Final answer:
Four phosphorus atoms combine to form a single molecule of elemental phosphorus, corresponding to the P4 molecule found in white phosphorus, when comparing the mass of a single molecule with the atomic mass of phosphorus.
Step-by-step explanation:
The mass of a single molecule of elemental phosphorus provided is 2.057 × 10⁻²² g. To determine how many atoms combine to form a single molecule of elemental phosphorus, we need to compare this mass with the atomic mass of a phosphorus atom.
The atomic mass of phosphorus (P) is approximately 30.97 g/mol. Since one mole of atoms contains Avogadro's number of atoms (6.02 × 10²³ atoms/mol), we can calculate the mass of a single P atom:
30.97 g/mol ÷ (6.02 × 10²³ atoms/mol) = 5.145 × 10⁻²³ g/atom.
Elemental phosphorus exists in different forms, known as allotropes, with one of the most common being white phosphorus, which consists of P4 molecules. Thus, to find the number of atoms in a molecule with the given mass, we divide the mass of a single molecule by the mass of a single atom:
2.057 × 10⁻²² g ÷ 5.145 × 10⁻²³ g/atom = 4 atoms.
This calculation indicates that four phosphorus atoms combine to form a single molecule of elemental phosphorus, corresponding to the P4 molecule found in white phosphorus.