Chemistry CPE: A, E, M, C, Quiz - Lee

Atom

The smallest unit of matter that still has the properties of an element; a single particle that may or may not be bonded.

Element

A pure substance made of only one type of atom; can be a single atom or bonded atoms of the same type (e.g., O₂).

Molecule

Two or more atoms bonded together; can be the same type (O₂) or different types (H₂O).

Compound

A pure substance made of two or more different elements chemically combined in fixed ratios (e.g., H₂O, CO₂).

Every compound is a molecule

True; but not every molecule is a compound.

Atom classification rule

If it’s just one particle not bonded, it’s an atom.

Element classification rule

If all atoms are the same type (bonded or not), it’s an element.

Molecule classification rule

If two or more atoms are bonded, it’s a molecule.

Compound classification rule

If two or more different atoms are bonded, it’s a compound.

Example: He (one helium)

1 atom, 1 element, not a molecule or compound.

Example: O₂

2 atoms, 1 element, 1 molecule, 0 compounds.

Example: H₂O

3 atoms, 2 elements, 1 molecule, 1 compound.

Example: Na + Cl₂ (separate)

3 atoms, 2 elements, 1 molecule, 0 compounds.

Example: NaCl

2 atoms, 2 elements, 1 molecule, 1 compound.