SDSU Chemistry Placement Practice Test 2025 – The Comprehensive All-in-One Guide to Exam Success!

A substance that cannot be separated into simpler substances by chemical means is defined as an element. Elements are the most basic forms of matter, consisting of atoms that share the same atomic number, meaning they have the same number of protons in their nuclei. Because they cannot be broken down into simpler substances, elements represent the fundamental building blocks of all matter.

In contrast, compounds are substances formed when two or more elements chemically bond together in fixed ratios, and they can be separated into their constituent elements through chemical reactions. Mixtures consist of two or more substances that are physically combined and can be separated by physical means, such as filtration or distillation. Solutions are a type of homogeneous mixture where one substance (the solute) is dissolved in another (the solvent), and these can also be separated into their components through physical processes. Understanding these distinctions is key to recognizing why an element is unique in its inability to be decomposed into simpler substances.