Introduction to Chemistry

• Chemistry is the study of matter, its properties, and how matter changes
• Matter is anything that has mass and occupies space
• Pure substances have constant composition and fixed properties
• Elements are substances that cannot be broken down by chemical means
• Compounds are substances with two or more elements chemically combined in a fixed ratio
• Mixtures combine two or more substances physically
• Homogeneous mixtures have uniform composition and properties throughout; these are also known as solutions
• Heterogeneous mixtures have non-uniform composition and properties
• Physical properties are observable/measurable without changing the substance's composition, like color, density, and melting point
• Chemical properties describe changes in composition through reactions, like flammability and reactivity with acid
• Physical changes do not alter a substance's composition, examples include melting and boiling
• Chemical changes involve altering the composition of a substance, such as burning or rusting
• Atoms are the smallest units of an element retaining its chemical properties
• Protons are positive particles in an atom's nucleus
• Neutrons are neutral particles in an atom's nucleus
• Electrons are negative particles orbiting the nucleus
• Atomic number (Z) is the number of protons in an atom's nucleus, defining the element
• Mass number (A) is the total number of protons and neutrons in an atom's nucleus
• Isotopes are atoms of the same element but with different numbers of neutrons
• Ions are atoms or molecules with a net electric charge due to gained or lost electrons
• Cations are positive ions formed by losing electrons
• Anions are negative ions formed by gaining electrons
• Molecules consist of two or more atoms held together by chemical bonds
• Chemical bonds are attractive forces holding atoms together in molecules or compounds
• Ionic bonds form through electrostatic attraction between oppositely charged ions
• Covalent bonds form through the sharing of electrons between atoms
• Metallic bonds form through electron sharing within a metal lattice
• Chemical reactions rearrange atoms and molecules
• Reactants are substances that undergo change in a chemical reaction
• Products are substances formed as a result of a chemical reaction
• Balanced chemical equations represent reaction stoichiometry, ensuring equal atom count of each element on both sides
• The mole (mol) is the SI unit for the amount of substance, equivalent to the number of entities in 12 grams of carbon-12
• Avogadro's number (NA) is about 6.022 x 10^23 entities in one mole
• Molar mass is the mass of one mole of a substance, expressed in grams per mole (g/mol)
• Stoichiometry is the quantitative relationship between reactants and products in a reaction
• A limiting reactant is fully consumed, determining maximum product formation
• Percent yield is the ratio of actual yield to theoretical yield, expressed as a percentage
• Solutions are homogeneous mixtures of multiple substances
• A solute is the substance being dissolved
• A solvent dissolves the solute
• Concentration is the amount of solute in a solvent or solution
• Molarity (M) is moles of solute per liter of solution (mol/L)
• Acids donate protons (H+) in aqueous solutions
• Bases accept protons (H+) in aqueous solutions
• pH measures acidity/basicity, defined as -log[H+]
• Acid-base reactions transfer protons from acids to bases
• Neutralization is the reaction between an acid and a base, producing salt and water
• Oxidation-reduction (redox) reactions transfer electrons
• Oxidation is the loss of electrons
• Reduction is the gain of electrons
• An oxidizing agent causes oxidation by accepting electrons
• A reducing agent causes reduction by donating electrons
• Thermodynamics studies energy changes in chemical and physical processes
• Energy enables work or heat transfer
• The first law of thermodynamics states energy is conserved
• Enthalpy (H) measures heat content at constant pressure
• Exothermic reactions release heat (ΔH < 0)
• Endothermic reactions absorb heat (ΔH > 0)
• Entropy (S) measures disorder or randomness
• The second law of thermodynamics states entropy increases in isolated systems over time
• Gibbs free energy (G) combines enthalpy and entropy to determine spontaneity
• Spontaneous processes occur without intervention (ΔG < 0)
• Chemical kinetics studies reaction rates and influencing factors
• Reaction rate is the change in reactant or product concentration per unit time
• Factors affecting reaction rate: temperature, concentration, surface area, catalysts
• A catalyst increases reaction rate without being consumed
• Equilibrium is when forward and reverse reaction rates are equal
• The equilibrium constant (K) is the ratio of product to reactant concentrations at equilibrium
• Le Chatelier's principle states that a system at equilibrium will shift to relieve stress from any applied change
• Organic chemistry studies carbon-containing compounds
• Carbon can form stable bonds with itself and other elements, leading to diverse organic molecules
• Hydrocarbons contain carbon and hydrogen
• Alkanes have only single bonds
• Alkenes have one or more double bonds
• Alkynes have one or more triple bonds
• Functional groups dictate characteristic chemical reactions of molecules
• Polymers are large molecules made of repeating monomers
• Polymerization joins monomers to form a polymer
• Biochemistry studies chemical processes in living organisms
• Carbohydrates, composed of C, H, and O, are primary energy sources
• Lipids, including fats, oils, and waxes, store energy and form cell membranes
• Proteins, polymers of amino acids, act as enzymes, structural components, and antibodies
• Nucleic acids (DNA and RNA) are polymers of nucleotides carrying genetic information
• Analytical chemistry separates, identifies, and quantifies chemical components
• Qualitative analysis determines presence/absence
• Quantitative analysis determines the amounts of specific substances
• Spectroscopy studies the interaction of electromagnetic radiation with matter
• Chromatography separates components based on differential distribution between phases

Nuclear Chemistry

• Nuclear chemistry involves reactions involving the nuclei of atoms
• Radioactivity is the spontaneous emission of particles or energy from unstable nuclei
• Alpha particles are helium nuclei (2 protons and 2 neutrons)
• Beta particles are high-speed electrons
• Gamma rays are high-energy photons
• Nuclear reactions involve changes in the composition of the nucleus
• Nuclear fission is the splitting of a heavy nucleus into lighter nuclei
• Nuclear fusion is the combining of light nuclei to form a heavier nucleus
• Half-life is the time it takes for half of the radioactive nuclei in a sample to decay