First of all, this game I wish I had this when I was studying chemistry in school XD
The Good:
* The minimalist art helps a lot to give character to this game. It makes the gameplay of the Periodic Table system easier visually because of its simple art style.
* The core idea of it is very new in my eyes. It is a fresh casual game that does not give me any stress but rather helps me to learn while playing.
* The music and SFX are all on point. It helps the game to be more lovely.
* I love the trivia or the chemical descriptions showing in the game.
* The game is well-polished.
The Bad (actually, things that can be improved):
* Add a simple description for the effect cards. Or maybe at least a card name to them so I know at the start that I know, what will be the effect of these special cards. Also, make it a lighter, more vibrant color, to show that these Special Effect cards are not the typical periodic table cards but have effects that can change the path of your gameplay experience.
* There is a time that I just keep on throwing my cards to get the card I need. It burns a lot of time for me. It is not skill-related but luck-related. Somehow it causes a little stress to me because I don't have anything to do just throw cards and believe in the heart of the cards (yugioh meme XD). I have suggestions for this down below.
* It is kind of annoying when I accidentally drop cards and now they will combine and create a new element but I don't need that. Sadly, I don't have any way to separate them even if it is accidentally. For me, it is kind of a heavily punishable feature too, especially for this time-based game.
My suggestions:
* If your plan is just to make this game just a casual game, I respect that. But if you want to add more possibilities for this game, add a progression system. Maybe level-based or a story. I even think you can add a roguelike system to this game. Make the card-building progression-based so it will now be a deck-building game. It will help players to be more strategic in every move they make.
* Instead of throwing a single card to spawn a new single card. Maybe you want to consider adding a shuffle system. Or replace my whole hand with a new set of cards. This will help me to think more than base it on my luck. For example, I have very good cards in my hand but I don't need them all for now, I can't progress to the game if I do not get this specific card. So what will I do, should I gamble all my hand cards or should I maybe just combine cards so it can open a new slot in my hand?
* You can also consider adding a card effect to the game based on the card that I combined. Here are some crazy ideas. like for example, I can combine cards to create Chlorine, then I can use that Chlorine to melt some cards because Chlronine can be used to melt some stuff, or I can combine cards to create Einsteinium and then Einstein will spawn in the game to freeze the time haha or I can create an element that can create a bomb that will clear the whole board haha. Sorry, my game design hunger is going crazy for this game. XD
Overall, this game is a very bright game idea that has a huge potential not just for players who want to chill but also for students to help them study Chemistry in a fun way.
Looking forward for your game! See you in Brazil :)