Fundamental Chemistry Concepts Summary & Study Notes

🧪 Atomic Structure

Atoms are composed of protons, neutrons, and electrons. Protons and neutrons reside in the nucleus; electrons occupy orbitals. The atomic number (Z) equals the number of protons; the mass number (A) equals protons plus neutrons. Isotopes differ by neutron count.

🔬 Periodic Table & Periodicity

The periodic table organizes elements by increasing atomic number. Groups (columns) share valence electron configurations and chemical properties. Periods (rows) indicate principal energy levels. Key trends: atomic radius decreases across a period and increases down a group; ionization energy and electronegativity increase across a period and decrease down a group.

🧬 Chemical Bonding

Ionic bonds form by electron transfer between metals and nonmetals (example: $NaCl$). Covalent bonds form by electron sharing between nonmetals (example: $H_2O$, $CH_4$). Polar covalent vs nonpolar covalent depends on electronegativity difference. Lewis structures, formal charge, and resonance help predict molecular structure.

📐 Molecular Geometry & Hybridization

Use VSEPR theory to predict molecular shapes from electron pair repulsion. Common geometries: linear, trigonal planar, tetrahedral, trigonal bipyramidal, octahedral. Hybridization (sp, sp2, sp3) explains bonding and geometry in many molecules.

⚖️ Stoichiometry & Chemical Reactions

Balanced chemical equations conserve mass and atoms. Convert between mass, moles, and molecules using molar mass and Avogadro's number: $N_A = 6.022\times10^{23}$. For mole conversions use fractions from the balanced equation: $\frac{mol:A}{mol:B}$. Example: moles = $\frac{mass}{molar:mass}$.

🚰 States of Matter & Intermolecular Forces

Solids, liquids, and gases differ by particle arrangement and movement. Intermolecular forces (IMFs) — London dispersion, dipole-dipole, and hydrogen bonding — determine boiling/melting points and solubility. Stronger IMFs generally increase boiling point and decrease vapor pressure.

🌡️ Thermochemistry & Thermodynamics

Enthalpy (ΔH) measures heat change at constant pressure. Exothermic reactions release heat (ΔH < 0); endothermic absorb heat (ΔH > 0). Entropy (ΔS) quantifies disorder. Gibbs free energy determines spontaneity: $\Delta G = \Delta H - T\Delta S$; spontaneous when ΔG < 0.

⚡ Chemical Kinetics

Reaction rate depends on reactant concentrations, temperature, catalyst presence, and surface area. Rate laws express rate as $rate = k[A]^m[B]^n$, where $k$ is the rate constant and orders m,n are determined experimentally. The activation energy (E_a) is the energy barrier for reaction; catalysts lower E_a.

⚖️ Chemical Equilibrium

At equilibrium the forward and reverse rates are equal. The equilibrium constant $K$ (or $K_c$, $K_p$) predicts the position of equilibrium. For a general reaction $aA + bB \rightleftharpoons cC + dD$, $K = \frac{[C]^c[D]^d}{[A]^a[B]^b}$. Le Chatelier's principle predicts shifts when conditions change.

💧 Acids, Bases & pH

Arrhenius, Bronsted-Lowry, and Lewis define acids/bases differently (proton donors/acceptors; electron pair acceptors/donors). pH = $-\log[H^+]$; pOH = $-\log[OH^-]$; $pH + pOH = 14$ at 25°C. Ka and Kb quantify acid/base strength; $pK_a = -\log K_a$.

🔋 Electrochemistry

Oxidation is loss of electrons; reduction is gain. Redox reactions transfer electrons; assign oxidation states to track electrons. Galvanic cells convert chemical energy to electrical energy; cell potential $E°${cell} = E°{cathode} - E°_{anode}. Electrolysis uses external voltage to drive nonspontaneous reactions.

🧪 Solutions & Colligative Properties

Concentration units: molarity (M = mol/L), molality (m = mol/kg), percent composition. Colligative properties (boiling point elevation, freezing point depression, osmotic pressure) depend on solute particle number: $\Delta T_b = iK_b m$, where $i$ is the van 't Hoff factor.

🧾 Analytical Techniques

Common methods: titration for concentrations, spectroscopy (UV-Vis, IR, NMR) for structure and concentration, chromatography for separation, and mass spectrometry for molecular mass and fragmentation patterns.

📊 Important Constants & Equations

• Avogadro's number: $N_A = 6.022\times10^{23}$.
• Ideal gas law: $PV = nRT$ (R = 0.08206 L·atm·mol^{-1}·K^{-1}).
• Rate law: $rate = k[A]^m[B]^n$.
• Gibbs free energy: $\Delta G = \Delta H - T\Delta S$.

These notes summarize key principles and equations. Use worked problems to reinforce calculations, practice balancing equations, and draw Lewis structures to master molecular geometry and bonding.