A 4.99 g sample of an unknown element contains 1.07 × 1023 atoms. Identify the unknown element.

To identify the unknown element, we need to find its atomic mass. We can do this by using Avogadro's number, which states that one mole of any substance contains 6.022 x 10^23 entities (atoms, in this case).

Step 1: Calculate the number of moles in the sample We know that the sample contains 1.07 x 10^23 atoms. To find the number of moles, we divide this number by Avogadro's number:

Number of moles = 1.07 x 10^23 atoms / 6.022 x 10^23 atoms/mole = 0.1778 moles

Step 2: Calculate the atomic mass We know that the sample weighs 4.99 g. To find the atomic mass, we divide this weight by the number of moles:

Atomic mass = 4.99 g / 0.1778 moles = 28.07 g/mole

Step 3: Identify the element The atomic mass we calculated is closest to that of silicon (Si), which has an atomic mass of approximately 28.09 g/mole. Therefore, the unknown element is likely silicon.