Chemistry Fundamentals

This deck is designed to give you a solid grounding in the most essential ideas in chemistry. You'll start with the basics of matter and its three common states, then move into the building blocks of everything around us: atoms, subatomic particles, and the concepts of atomic and mass numbers. From there, you'll explore how elements are organized in the periodic table, learn to tell the difference between metals, nonmetals, and metalloids, and get clear definitions for key terms like compounds, mixtures, and isotopes.

It's a great fit if you're just beginning a chemistry course, preparing for an introductory exam, or simply curious about the science behind everyday materials. Even if you've studied some chemistry before, working through these cards can be a quick way to refresh terms you may not have used in a while and make sure your foundations are strong before tackling more advanced topics like reactions or bonding.

To get the most out of your study sessions, try working through the deck in small chunks rather than all at once, and come back to it over several days so your memory has time to settle. Before you flip a card, pause and try to answer in your own words first, then check how closely it matches the back. Connecting new ideas to everyday examples, like thinking about water as a familiar compound, can also help the definitions stick far beyond a single review.

Chemistry is the scientific study of matter, its properties, composition, structure, and the changes it undergoes during chemical reactions. At its most basic level, matter is anything that has mass and occupies space. It exists in three primary states: solid, liquid, and gas. Solids have a definite shape and volume, liquids have a definite volume but take the shape of their container, and gases have neither a definite shape nor volume, expanding to fill whatever space is available.

All matter can be classified into pure substances and mixtures. A pure substance is either an element or a compound. An element is a substance that cannot be broken down into simpler substances by chemical means and is made of only one type of atom. A compound, in contrast, is composed of two or more different elements chemically bonded together in fixed proportions. A mixture, on the other hand, is a combination of two or more substances that are not chemically combined, allowing each to retain its individual properties. Mixtures may be homogeneous, having a uniform composition throughout, or heterogeneous, where the components remain visibly distinct.

The atom is the smallest unit of an element that retains the chemical properties of that element. Every atom consists of a nucleus surrounded by electrons. The nucleus contains two main subatomic particles: protons, which carry a positive charge, and neutrons, which carry no charge. Electrons, which carry a negative charge, orbit the nucleus. The atomic number of an element equals the number of protons in its nucleus and uniquely identifies the element, while the mass number is the total count of protons and neutrons. Because isotopes are atoms of the same element with the same number of protons but different numbers of neutrons, they share an atomic number but have different mass numbers.

The periodic table is a tabular arrangement of all known chemical elements, organized by increasing atomic number. It reveals periodic trends in chemical properties that recur across the table. Dmitri Mendeleev is credited with creating the modern version of this table in 1869. He arranged the elements by atomic mass and, remarkably, left gaps for elements that had not yet been discovered, predicting their properties with striking accuracy.

The table is divided into horizontal rows called periods and vertical columns called groups, or families. Periods indicate the energy levels of an atom's electrons, while groups contain elements with similar chemical behavior because they share the same number of valence electrons. Elements within the same group tend to react in comparable ways and form similar compounds.

Across the periodic table, elements are classified into three broad categories based on their properties. Metals, found on the left side and in the center of the table, are typically shiny, malleable, and good conductors of heat and electricity. Nonmetals, located on the right side, tend to be dull, brittle, and poor conductors. Along a staircase-shaped boundary between these two regions sit the metalloids, which exhibit properties intermediate between metals and nonmetals, making them valuable as semiconductors in electronic devices.

Atoms combine with one another through chemical bonds to form more stable arrangements. The two principal types of bonding are ionic and covalent. Ionic bonding occurs when a metal transfers one or more electrons to a nonmetal, creating positively and negatively charged ions, called cations and anions, which are then held together by electrostatic attraction. Covalent bonding, by contrast, involves the sharing of electrons between nonmetal atoms, allowing each atom to achieve a more stable electron configuration.

When two or more atoms join together through covalent bonds, they form a molecule, which represents the smallest unit of a covalent compound. The behavior of atoms in bonding is largely determined by their valence electrons, the electrons in the outermost electron shell. These are the electrons involved in forming chemical bonds, and the number of valence electrons an atom possesses dictates how it interacts with other atoms.

Chemists represent valence electrons visually using Lewis dot structures, which place dots around an atomic symbol to show both bonding and nonbonding, or lone pair, electrons. These diagrams make it possible to predict how atoms will connect, how many bonds a particular atom can form, and what the resulting molecule might look like. Together, ionic and covalent bonding explain the vast diversity of substances found in the natural world.

