Introduction to Chemistry

Chemistry is the study of matter and its properties as well as how matter changes
Matter is anything that has mass and takes up space (volume)
A chemical is a substance with a defined composition

Physical properties: Characteristics that can be observed or measured without changing the substance's composition (e.g., color, density, melting point)
Chemical properties: Describe how a substance changes into a new substance (e.g., flammability, reactivity)

Physical change: Alters the form or appearance of a substance but does not change its chemical composition (e.g., melting ice)
Chemical change: Involves the rearrangement of atoms to form new substances (e.g., burning wood)
Indicators of a chemical change include color change, gas production, precipitate formation, and heat absorption or release

Mixture: A combination of two or more substances that are physically combined
Homogeneous mixture: Has uniform composition throughout (e.g., saltwater)
Heterogeneous mixture: Does not have uniform composition throughout (e.g., sand and water)
Solutions are homogeneous mixtures
Methods for separating mixtures: Filtration, distillation, evaporation, chromatography

Element: A pure substance that cannot be broken down into simpler substances by chemical means (e.g., gold, oxygen)
Compound: A pure substance composed of two or more elements chemically combined in a fixed ratio (e.g., water, salt)
Law of definite proportions: A given chemical compound always contains its component elements in fixed ratio (by mass) and does not depend on its origin and method of preparation
Molecule: Two or more atoms held together by chemical bonds

Atom: The smallest unit of an element that retains the chemical properties of that element
Atomic structure: Consists of protons, neutrons, and electrons
Protons: Positively charged particles located in the nucleus
Neutrons: Neutral particles located in the nucleus
Electrons: Negatively charged particles orbiting the nucleus
Atomic number: Number of protons in an atom
Mass number: Number of protons and neutrons in an atom
Isotopes: Atoms of the same element with different numbers of neutrons

Ionic bond: Formed through the transfer of electrons between atoms, creating ions
Cation: Positively charged ion
Anion: Negatively charged ion
Covalent bond: Formed through the sharing of electrons between atoms
Polar covalent bond: Unequal sharing of electrons
Nonpolar covalent bond: Equal sharing of electrons
Metallic Bond: Occurs between atoms of metallic elements

Chemical equation: Represents a chemical reaction using chemical formulas and symbols
Reactants: Substances that undergo change in a chemical reaction
Products: Substances that are formed in a chemical reaction
Balancing chemical equations: Ensuring the number of atoms of each element is the same on both sides of the equation, following the law of conservation of mass
Stoichiometry: The quantitative relationship between reactants and products in a chemical reaction
Mole: A unit of amount (6.022 x 10^23 particles)
Molar mass: The mass of one mole of a substance

Organic chemistry: The study of carbon-containing compounds
Carbon: Can form four covalent bonds, leading to a wide variety of structures
Functional groups: Specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules
Common functional groups: Hydroxyl (-OH), carbonyl (C=O), carboxyl (-COOH), amino (-NH2)
Hydrocarbons: Compounds containing only carbon and hydrogen
Alkanes, alkenes, and alkynes: Different types of hydrocarbons based on the types of bonds between carbon atoms (single, double, and triple, respectively)
Isomers: Molecules with the same molecular formula but different structural formulas

Thermodynamics is the study of energy and its transformations
System: The part of the universe being studied
Surroundings: Everything else in the universe outside of the system
Energy: The capacity to do work or transfer heat
Kinetic energy: Energy of motion
Potential energy: Stored energy
First law of thermodynamics: Energy cannot be created or destroyed, only converted from one form to another (conservation of energy)
Enthalpy (H): A thermodynamic property of a system that is the sum of the internal energy and the product of pressure and volume
Exothermic reaction: Releases heat (ΔH < 0)
Endothermic reaction: Absorbs heat (ΔH > 0)
Entropy (S): A measure of the disorder or randomness of a system
Second law of thermodynamics: The entropy of an isolated system tends to increase
Gibbs free energy (G): A thermodynamic potential that measures the amount of energy available in a system to do useful work at a constant temperature and pressure
ΔG = ΔH - TΔS, where T is the temperature in Kelvin
Spontaneous reaction: ΔG < 0

Kinetics is the study of reaction rates
Reaction rate: The speed at which reactants are converted into products
Factors affecting reaction rate: Concentration, temperature, surface area, and catalysts
Catalysts: Substances that speed up a reaction without being consumed in the reaction
Rate law: An equation that relates the rate of a reaction to the concentrations of the reactants
Activation energy: The minimum energy required for a reaction to occur

Chemical equilibrium: The state in which the rate of the forward reaction equals the rate of the reverse reaction
Equilibrium constant (K): A ratio of the concentrations of products to reactants at equilibrium
Le Chatelier's principle: If a change of condition is applied to a system in equilibrium, the system will shift in a direction that relieves the stress
Common stresses: Changes in concentration, pressure, temperature

Redox reactions: Reactions involving the transfer of electrons
Oxidation: Loss of electrons
Reduction: Gain of electrons
Oxidizing agent: A substance that causes oxidation by accepting electrons
Reducing agent: A substance that causes reduction by donating electrons
Oxidation number: A number assigned to an element in a chemical combination that represents the number of electrons lost or gained (if that number is positive or negative, respectively)

Solution: A homogeneous mixture of two or more substances
Solvent: The substance present in the largest amount
Solute: The substance(s) present in smaller amounts
Solubility: The maximum amount of solute that can dissolve in a given amount of solvent at a specific temperature
Factors affecting solubility: Temperature, pressure (for gases), and the nature of the solute and solvent
Concentration: The amount of solute in a given amount of solution
Molarity (M): Moles of solute per liter of solution
Molality (m): Moles of solute per kilogram of solvent
Colligative properties: Properties of solutions that depend on the concentration of solute particles, not on the identity of the solute
Examples of colligative properties: Vapor pressure lowering, boiling point elevation, freezing point depression, osmotic pressure