Atomic Structure and Chemical Bonding

Atomic Structure

• Atoms are the fundamental building blocks of matter.
• Atoms consist of a positively charged nucleus containing protons and neutrons, surrounded by negatively charged electrons.
• Protons have a positive charge, neutrons are neutral, and electrons have a negative charge.
• The number of protons defines the element.
• Atomic number is the number of protons in an atom.
• Atomic mass is the total mass of protons and neutrons in an atom.
• Isotopes are atoms of the same element with different numbers of neutrons.
• Electrons orbit the nucleus in specific energy levels, or shells.
• The first shell can hold a maximum of two electrons, the second shell can hold eight, and so on.
• Valence electrons are the electrons in the outermost shell and determine an element's chemical properties.

Chemical Bonding

• Chemical bonds are forces that hold atoms together in molecules or compounds.
• Ionic bonds form between metals and nonmetals, where one atom donates electrons to another, creating oppositely charged ions that attract each other.
• Covalent bonds form between nonmetals when atoms share electrons to achieve a stable electron configuration.
• Metallic bonds occur between metal atoms, in which electrons are delocalized and shared amongst many atoms.
• Hydrogen bonds are a special type of dipole-dipole attraction between a hydrogen atom bonded to a highly electronegative atom (often oxygen or nitrogen) and another electronegative atom.
• Intermolecular forces are attractions between molecules that are weaker than bonds between atoms.

Chemical Reactions

• Chemical reactions involve the rearrangement of atoms to form new substances.
• Reactants are the substances that undergo change.
• Products are the new substances formed.
• Chemical equations represent chemical reactions; they show the reactants and products.
• The law of conservation of mass states that mass is neither created nor destroyed in a chemical reaction.
• Chemical reactions can be categorized by different types, such as synthesis, decomposition, single replacement, double replacement, and combustion.
• The rate of a reaction can be affected by various factors, including temperature, concentration, surface area, and catalysts.

States of Matter

• Matter exists in three primary states: solid, liquid, and gas.
• Solids have a fixed shape and volume due to strong intermolecular forces holding particles in a fixed arrangement.
• Liquids have a definite volume but take the shape of their container due to weaker intermolecular forces allowing particles to move past one another.
• Gases have neither a fixed shape nor volume; particles are widely dispersed and move randomly.
• Phase transitions involve changes between these states (e.g., melting, boiling, freezing, sublimation).
• Changes in temperature and pressure affect the state of matter.

Solutions

• Solutions are homogeneous mixtures of two or more substances.
• The solute is the substance being dissolved.
• The solvent is the substance doing the dissolving.
• Solubility is the ability of a substance to dissolve in a solvent.
• Factors affecting solubility include temperature, pressure, and nature of the solute and solvent.
• Concentration expresses the amount of solute in a given amount of solvent or solution. Different units can express this (e.g., molarity, molality, percent by mass).

Acids and Bases

• Acids are substances that donate protons (H+ ions) in an aqueous solution.
• Bases are substances that accept protons (H+ ions) in an aqueous solution.
• The pH scale measures the acidity or basicity of a solution.
• Acids have a pH less than 7, bases have a pH greater than 7, and neutral solutions have a pH of 7.
• Strong acids and bases completely dissociate in water, while weak acids and bases only partially dissociate.
• Neutralization reactions occur when an acid reacts with a base to form a salt and water.

Stoichiometry

• Stoichiometry is the calculation of quantitative relationships between reactants and products in a chemical reaction.
• Stoichiometric calculations use balanced chemical equations to determine amounts of reactants and products.
• Molar ratios from balanced equations are crucial to predict and calculate the quantities involved.

Thermodynamics

• Thermodynamics is the study of energy and its transformations.
• Concepts like enthalpy (heat content), entropy (disorder), and free energy (spontaneity) explain the direction and feasibility of chemical processes.
• First law states energy can be neither created nor destroyed.
• Second law indicates that the total entropy of an isolated system can only increase over time.
• Third law describes the behavior of systems as temperature approaches absolute zero.

Kinetics

• Chemical kinetics studies the rates of chemical reactions.
• Reaction rates are influenced by factors like temperature, concentration, and presence of catalysts.
• Collision theory describes how molecules must collide with sufficient energy and proper orientation to form products.
• Rate laws describe the relationship between the reaction rate and the concentrations of reactants.
• Activation energy is the minimum energy needed for a reaction to proceed.