Read Whether a Formula Contains One Element or More - Practice 1

An element contains one kind of atom, even when its atoms occur in molecules.

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An element contains one kind of atom, even when its atoms occur in molecules. A compound contains different elements chemically combined. Count distinct element symbols, not total atoms. These are formula-reading questions.

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O2 contains only oxygen and is an elemental substance. CO2 contains carbon and oxygen and is a compound.

O2 is shown as two oxygen atoms and CO2 as one carbon with two oxygens. O2 has one kind of element; CO2 has two. Bonds and sizes are schematic.

Would you believe it?

An oxygen molecule, O2, contains two atoms but only one kind of element. Counting atoms and counting elements answer different questions.

Question 1 Classify the pure substance represented by O2. elemental substance compound no atoms

Question 2 Classify the pure substance represented by H2O. elemental substance no atoms compound

Question 3 Classify the pure substance represented by N2. no atoms elemental substance compound

Question 4 Classify the pure substance represented by CO2. compound elemental substance no atoms

Question 5 Classify the pure substance represented by He. compound no atoms elemental substance

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