50 Must-Know Chemistry Terms (with Examples)

e.g. A single gold atom is still gold; you can't divide it further with chemistry.

e.g. Carbon has 6 protons. Always. That's what makes it carbon.

e.g. Carbon-12 has 6 neutrons. Carbon-14 has 8 — same element, different isotope.

e.g. Hydrogen has 1 electron. Sodium has 11. Electrons drive almost all chemistry.

e.g. Iron has atomic number 26 — meaning 26 protons.

e.g. Carbon-14 has a mass number of 14 (6 protons + 8 neutrons).

e.g. Hydrogen, deuterium, and tritium are all isotopes of hydrogen.

e.g. Sodium losing one electron becomes Na⁺. Chlorine gaining one becomes Cl⁻.

e.g. Ca²⁺ in bones, K⁺ in your nerves.

e.g. Cl⁻ in salt, OH⁻ in soap.

e.g. Iron, oxygen, gold, neon — all elements.

e.g. Group 1 = alkali metals. Group 18 = noble gases.

e.g. Period 2 has 8 elements. Period 6 has 32.

e.g. Iron, copper, gold, sodium, mercury are all metals.

e.g. Oxygen, nitrogen, sulfur, chlorine — all nonmetals.

e.g. Silicon makes up computer chips because it's a semiconductor.

e.g. Chlorine in pools. Fluorine in toothpaste. Iodine in salt.

e.g. Helium balloons, neon signs, argon in incandescent bulbs.

e.g. Iron, copper, silver, gold all live here.

e.g. Neodymium magnets in your headphones, europium in TV phosphors.

e.g. The bond between H and O in water is what makes water a single molecule.

e.g. Na⁺ and Cl⁻ in table salt are held together by electrostatic attraction.

e.g. The two H–O bonds in water are covalent.

e.g. In water, oxygen pulls harder on the shared electrons than hydrogen does.

e.g. Fluorine has the highest electronegativity (3.98). Cesium has one of the lowest (0.79).

e.g. H₂O, CO₂, O₂ — all molecules.

e.g. Water (H₂O) is a compound. Pure oxygen (O₂) is not.

e.g. The water Lewis structure has 2 lone pairs on oxygen and 2 bonds to hydrogen.

e.g. Carbon has 4 valence electrons, so it forms 4 bonds.

e.g. Oxygen needs 2 more electrons to reach 8 — that's why H₂O exists.

e.g. 2H₂ + O₂ → 2H₂O is a reaction (combustion of hydrogen).

e.g. In burning wood, the wood and the oxygen in the air are reactants.

e.g. Burning wood produces CO₂ and water vapor as products.

e.g. In 2H₂ + O₂ → 2H₂O, the coefficient on H₂O is 2.

e.g. Conservation of mass — atoms aren't created or destroyed.

e.g. 1 mole of carbon weighs 12 grams.

e.g. Water has a molar mass of 18 g/mol (2 × 1 + 16).

e.g. If you have 2 moles of H₂, you need 1 mole of O₂ to make 2 moles of water.

e.g. If you have 5 buns and 10 burgers, buns are the limiting reagent.

e.g. Platinum catalyzes the reactions in your car's catalytic converter.

e.g. Ice, iron, salt.

e.g. Water, mercury, ethanol.

e.g. Oxygen, nitrogen, helium.

e.g. Lightning, the Sun, neon signs.

e.g. Salt water, brass, air.

e.g. In salt water, salt is the solute.

e.g. In salt water, water is the solvent.

e.g. Seawater is about 3.5% salt by mass.

e.g. Pure water has a pH of 7. Lemon juice is around 2.

e.g. HCl, vinegar (acetic acid), citric acid.