Atomic Structure and Chemical Bonding

Atomic Structure

• Atoms are the fundamental building blocks of matter.
• Atoms consist of a nucleus containing protons and neutrons, and electrons orbiting the nucleus.
• Protons have a positive charge, electrons have a negative charge, and neutrons have no charge.
• The number of protons in an atom defines its atomic number and determines the element.
• Different isotopes of an element have the same number of protons but varying numbers of neutrons.
• Atomic mass is the weighted average mass of all isotopes of an element.
• Electrons occupy specific energy levels or shells around the nucleus.
• Each shell can hold a maximum number of electrons.
• The arrangement of electrons in the different energy levels determines the chemical properties of an atom.

Chemical Bonding

• Chemical bonds hold atoms together in molecules or compounds.
• Ionic bonds form between metals and nonmetals, where one atom donates electrons to another.
• Covalent bonds form between nonmetals, where atoms share electrons.
• Metallic bonds occur within metals, where electrons are delocalized and shared by all atoms.
• Hydrogen bonds are a special type of dipole-dipole interaction, characterized by attraction between a hydrogen atom bonded to a highly electronegative atom (like oxygen or nitrogen) and another electronegative atom.
• Van der Waals forces are weak intermolecular forces that arise from temporary fluctuations of electron distribution.

States of Matter

• Matter exists in three primary states: solid, liquid, and gas.
• Solids possess a fixed shape and volume due to strong intermolecular forces.
• Liquids have a definite volume but take the shape of their container due to weaker intermolecular forces than solids but stronger than gases.
• Gases have neither a fixed shape nor a fixed volume.
• Phase transitions occur when matter changes between these states e.g., melting, freezing, vaporization, condensation, sublimation, deposition.

Periodic Table

• The periodic table organizes elements based on their atomic number and chemical properties.
• Elements are arranged in rows (periods) and columns (groups).
• Elements within the same group share similar chemical properties because they have the same number of valence electrons.
• Trends in properties, such as atomic radius, ionization energy, and electronegativity, are observed across periods and groups.

Chemical Reactions

• Chemical reactions involve the rearrangement of atoms to form new substances (products) from existing ones (reactants).
• Chemical equations represent chemical reactions, with reactants on the left and products on the right.
• The law of conservation of mass dictates the number of atoms of each element must be equal on both sides.
• Reactions can be classified into different types e.g., synthesis, decomposition, single displacement, double displacement, combustion, neutralization.
• Reaction rates are influenced by factors like temperature, concentration, surface area, and catalysts.

Solutions

• Solutions are homogeneous mixtures of two or more substances, where one component (solute) is dissolved in another component (solvent).
• Solubility refers to the maximum amount of solute that can dissolve in a given amount of solvent at a specific temperature and pressure.
• Solutions can be saturated, unsaturated, or supersaturated.
• Concentration expresses the relative amount of solute in a solution.
• Molarity is a common way to express concentration in terms of moles of solute per liter of solution.
• Colligative properties (e.g boiling point elevation and freezing point depression) depend on the concentration of solute particles, not their identity.

Acids and Bases

• Acids and bases are chemical compounds that ionize in water to produce hydrogen ions (H⁺) and hydroxide ions (OH^-), respectively.
• The pH scale measures the acidity or basicity of a solution, with a scale ranging from 0 to 14.
• Acids generally have a pH less than 7, bases greater than 7, and neutral solutions have a pH of 7.
• Strong acids and bases completely ionize in water, whereas weak acids and bases only partially ionize.
• Neutralization reactions occur when acids and bases react to form water and a salt.

Stoichiometry

• Stoichiometry is the quantitative relationship between reactants and products in a chemical reaction.
• The balanced chemical equation provides information about the mole ratios of reactants and products.
• Moles relate the mass of a substance to the number of atoms or molecules present.
• Stoichiometric calculations allow the determination of quantities of reactants and products involved in a reaction.

Thermodynamics

• Thermodynamics deals with energy transformations in chemical reactions.
• Enthalpy (H) measures the heat content of a system.
• Entropy (S) measures the disorder or randomness in a system.
• Free energy (G) determines the spontaneity of a reaction at a constant temperature and pressure.
• The change in enthalpy, entropy, and free energy provide insights into the energy and direction of a chemical reaction.

Redox Reactions

• Redox reactions involve electron transfer between reactants.
• Oxidation is the loss of electrons, and reduction is the gain of electrons.
• Oxidizing agents cause oxidation and are themselves reduced.
• Reducing agents cause reduction and are themselves oxidized.
• Balancing redox reactions often involves half-reaction method.