chemistry

Browse all 118 chemical elements →

• Atomic Mass and Isotopes: A Weighted-Average Calculator

  Type in your own isotope masses and abundances to get the weighted average, work backwards from an average to the abundances, or find which element an atomic mass belongs to.

• Balancing Chemical Equations

  Set the coefficients on a real reaction and watch a live atom tally check both sides. Learn why every element must balance (conservation of mass) with steppers and a 'Show me' answer.

• Bond Polarity: How to Tell if a Bond Is Polar or Nonpolar

  Subtract the two electronegativities to get ΔEN, then read off the bond type. A chart of 30 bonds sorted by polarity, what δ+ and δ− mean, and why polar bonds can still make a nonpolar molecule.

• Electron Configuration Builder

  Pick any element from hydrogen to krypton and watch its ground-state electron configuration and Bohr shell diagram build up in Aufbau order, including the chromium and copper exceptions.

• Interactive Bohr Model: Atomic Shell Diagram Builder

  Build the Bohr model of any element (Z 1-118). Pick an atomic number to see the nucleus and electron shells fill, with electrons-per-shell and outer-shell count.

• Interactive Periodic Table

  Explore all 118 elements in an interactive periodic table: recolor by category, state, or block, and open any element for its electron configuration, Bohr model, and uses.

• Ionic vs Covalent Bonds (and Metallic)

  Pick two elements and compare their electronegativity. The ΔEN difference predicts an ionic, covalent (polar or nonpolar), or metallic bond.

• Lewis Dot Structures

  Draw the Lewis dot structure of common molecules. See bonds as lines, lone pairs as dots, count valence electrons, and meet the octet-rule exceptions.

• Mole Ratio Calculator: Stoichiometry Step by Step

  Read the mole ratio straight off the balanced coefficients, then use it to hop from any substance to any other. A table of 57 ratios for 13 common reactions, and a grams-to-grams calculator.

• Molecular Geometry: The Full VSEPR Shapes Chart

  Every VSEPR shape in one chart, with electron geometry, bond angles, hybridization and AXE notation. Look a shape up by molecule, or by counting bonds and lone pairs.

• Molecule Builder: Build Molecules Atom by Atom

  A free build-a-molecule sandbox: tap atoms into the tray, bond them, and watch real molecules snap together. 42 to discover, and it tells you when you are close.

• Noble Gases: Group 18 of the Periodic Table

  Group 18 is the noble gases: helium, neon, argon, krypton, xenon, radon and oganesson. All seven with their notation, boiling points and glow colours, and why a full outer shell stops them reacting.

• Periodic Table Game: Find and Memorize the Elements

  A free periodic table memorization game. Drill the first 20, a single family, or all 118: every element you miss comes back until you place it right. No signup.

• Periodic Trends: The Electronegativity Trend and Map

  The electronegativity trend in actual numbers, a colour map of all 118 elements by electronegativity, ionization energy or electron affinity, and what each trend does and why.

• States of Matter: The Heating Curve, Phase Changes, and Latent Heat

  Add heat to ice and watch it melt then boil on a live heating curve: the temperature plateaus at 0 and 100 °C while energy breaks bonds. Covers the states, phase changes, and latent heat.

• The Gas Laws: Formulas, Graphs, and Worked Examples

  Every gas law with its formula, its graph and a worked example: Boyle's, Charles's, Gay-Lussac's, Avogadro's, Dalton's, Graham's, the combined law and PV = nRT, plus R in six sets of units.

• The Mole: Converting Between Mass, Moles and Particles

  Convert mass to moles, moles to mass, or either to a number of particles, for any formula you type. Molar masses are added up atom by atom with the arithmetic shown.

• The Particle Box: Kinetic Molecular Theory

  Heat, squeeze, and cool a live box of atoms to watch pressure, the speed distribution, and even melting and boiling emerge from the collisions. Kinetic theory you can play with.

• The pH Scale: Acid and Base Ranges, Values and Examples

  Which pH values count as acids and which as bases, what every number from 0 to 14 means, the pH of common substances, and a calculator linking pH, pOH, [H⁺] and [OH⁻].

• Types of Chemical Reactions

  Classify reactions as synthesis, decomposition, single replacement, double replacement, or combustion, then use each pattern to predict the products.

• Valence Electrons & Lewis Dot Symbols

  Valence electrons for every column of the periodic table, the Lewis dot symbol for each main group, and how to add up the valence electrons of a whole molecule.