Two games, two different skills
Chemistry Freex trains recall: symbols, names, atomic numbers and the family each element belongs to. Molecule Freex moves on to compounds: which atoms a formula contains and how they are connected. Both are free, run in the browser on laptops, tablets and phones, and need no download and no account. Ads are never shown during play. Both games sit in the education category.
This guide lists what each game contains, taken from the games' own code, and points out where the drawings simplify the chemistry. Those simplifications make good discussion material in a classroom.
Chemistry Freex: what is in the deck
The deck has 55 cards: 44 elements, 6 alloys and 5 compounds. The elements are every one from 1 to 20 (hydrogen to calcium), then titanium (22), chromium (24), manganese to zinc (25 to 30), gallium (31), germanium (32), selenium (34), bromine (35), krypton (36), silver (47), tin (50), iodine (53), xenon (54), tungsten (74), platinum (78), gold (79), mercury (80), lead (82), bismuth (83) and uranium (92). The alloys are bronze, brass, electrum, duralumin, stainless steel and an aluminium-lithium alloy. The compounds are water, salt, carbon dioxide, ammonia and limestone, which is calcium carbonate.
Each card shows the symbol in large letters, the name underneath and the atomic number in the corner, with a colored bar for its family. There are 11 families: alkali metals, alkaline earth metals, transition metals, post-transition metals, the actinide uranium, non-metals, halogens, noble gases, metalloids, alloys and compounds.
How a question is built
At the start of each level, the game deals a board at random from the deck: 14 cards on level 1, two more per level, up to 28 from level 8. That board stays in place for the 8 questions of the level. For each question, the game picks one card on the board as the answer, then a question type:
- Elements get one of three types at equal odds: find it by name, say which element a symbol belongs to, or find the element with a given atomic number.
- Compounds get a name or a formula question, never a number, since they have no atomic number.
- Alloys only get name questions. They have no chemical symbol, so their card shows a plain label.
The same card can be the answer twice in one level. A question gives you 14.5 seconds on level 1, half a second less on each level after that, and 10 seconds from level 10 on. A correct answer scores 100, plus a speed bonus of up to 87 points on level 1, plus 20 for each answer already in your streak, and opens a fact card for 2.5 seconds. A wrong tap costs one of three lives and resets the streak, and the right card glows for 1.5 seconds so you can see where it was. A timeout also costs a life and moves straight on to the next question. Every run starts again at level 1.
Notes for the classroom
- Atomic number is the number of protons. The number in the corner of each element card is that count, which is why compounds and alloys have none.
- Odd symbols mostly come from Latin names: Na (natrium), K (kalium), Fe (ferrum), Ag (argentum), Sn (stannum), Au (aurum), Hg (hydrargyrum) and Pb (plumbum). W, for tungsten, comes from the metal's other name, wolfram.
- Hydrogen is colored as a non-metal. Most tables place it in group 1, above the alkali metals, but it is not one of them.
- Zinc and mercury carry the transition metal color. They are in the d-block and many textbooks call them transition metals, but under the strict IUPAC definition (an incomplete d sub-shell in the atom or in a common ion) they do not qualify. It is a clean example of a classification that depends on the definition you use.
- Alloys are mixtures, not compounds. Bronze is copper with tin, brass is copper with zinc and electrum is gold with silver, in proportions that can vary. Water, salt and limestone have fixed formulas.
Molecule Freex: the 41 formulas, in order
Each round shows a structure with empty slots, and a palette underneath that holds exactly the atoms the formula needs, with no spares. Drag each atom onto a slot marked with its element. Every formula has its own 30 second timer, and the run ends when one of them runs out. A finished formula scores its own points (60 for H₂, up to 300 for glycine) plus 6 points per second left, then shows a fact card for 3 seconds while the clock is stopped.
The order never changes, so a teacher can plan around it:
- 1 to 5: hydrogen H₂, hydrogen fluoride HF, oxygen O₂, nitrogen N₂, chlorine Cl₂.
- 6 to 11: water H₂O, hydrogen chloride HCl, sodium chloride NaCl, hydrogen peroxide H₂O₂, sodium fluoride NaF, potassium chloride KCl.
