Elemental Magic. Alchemy. Elementalism
Elemental Magic is magic that deals with the elements and matter.
Alchemy belongs to Elemental Magic in the Magic Book. Alchemy is magical practice of transmutation of energy. It is about changing structure of material, transforming stuff on elemental level.

There are Substances (or materials, elements) and Processes. Processes are the heart of Alchemy. There are many Alchemical Processes, which include Distillation, Fermentation, Calcination, Fusion, Grinding, Ignition, Melting, Precipitation, etc. These are processes that deal with the change (transmutation) of elements. Here's a list of alchemical processes for example – http://www.levity.com/alchemy/alch-pro.html. Important to note that Alchemy is spiritual practice and all magic practice is spiritual. The change can be applied to person, as in Magnum opus.
Substances
Matter – substances, elements, materials. Substance is matter with constant chemical composition. It can be solid, liquid, gas or plasma (corresponding to four elements in Elementalism).
Processes
Describe the different types of change that may happen to matter.
Also for practice you need Equipment and Laboratory.
Search for Pure Elements
Search for pure elements led to Chemistry, which took a deeper dive into the study of pure elements. The techniques used in Alchemy helped shape some sciences, most importantly of course Chemistry and Chemistry in reverse is helpful for the practitioner of Alchemy today. The difference is in the process or even purpose of the practice. Alchemy is magic (personal and spiritual practice), while chemistry is science (based on objective observation). Both are awesome.
The central symbols of the alchemical texts play around with elements and substances. Below are several lists (systems) of the first discovered elements and substances that are important in alchemy.
Four Elements: Fire, Water, Earth, Air
Seven Planetary Metals: Gold – Sol, Silver – Luna, Copper – Venus, Iron – Mars, Tin – Jupiter, Quicksilver – Mercury, Lead – Saturn
Substances can be classified by their general structure of composition. Some common substances include Salt, Oil, Alcohol, Metal, Wood, Acids and Bases, etc. This is probably my preferred way of classifying materials in alchemy. Some substances can be pure while others compound elements and still fall into the same category. Like Tin and Tin-Copper alloy are both metals.

Elementalism
Elementalism is magical practice that deals with the (4) basic elements. I like to think of elementalism as categorical, but the power of the basic elements is available to the practicing magician. One idea in Elementalism is that any thing or system can be divided into 4 basic elements. These basic elements entail the powers that they have. Powers of the elements are natural powers, while power of transmutation is derived power from the elements. Elementalism attempts more direct control over the elements or a more direct way of contact with the elements.