orbital theory describes covalent bonds as the combination of atomic orbitals to form molecular orbitals, which are delocalized over the entire molecule
• Sigma (σ) bonds are formed by end-to-end overlap of orbitals, and pi (π) bonds are formed by side-to-side overlap of orbitals

Spectroscopy

• Spectroscopy is the study of the interaction of electromagnetic radiation with matter
• Different types of spectroscopy include UV-Vis, IR, NMR, and mass spectrometry
• Spectroscopy can be used to identify and quantify substances, as well as to study their structure and properties

Statistical Mechanics

• Statistical mechanics provides a connection between microscopic properties of individual molecules and macroscopic properties of bulk materials
• It uses probability theory to predict the average behavior of a large number of particles
• Key concepts include ensembles, partition functions, and Boltzmann distribution

Properties of Liquids and Solids

• Intermolecular forces (van der Waals forces, hydrogen bonding) determine many physical properties of liquids and solids
• Surface tension, viscosity, and vapor pressure are important properties of liquids
• Crystalline solids have a long-range order, while amorphous solids lack long-range order
• Crystal structures can be described by unit cells and lattice parameters

Polymers

• Polymers are large molecules made up of repeating structural units called monomers
• Polymer properties depend on the chemical structure of the monomer, the chain length, and the intermolecular forces between chains
• Polymerization reactions can be addition or condensation reactions
• Examples of polymers include polyethylene, polystyrene, and nylon

Solutions and Colligative Properties

• Colligative properties depend on the concentration of solute particles, but not on their identity
• Examples of colligative properties include boiling point elevation, freezing point depression, and osmotic pressure
• Raoult's law describes the vapor pressure of a solution as a function of the mole fraction of the solvent

Surface Chemistry and Colloids

• Surface chemistry deals with phenomena occurring at interfaces
• Adsorption is the process of a substance adhering to a surface
• Colloids are mixtures with particles larger than molecules but small enough to remain dispersed
• Examples of colloids include milk, paint, and aerosols