- 12 to 18: carbon dioxide CO₂, ammonia NH₃, methane CH₄, sulfur dioxide SO₂, nitrogen dioxide NO₂, hydrogen cyanide HCN, ozone O₃.
- 19 to 25: hydrogen sulfide H₂S, phosphine PH₃, sulfur trioxide SO₃, formaldehyde CH₂O, carbon tetrachloride CCl₄, nitric acid HNO₃, calcium chloride CaCl₂.
- 26 to 31: ethane C₂H₆, ethylene C₂H₄, acetylene C₂H₂, methanol CH₃OH, phosphoric acid H₃PO₄, sulfuric acid H₂SO₄.
- 32 to 35: acetic acid CH₃COOH, urea CO(NH₂)₂, propane C₃H₈, chloroform CHCl₃.
- 36 to 41: ethanol C₂H₅OH, glycine C₂H₅NO₂, silane SiH₄, nitrous oxide N₂O, hydrogen bromide HBr, iron(III) chloride FeCl₃.
After formula 41 the list starts again from hydrogen. The level number in the corner goes up every 3 formulas and stops at 7, which it reaches at formula 19. Across the whole list, 14 elements appear: H, C, N, O, F, Na, Si, P, S, Cl, K, Ca, Fe and Br. All of them are also in the Chemistry Freex deck, so the two games work well one after the other.
What the drawings simplify
The connections in every structure are right. In nitric, sulfuric and phosphoric acid, the hydrogens sit on oxygen atoms, not on the central atom. Ozone and nitrous oxide are drawn as chains, O-O-O and N-N-O. Ethanol has its oxygen between a carbon and a hydrogen. Three things are simplified, though:
- Every bond is drawn as one line. O₂ has a double bond, N₂ a triple bond, CO₂ two C=O double bonds, and HCN a triple bond between carbon and nitrogen. Ethylene has a C=C double bond and acetylene a triple one. Formaldehyde, acetic acid, urea and glycine each contain a C=O double bond.
- The drawings are flat. Methane is shown as a cross, but its four hydrogens point to the corners of a tetrahedron, 109.5 degrees apart. Ammonia is a low pyramid with angles near 107 degrees, water is bent at about 104.5 degrees, and CO₂ and HCN are straight lines.
- Four entries are ionic. Sodium chloride, sodium fluoride, potassium chloride and calcium chloride form crystals made of ions, not separate molecules. The line between Na and Cl stands for an ionic attraction inside a lattice.
One more detail for older students: glycine is drawn in its neutral form, H₂N-CH₂-COOH. In water and in the solid, it exists mostly as a zwitterion: a hydrogen moves from the acid group to the nitrogen, which gives the molecule a positive end and a negative end.
The atom colors follow the convention used by most molecular model kits: hydrogen white, carbon dark grey, oxygen red, nitrogen blue, sulfur yellow, chlorine green and phosphorus orange. Once students know them, they find the right atom in the palette without reading its letter.
A 20-minute class activity
This plan relies on the fixed order of Molecule Freex, so the whole class meets the same formulas in the same sequence.
- Minutes 0 to 2. Share the two links, gamefreex.com/game/elementeex and gamefreex.com/game/moleculeex. Nobody needs to sign up.
- Minutes 2 to 8. Chemistry Freex. Each student plays until their three lives are gone, and starts again if there is time left. Ask them to write down every card that glowed after a miss.
- Minutes 8 to 15. Molecule Freex. Each student notes the last formula number they reached. A student who completes every formula reaches formula 14, methane, within about 7 minutes even at the slowest pace, since each formula takes at most 30 seconds plus its 3 second fact card.
- Minutes 15 to 20. Discussion, using the list above: which of formulas 1 to 14 contain a double or triple bond (O₂, N₂ and CO₂), what methane looks like in three dimensions, and why table salt is not a molecule.
The cards missed in the first game make a short revision list for the next lesson. Scores only reach the leaderboards for signed-in players. Guests keep their best score in the browser, which is enough for one class session.