Browse Q&A by Concept
Select from the lists below to view frequently asked questions organized by concept.- Matter, Mass, and Volume
- Pure Substance
- Physical Properties
- Extensive and Intensive Properties
- States of Matter
- Physical Change
- Mixture
- Homogeneous Mixture
- Heterogeneous Mixture
- Separating Mixtures
- Element
- Compound
- Chemical Reaction
- Chemical Change
- Chemical Symbols and Formulas
- Chemical Properties and Chemical Reactions
- Reactants and Products
- Recognizing Chemical Reactions
- SI Base Units
- Metric Prefixes
- Scientific Notation
- Length and Volume
- Mass and Weight
- Kinetic Energy
- Temperature and Temperature Scales
- Dimensional Analysis
- Metric Unit Conversions
- Derived Units
- Density
- Accuracy and Precision
- Percent Error
- Measurement Uncertainty
- Rounding
- Significant Figures
- Significant Figures in Addition and Subtraction
- Significant Figures in Multiplication and Division
- Democritus' Idea of the Atom
- Law of Conservation of Mass
- Law of Multiple Proportions
- Law of Definite Proportions
- Mass Ratio Calculation
- Dalton's Atomic Theory
- Atom
- Electron
- Proton
- Neutron
- Cathode Ray Tube
- Oil Drop Experiment
- Plum Pudding Atomic Model
- Gold Foil Experiment
- Atomic Nucleus
- Atomic Number
- Mass Number
- Isotope
- Atomic Mass Unit
- Calculating Average Atomic Mass
- Electromagnetic Spectrum
- Wavelength and Frequency Calculations
- Quantization of Energy
- Photoelectric Effect
- Atomic Emission Spectra
- Bohr's Atomic Model
- Spectral Lines of Hydrogen
- de Broglie Wave Equation
- Quantum Mechanics
- Heisenberg Uncertainty Principle
- Quantum Mechanical Atomic Model
- Energy Level
- Orbital
- Quantum Numbers
- Aufbau Principle
- Pauli Exclusion Principle
- Hund's Rule and Orbital Filling Diagrams
- Electron Configurations
- Valence Electrons
- Noble Gas Configuration
- Early History of the Periodic Table
- Mendeleev's Periodic Table
- Periodic Law
- Modern Periodic Table
- Metals
- Nonmetals
- Metalloids
- Blocks of the Periodic Table
- Hydrogen and Alkali Metals
- Alkaline Earth Metals
- Noble Gases
- Halogens
- Transition Metals
- Lanthanides and Actinides
- Periodic Trends: Atomic Radius
- Ion
- Periodic Trends: Ionization Energy
- Electron Shielding
- Periodic Trends: Electron Affinity
- Periodic Trends: Ionic Radii
- Periodic Trends: Electronegativity
- Periodic Trends: Metallic and Nonmetallic Character
- Molecular Formula
- Empirical Formula
- Cation
- Anion
- Transition Metal Ions
- The Stock System of Nomenclature
- Naming Binary Ionic Compounds
- Formulas for Binary Ionic Compounds
- Polyatomic Ions - Naming and Formulas
- Ternary Ionic Compounds - Naming and Formulas
- Binary Molecular Compounds - Naming and Formulas
- Acids - Naming and Formulas
- Bases - Naming and Formulas
- Chemical Bond
- Covalent Bond
- Molecular Compounds
- Energy and Covalent Bond Formation
- Lewis Electron-Dot Structures
- Single Covalent Bonds
- Multiple Covalent Bonds
- Coordinate Covalent Bond
- Covalent Bonding in Polyatomic Ions
- Resonance
- Exceptions to the Octet Rule
- Bond Energy
- VSEPR Theory
- Molecular Shapes: No Lone Pairs on Central Atom
- Molecular Shapes: Lone Pair(s) on Central Atom
- Bond Polarity
- Polar Molecules
- Van der Waals Forces
- Hydrogen Bonding
- Physical Properties and Intermolecular Forces
- Valence Bond Theory
- Hybrid Orbitals - sp3
- Hybrid Orbitals - sp and sp2
- Sigma and Pi Bonds
- Avogadro's Number
- Conversions Between Moles and Atoms
- Molar Mass
- Conversions Between Moles and Mass
- Conversions Between Mass and Number of Particles
- Avogadro's Hypothesis and Molar Volume
- Conversions Between Moles and Gas Volume
- Gas Density
- Mole Road Map
- Percent Composition
- Percent of Water in a Hydrate
- Determining Empirical Formulas
- Determining Molecular Formulas
- Kinetic Molecular Theory
- Gas Pressure
- Atmospheric Pressure
- Pressure Units and Conversions
- Average Kinetic Energy and Temperature
- Surface Tension
- Evaporation
- Vapor Pressure
- Boiling
- Vapor Pressure Curves
- Melting
- Sublimation
- Crystal Systems
- Unit Cells
- Classes of Crystalline Solids
- Amorphous Solid
