Chemistry, the central science, provides the foundation for understanding the material world around us.1 It is the study of matter—its properties, how and why it undergoes change, and the energy associated with these processes.2 A comprehensive set of chemistry notes must begin with the basics, defining what matter is and introducing the fundamental building blocks: atoms and molecules. Understanding these concepts is paramount to progressing through the subject. View More click here.

Atomic Structure and the Periodic TableThe atom, derived from the Greek word atomos (indivisible), is the smallest unit of an element that retains the chemical properties of that element.3 Modern chemistry notes describe the atom as consisting of a dense, positively charged nucleus containing protons and neutrons, surrounded by negatively charged electrons occupying specific energy levels or shells.4 The number of protons defines the atomic number (5$Z$) and determines the element’s identity, a key piece of information for any student compiling their chemistry notes.6ShutterstockExploreThe organization of elements is captured in the Periodic Table, arguably the most important tool in all of chemistry.7 Dmitri Mendeleev first developed it, arranging elements by increasing atomic mass and observing periodic trends in their properties.8 Today, elements are arranged by increasing atomic number.

Elements in the same vertical column (a group) share similar chemical properties because they have the same number of valence electrons (outer shell electrons).9 Elements in the same horizontal row (a period) show gradual changes in properties, and recognizing these trends is a critical skill acquired through meticulous study and detailed chemistry notes.10Chemical Bonding and Molecular GeometryThe forces that hold atoms together in compounds are known as chemical bonds.11 Atoms bond primarily to achieve a more stable, lower-energy electron configuration, often resembling that of a noble gas. There are two major types of bonds that must be included in any thorough set of chemistry notes: ionic bonds, which form from the electrostatic attraction between oppositely charged ions created by the transfer of electrons (typically between a metal and a nonmetal), and covalent bonds, which form when atoms share electrons (typically between two nonmetals).

The way atoms are connected and arranged in space is called molecular geometry, which dictates a molecule’s physical and chemical properties, including its polarity.12 The Valence Shell Electron Pair Repulsion (VSEPR) theory is a simple yet powerful model used to predict the geometry of molecules based on the repulsion between electron pairs in the valence shell of the central atom.13 Accurate depiction of these geometries, such as linear, trigonal planar, and tetrahedral, is often achieved through diagrams and detailed explanations within effective chemistry notes.Chemical Reactions and StoichiometryA chemical reaction is a process that leads to the transformation of one set of chemical substances (reactants) to another (products).14 These transformations involve the breaking of existing bonds and the formation of new ones. A balanced chemical equation provides a symbolic representation of a chemical reaction, showing the relative amounts of reactants and products involved.15 A foundational law in this area, essential for any good chemistry notes, is the Law of Conservation of Mass, which states that mass is neither created nor destroyed in a chemical reaction.16Stoichiometry is the area of chemistry that deals with the quantitative relationships between reactants and products in chemical reactions.17 It allows chemists to predict the amount of product that can be formed from a specific amount of reactant, or vice-versa.

The central concept in stoichiometry is the mole (18$N_A \approx 6.022 \times 10^{23}$ particles), which provides a bridge between the macroscopic masses we measure in a lab and the microscopic world of atoms and molecules.19 Mastering mole calculations is a non-negotiable step in creating comprehensive chemistry notes.States of Matter and ThermochemistryMatter exists generally in three macroscopic states: solid, liquid, and gas.20 The state of matter is primarily determined by the balance between the kinetic energy of the particles and the strength of the intermolecular forces (IMFs) between them. Solids have strong IMFs, leading to fixed shape and volume; gases have very weak IMFs, resulting in no fixed shape or volume; and liquids are an intermediate case.21 Discussions of IMFs—including London dispersion forces, dipole-dipole interactions, and hydrogen bonding—are vital inclusions in any study of the states of matter within one’s chemistry notes.22