Introduction to Chemistry

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

Basic Concepts

• Matter is anything that has mass and takes up space.
• An element is a substance that cannot be broken down into simpler substances by chemical means; elements are the building blocks of all matter.
• A compound is a substance consisting of two or more different elements chemically bonded together in a fixed ratio.
• A mixture is a combination of two or more substances that are physically combined and can be separated by physical means.
• Homogeneous mixtures have uniform composition throughout such as saltwater.
• Heterogeneous mixtures do not have uniform composition such as salad.
• Atoms are the smallest unit of an element that retains the chemical properties of that element.
• Molecules are two or more atoms held together by chemical bonds.
• Ions are atoms or molecules that have gained or lost electrons, resulting in an electrical charge.
• Cations are positively charged ions formed by losing electrons.
• Anions are negatively charged ions formed by gaining electrons.

States of Matter

• Solids have a fixed shape and volume with particles tightly packed.
• Liquids have a fixed volume but take the shape of their container; particles are close but can move.
• Gases have no fixed shape or volume; particles are widely dispersed and move randomly.
• Plasma is an ionized gas at high temperatures, containing a significant number of electrons and positive ions.

Chemical Reactions

• A chemical reaction is a process that involves the rearrangement of atoms and molecules to form new substances.
• Reactants are the starting materials in a chemical reaction.
• Products are the substances formed as a result of a chemical reaction.
• Chemical equations represent chemical reactions using chemical formulas and symbols.
• Balancing chemical equations ensures that the number of atoms of each element is the same on both sides of the equation, obeying the law of conservation of mass.

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 of substance containing the same number of entities as there are atoms in 12 grams of carbon-12.
• Avogadro's number is approximately 6.022 x 10^23, representing the number of entities in one mole.
• Molar mass is the mass of one mole of a substance, expressed in grams per mole (g/mol).
• Limiting reactant is the reactant that is completely consumed in a chemical reaction, determining the maximum amount of product that can be formed.
• Percent yield is the ratio of the actual yield (amount of product obtained) to the theoretical yield (amount of product calculated based on stoichiometry), expressed as a percentage.

Chemical Bonding

• Chemical bonds are attractive forces that hold atoms together to form molecules and compounds.
• Ionic bonds are formed by the transfer of electrons between atoms, typically between a metal and a nonmetal, resulting in the formation of ions.
• Covalent bonds are formed by the sharing of electrons between atoms, typically between two nonmetals.
• Metallic bonds are formed by the delocalization of electrons among a lattice of metal atoms.
• Electronegativity is a measure of an atom's ability to attract electrons in a chemical bond.
• Polar covalent bonds occur when electrons are unequally shared between atoms due to differences in electronegativity, creating partial charges.
• Nonpolar covalent bonds occur when electrons are equally shared between atoms, typically when the electronegativity difference is small or zero.

Acids and Bases

• Acids are substances that donate protons (H+) or accept electrons.
• Bases are substances that accept protons or donate electrons.
• pH is a measure of the acidity or basicity of a solution, defined as the negative logarithm of the hydrogen ion concentration (pH = -log[H+]).
• Acidic solutions have a pH less than 7.
• Basic 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.
• Buffers are solutions that resist changes in pH upon addition of small amounts of acid or base, typically composed of a weak acid and its conjugate base or a weak base and its conjugate acid.

Organic Chemistry

• Organic chemistry is the study of carbon-containing compounds.
• Carbon's ability to form stable bonds with itself and other elements allows for the existence of a vast array of organic compounds.
• Hydrocarbons are organic compounds composed solely of carbon and hydrogen.
• Alkanes are saturated hydrocarbons containing only single bonds.
• Alkenes are unsaturated hydrocarbons containing at least one carbon-carbon double bond.
• Alkynes are unsaturated hydrocarbons containing at least one carbon-carbon triple bond.
• Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules.
• Alcohols contain a hydroxyl (-OH) group.
• Ethers contain an oxygen atom bonded to two alkyl or aryl groups (R-O-R').
• Aldehydes contain a carbonyl group (C=O) bonded to at least one hydrogen atom.
• Ketones contain a carbonyl group bonded to two alkyl or aryl groups.
• Carboxylic acids contain a carboxyl group (-COOH).
• Esters contain a carbonyl group bonded to an alkoxy group (-COOR).
• Amines contain a nitrogen atom bonded to one or more alkyl or aryl groups.
• Amides contain a carbonyl group bonded to a nitrogen atom.

Thermodynamics

• Thermodynamics is the study of energy and its transformations.
• Energy is the ability to do work or transfer heat.
• The first law of thermodynamics states that energy cannot be created or destroyed, only converted from one form to another (conservation of energy).
• The second law of thermodynamics states that the total entropy of an isolated system can only increase over time.
• Enthalpy (H) is a thermodynamic property that is the sum of the internal energy of a system plus the product of its pressure and volume.
• Entropy (S) is a measure of the disorder or randomness of a system.
• Gibbs free energy (G) is a thermodynamic potential that can be used to predict the spontaneity of a process under constant temperature and pressure conditions (G = H - TS).
• Exothermic reactions release heat (negative ΔH).
• Endothermic reactions absorb heat (positive ΔH).
• Spontaneous processes occur without external intervention (negative ΔG).
• Non-spontaneous processes require external intervention to occur (positive ΔG).

Kinetics

• Chemical kinetics is the study of reaction rates and the factors that affect them.
• Reaction rate is the change in concentration of reactants or products per unit time.
• Factors affecting reaction rates include temperature, concentration of reactants, surface area, and the presence of catalysts.
• Catalysts are substances that increase the rate of a chemical reaction without being consumed in the process, by providing an alternative reaction pathway with a lower activation energy.
• Activation energy is the minimum energy required for a chemical reaction to occur.
• Rate laws express the relationship between the rate of a reaction and the concentrations of reactants.
• Reaction order describes how the rate of a reaction is affected by the concentration of each reactant.

Equilibrium

• Chemical equilibrium is the state in which the rates of the forward and reverse reactions are equal, and the net change in concentrations of reactants and products is zero.
• Equilibrium constant (K) is the ratio of the concentrations of products to reactants at equilibrium, each raised to the power of their stoichiometric coefficients.
• 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.
• Factors that can shift equilibrium include changes in concentration, temperature, and pressure.