- Change of State
- Heating and Cooling Curves
- Phase Diagrams
- Phase Diagram for Water
- Compressibility
- Factors Affecting Gas Pressure
- Boyle's Law
- Charles's Law
- Gay-Lussac's Law
- Combined Gas Law
- Avogadro's Law
- Ideal Gas Law
- Calculating the Molar Mass of a Gas
- Gas Stoichiometry
- Real and Ideal Gases
- Dalton's Law of Partial Pressures
- Mole Fraction
- Gas Collection by Water Displacement
- Diffusion, Effusion, and Graham's Law
- Solution
- Solute-Solvent Combinations
- Rate of Dissolving
- Saturated and Unsaturated Solutions
- Solubility
- Supersaturated Solutions
- Henry's Law of Solubility
- Percent Solutions
- Molarity
- Molality
- Preparing Solutions
- Dilution
- Vapor Pressure Lowering
- Freezing Point Depression
- Boiling Point Elevation
- Electrolytes and Colligative Properties
- Calculating Molar Mass Using Colligative Properties
- Molecular and Ionic Equations
- Net Ionic Equation
- Predicting Precipitates Using Solubility Rules
- Chemical Potential Energy
- Heat
- Exothermic Reaction
- Endothermic Reaction
- Exothermic and Endothermic Processes
- Heat Capacity and Specific Heat
- Specific Heat Calculations
- Enthalpy
- Calorimetry
- Thermochemical Equation
- Stoichiometry and Thermochemical Equations
- Heats of Fusion and Solidification
- Heats of Vaporization and Condensation
- Multi-Step Problems with Changes of State
- Heat of Solution
- Hess's Law of Heat Summation
- Heat of Combustion
- Standard Heat of Formation
- Heat of Reaction
- Reaction Rate
- Collision Theory
- Activation Energy
- Potential Energy Diagrams
- Activated Complex
- Factors Affecting Reaction Rate
- Catalyst
- Rate Law and Rate Constant
- Reaction Order
- Determining the Rate Law from Experimental Data
- Reaction Mechanisms and the Elementary Step
- Reaction Intermediate
- Molecularity
- Rate-Determining Step
- Reaction Mechanisms and Potential Energy Diagrams
- Reversible Reaction
- Chemical Equilibrium
- Equilibrium Constant (Keq)
- Calculations with Equilibrium Constants
- Nonreversible Reactions
- Le Châtelier's Principle
- Effect of Concentration
- Effect of Temperature
- Effect of Pressure
- Le Châtelier's Principle and the Equilibrium Constant
- Solubility Product Constant (Ksp)
- Calculating Solubility from Ksp
- Calculating Ksp from Solubility
- Predicting Precipitates
- Common Ion Effect
- Acid
- Base
- Arrhenius Acids
- Arrhenius Bases
- Brønsted-Lowry Acids and Bases
- Brønsted-Lowry Acid-Base Reactions
- Lewis Acids and Bases
- Self-Ionization of Water (Kw)
- pH
- Calculating pH
- pOH Scale and Calculations
- Strong and Weak Acids and Acid Ionization Constant (Ka)
- Strong and Weak Bases and Base Ionization Constant (Kb)
- Calculating Ka and Kb
- Calculating pH of Weak Acid and Base Solutions
- Neutralization Reaction and Net Ionic Equations
- Titration Experiment
- Titration Calculations
- Titration Curves
- Indicators
- Salt Hydrolysis
- Calculating pH of Salt Solutions
- Buffers
- Oxygen in Reactions
- Redox Reactions and Ionic Compounds
- Redox Reactions and Molecular Compounds
- Oxidizing and Reducing Agents
- Corrosion
- Assigning Oxidation Numbers
- Oxidation-Number Changes in Reactions
- Identifying Redox Reactions
- Balancing Redox Reactions: Oxidation Number Change Method
- Balancing Redox Reactions: Half-Reaction Method
- Balancing Redox Reactions: Half-Reaction Method in Basic Solution
- Radioactivity
- Types of Radioactive Decay
- Half-Life
- Nuclear Fission
- Nuclear Fusion
- Nuclear Power
- Detection of Radioactivity
- Background Radiation
- Penetrating Ability of Emissions
- Effects of Radiation
- Radioisotopes in Medical Diagnosis and Treatment
- PET Scan
- Conservation of Mass and Energy in Nuclear Reactions
- Organic Chemistry Overview
- Hydrocarbon
- Straight-Chain Alkanes
- Branched Alkanes
- Alkenes and Alkynes
- Structural Isomers and Stereoisomers
- Cyclic Hydrocarbons
- Aromatic Hydrocarbons
- Alcohols
- Ethers
- Aldehydes and Ketones
- Carboxylic Acids
- Esters
- Amines
- Alkyl Halides
- Substitution Reactions
- Addition Reactions
- Oxidation Reactions
- Condensation Reactions
- Polymerization - Addition Polymers
- Polymerization - Condensation Polymers