Basic Chemistry for Engineers — Definition of an Element What do we call substances that have not yet been resolved into any simpler substances by chemical means and are regarded as fundamental in composition?

Introduction:
Engineers routinely encounter material classifications. Knowing the difference between elements, compounds, atoms, and molecules is essential for material selection, combustion calculations, and corrosion analysis. This question focuses on the foundational definition of an element.

Given Data / Assumptions:

• Chemical decomposition methods (e.g., electrolysis, thermal decomposition) are considered.
• Modern periodic table context is implied.
• Macroscopic samples comprised of a single chemical species are under consideration.

Concept / Approach:
An element is a pure substance consisting of only one type of atom; it cannot be chemically broken down into simpler substances. Compounds are chemical combinations of two or more elements in fixed proportions. Atoms are the smallest units of elements that retain chemical identity. Molecules are assemblies of atoms bonded together; they can be elemental (e.g., O2) or compound (e.g., H2O).

Step-by-Step Solution:
Identify the phrase “cannot be resolved into simpler substances by chemical means.”Match to the definition of “element,” not to “compound,” “atom,” or “molecule.”Therefore, the correct term is “elements.”

Verification / Alternative check:
Examples: Copper, sulfur, and oxygen are elements; water (H2O) is a compound of hydrogen and oxygen; O2 is a molecular form of the element oxygen.

Why Other Options Are Wrong:
Compounds can be chemically decomposed into elements; atoms are submicroscopic units, not macroscopic substances; molecules denote bonded groups, not necessarily irreducible substances.

Common Pitfalls:
Equating “molecule” with “element”; forgetting that some elemental species are monatomic (e.g., noble gases) while others are diatomic (e.g., N2, O2).

Final Answer:
elements