Elements vs Compounds

Atoms • bonds • fixed ratios

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Element: a pure substance containing only one kind of atom.

Compound: a pure substance containing atoms of two or more elements chemically bonded in a fixed ratio.

Mixture: two or more substances together without forming one fixed chemically bonded substance.

O₂ is an element molecule. H₂O is a compound molecule.

Mission

Inspect the sample and decide whether it is an element, compound, or mixture.

Experiment

SampleO₂

Particle groups6

Bond/decomposition energy45%

Simulation speed1×

Live classification

Elementsample class

1element types

O onlyatom ratio

6visible bonds

Oxygen contains only oxygen atoms, so it is an element even when atoms are bonded in O₂ molecules.

Oxygen atom

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Teacher tools

Reveal bond map

Interactive lecture

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Atoms build substances

Watch one atom become selected in the scanner.

Chapters

Learning objectives

Identify elements by a single atom type.
Recognize compounds by different atoms chemically bonded in fixed ratios.
Distinguish molecules of elements from compound molecules.
Explain why mixtures can be separated physically but compounds require chemical change.

Key concepts

An element contains one kind of atom. A compound contains atoms of two or more elements chemically bonded in a fixed ratio. A mixture contains substances together without all becoming one chemically bonded substance.

Atom sizes, bond lengths, motion, and reaction timing are educationally scaled. NaCl is shown as repeating ion pairs before its lattice close-up.

Suggested experiments

Compare O₂ with H₂O: both are molecules, but only one is a compound.
Break water bonds and verify that H and O atom counts remain conserved.
Compare an air-like mixture with carbon dioxide.
Increase group count and check whether classification changes.

Applications and misconceptions

Applications: chemical analysis, materials, air separation, water electrolysis, medicines, and recycling.

Misconception: A molecule is not automatically a compound. O₂ is a molecule but still an element because it contains only oxygen atoms.

Classification check

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