Introduction to Chemistry: Matter and Its Properties

• Chemistry is the study of matter and its properties as well as how matter changes

Matter

• Matter is anything that has mass and takes up space
• Matter exists in different states, including solid, liquid, gas, and plasma
• Solids have a definite shape and volume
• Liquids have a definite volume but take the shape of their container
• Gases have no definite shape or volume and can be compressed
• Plasma is a state of matter where a gas becomes ionized and carries an electrical charge

Properties of Matter

• Physical properties are those that can be observed or measured without changing the substance's composition, such as color, density, and boiling point
• Chemical properties describe how a substance reacts with other substances, such as flammability and reactivity with acids
• Intensive properties do not depend on the amount of substance present, such as temperature and density
• Extensive properties depend on the amount of substance present, such as mass and volume

Atoms

• An atom is the smallest unit of an element that retains the chemical properties of that element
• Atoms are composed of protons, neutrons, and electrons
• Protons are positively charged particles located in the nucleus
• Neutrons are neutral particles located in the nucleus
• Electrons are negatively charged particles that orbit the nucleus in electron shells or energy levels
• The number of protons in an atom defines the element and is called the atomic number
• Atoms of the same element with different numbers of neutrons are called isotopes
• The mass number is the sum of protons and neutrons in an atom

Molecules and Compounds

• A molecule is a group of two or more atoms held together by chemical bonds
• A compound is a substance consisting of two or more different elements chemically bonded together in a fixed ratio
• Chemical formulas represent the number and type of atoms in a molecule or compound
• Molecular formulas show the actual number of atoms of each element in a molecule
• Empirical formulas show the simplest whole-number ratio of atoms in a compound
• Structural formulas show the arrangement of atoms and bonds in a molecule

Chemical Bonds

• A chemical bond is an attraction between atoms that allows the formation of chemical substances
• Ionic bonds occur through the transfer of electrons between atoms, resulting in the formation of ions (charged particles)
• Covalent bonds occur through the sharing of electrons between atoms
• Metallic bonds occur in metals, where electrons are delocalized and shared among many atoms
• Hydrogen bonds are weak attractions between molecules containing hydrogen bonded to highly electronegative atoms (e.g., oxygen, nitrogen, fluorine)

Chemical Reactions

• A chemical reaction is a process that involves the rearrangement of atoms and molecules to form new substances
• Chemical equations represent chemical reactions, showing the reactants (starting materials) and products (resulting substances)
• Balancing chemical equations ensures that the number of atoms of each element is the same on both sides of the equation, following the law of conservation of mass
• Reaction types include synthesis, decomposition, single displacement, double displacement, and combustion

Stoichiometry

• Stoichiometry is the quantitative study of the relationships between reactants and products in chemical reactions
• The mole is the SI unit for the amount of substance, defined as the amount containing the same number of entities as there are atoms in 12 grams of carbon-12
• Molar mass is the mass of one mole of a substance, expressed in grams per mole (g/mol)
• Stoichiometric calculations involve using mole ratios from balanced chemical equations to determine the amounts of reactants and products

Acids and Bases

• Acids are substances that donate protons (H⁺) in aqueous solutions or accept electrons
• Bases are substances that accept protons or donate electrons
• The pH scale measures the acidity or basicity of a solution, with values ranging from 0 to 14
• Acidic solutions have a pH less than 7
• Basic or alkaline solutions have a pH greater than 7
• Neutral solutions have a pH of 7
• Strong acids and bases completely dissociate in water
• Weak acids and bases only partially dissociate in water
• Neutralization is the reaction between an acid and a base, resulting in the formation of a salt and water

Organic Chemistry

• Organic chemistry is the study of carbon-containing compounds
• Carbon atoms can form stable covalent bonds with other carbon atoms, allowing for the formation of long chains and complex structures
• Hydrocarbons are organic compounds containing only carbon and hydrogen
• Alkanes, alkenes, and alkynes are hydrocarbons with single, double, and triple bonds, respectively
• Functional groups are specific groups of atoms within molecules that are responsible for characteristic chemical reactions of those molecules
• Common functional groups include alcohols, ethers, aldehydes, ketones, carboxylic acids, and amines

Thermochemistry

• Thermochemistry is the study of heat and energy associated with chemical reactions and physical changes
• Energy is the capacity to do work or transfer heat
• Heat is the transfer of thermal energy between objects at different temperatures
• The first law of thermodynamics states that energy cannot be created or destroyed, only converted from one form to another
• Exothermic reactions release heat into the surroundings
• Endothermic reactions absorb heat from the surroundings
• Enthalpy (H) is a thermodynamic property that is used to describe the heat content of a system at constant pressure
• Hess's law states that the enthalpy change for a reaction is independent of the pathway taken

Chemical Kinetics

• Chemical kinetics is the study of reaction rates and the factors that affect them
• The reaction rate is the change in concentration of reactants or products per unit time
• Factors affecting reaction rates include temperature, concentration, surface area, and catalysts
• Catalysts are substances that speed up a reaction without being consumed in the process
• Reaction mechanisms describe the step-by-step sequence of elementary reactions that make up an overall reaction
• The rate-determining step is the slowest step in a reaction mechanism and determines the overall rate of the reaction

Chemical Equilibrium

• Chemical equilibrium occurs when the rate of the forward reaction equals the rate of the reverse reaction
• At equilibrium, the concentrations of reactants and products remain constant over time
• The equilibrium constant (K) is a quantitative measure of the extent to which a reaction proceeds to completion at a given temperature
• 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
• Changes in conditions include changes in concentration, pressure, and temperature