A chemical reaction is a process in which reactants, the starting substances, are transformed into products through the breaking and forming of chemical bonds. The substances that enter the reaction are reorganized at the atomic level to produce new substances with different properties. A balanced chemical equation represents this transformation by using coefficients to ensure that the same number of each type of atom appears on both sides of the equation. This balance is required by the law of conservation of mass, which states that mass is neither created nor destroyed during a chemical reaction, so the total mass of reactants must equal the total mass of products.

Chemists classify reactions into five main types. In a synthesis reaction, two or more substances combine to form a single product. A decomposition reaction reverses this, breaking a single compound into simpler substances. In a single replacement reaction, one element replaces another in a compound, while a double replacement reaction involves an exchange of ions between two compounds. Combustion reactions occur when a fuel reacts with oxygen, typically producing carbon dioxide and water, as in the burning of hydrocarbons.

Quantitative chemistry depends on the concept of the mole, the SI unit for amount of substance. One mole contains Avogadro's number of particles, which is \(6.022 \times 10^{23}\). The molar mass of a substance, expressed in grams per mole, is calculated by summing the atomic masses of all atoms in its chemical formula. Stoichiometry uses these relationships and balanced equations to calculate the amounts of reactants and products involved in a chemical change. In any reaction, the limiting reactant is the substance consumed first, and it determines the maximum amount of product that can be formed.

The behavior of gases, liquids, and solids is explained by the kinetic molecular theory, which describes matter in terms of moving particles. According to this theory, the particles of a gas are in constant, random motion, have negligible volume compared to the space between them, and undergo elastic collisions in which no kinetic energy is lost. The average kinetic energy of these particles is directly proportional to the absolute temperature of the gas.

Phase changes occur at specific temperatures. The melting point is the temperature at which a solid becomes a liquid at standard pressure, while the boiling point is the temperature at which a liquid's vapor pressure equals the surrounding atmospheric pressure, allowing it to transition into a gas. Vapor pressure is the pressure exerted by the vapor of a liquid in equilibrium with its liquid phase at a given temperature. These transitions are strongly influenced by intermolecular forces, the attractions that exist between molecules. The three main types are hydrogen bonding, dipole-dipole interactions, and London dispersion forces. Substances with stronger intermolecular forces generally have higher melting and boiling points.

A solution is a homogeneous mixture formed when one substance dissolves in another. The solute is the substance being dissolved, usually present in a smaller amount, while the solvent is the dissolving medium, typically present in greater quantity. Concentration is commonly expressed as molarity, defined as the number of moles of solute per liter of solution, written as \(M = \text{mol/L}\). Solubility depends on several factors, including temperature, which generally increases the solubility of solids but decreases that of gases; pressure, which affects gas solubility according to Henry's law, meaning the solubility of a gas in a liquid is directly proportional to its partial pressure above the liquid; and the chemical nature of the solute and solvent, summarized by the principle that "like dissolves like."

According to the Arrhenius definition, an acid is a substance that increases the concentration of hydrogen ions, often written as \(H^+\) or \(H_3O^+\), when dissolved in water, as in the dissociation of hydrochloric acid. An Arrhenius base, by contrast, increases the concentration of hydroxide ions, \(OH^-\), in water, as sodium hydroxide does when it dissociates in solution. The pH scale quantifies the acidity or basicity of a solution on a range from 0 to 14, with values below 7 indicating acidic solutions, a value of 7 indicating neutrality, and values above 7 indicating basic, or alkaline, solutions. Mathematically, pH is defined as the negative logarithm of the hydrogen ion concentration, written as \(pH = -\log[H^+]\).

When an acid and a base react, they undergo a neutralization reaction to produce a salt and water, such as in the classic reaction of hydrochloric acid with sodium hydroxide. Buffer solutions resist changes in pH when small amounts of acid or base are added, and they typically consist of a weak acid together with its conjugate base. This buffering capacity is essential in biological systems and in many industrial processes where stable pH conditions are required.

Every chemical reaction also involves energy changes, which are described by the concept of enthalpy, or the total heat content of a system at constant pressure. The change in enthalpy, denoted \(\Delta H\), indicates whether a reaction releases or absorbs heat. Exothermic reactions release heat to the surroundings and have a negative \(\Delta H\), with combustion being a familiar example. Endothermic reactions absorb heat from the surroundings and have a positive \(\Delta H\), as in photosynthesis. For a reaction to proceed, the reactants must overcome an energy barrier called the activation energy, often visualized as the peak in an energy diagram. Several factors influence how fast a reaction proceeds, including the concentration of reactants, temperature, surface area of solids, the presence of catalysts, and the inherent chemical nature of the reacting substances.