Carbon dioxide (CO2) is a compound because it contains two different elements — carbon and oxygen — chemically bonded together. Oxygen gas is a molecule but contains only one element. Gold and helium are single elements.
Question 2 True / False
A compound can be separated into its elements by filtering.
TTrue
FFalse
Answer: False
Filtering is a physical separation method that works for mixtures but not compounds. Because the atoms in a compound are held together by chemical bonds, only a chemical change (like electrolysis or a chemical reaction) can break a compound into its component elements.
Question 3 Short Answer
Explain why water (H2O) is classified as a compound rather than an element.
Think about your answer, then reveal below.
Model answer: Water contains two different elements — hydrogen and oxygen — chemically bonded together in a fixed ratio, which is the definition of a compound.
A compound must contain atoms of more than one element joined by chemical bonds. Each water molecule has two hydrogen atoms bonded to one oxygen atom (a fixed 2:1 ratio). Because two different elements are involved and they are chemically combined, water is a compound, not an element.