For all the students who are studying chemistry in their schools, ACD ChemSketch is a really nice tool to play with. It allows you to draw the chemical structures of all the possible organic molecules you can think of. You start with basic compounds such as CH4 (methane gas) and keep adding new atoms and molecules it until you get the desired target molecule. Not only you can draw 2D molecular structure diagrams of any chemicals, you can also rotate them and view their 3D arrangement easily.
ACD ChemSketch is a comprehensive software package that comes with many advanced tools, for example, it can calculate the properties of the molecules you have drawn, it can tell you possible known names of the drawn molecules and so on. It is used by many corporations and also government departments to analyze chemical compounds. But all the advanced features are available only in the paid commercial version. For students, such advanced features are not really needed and even without them it is great software to help you understand the chemical structures of various compounds.
One of the features that high school students are going to love is the interactive atomic table. You can view all the elemetns in the atomic table in many different styles, by their electronic configurations, by their state (gas, solid, liquid), whether they are metal or non-metal, and more. When you select an element, it shows its properties and history. It even displays a picture of the element if available.
It is a great software for all the chemistry students, as it allows you to play with chemical structures without actually being in a chemistry laboratory. All the chemical structure you draw, it can name them perfectly well using an integrated IUPAC naming add-on which makes it a handy tool to find the names of certain compounds whether they are organic, organometallic or polymers.
You can download ACD ChemSketch from https://www.acdlabs.com/resources/freeware/chemsketch/download.php.