Question

If the mass of a single atom of an element 'E' is $\left(2.65\times {10}^{-23}\right)\mathrm{g}$, then find its atomic weight and identify the element.

Answer 1

Step 1: Formula to calculate the atomic weight:

The atomic weight of an element is numerically equal to the mass of $1\mathrm{mol}$ atoms.

We know from Avagadro's number,

$1\mathrm{mol}$ = $\left(6.022\times {10}^{23}\right)$ atoms,

Atomic weight = mass of $\left(6.022\times {10}^{23}\right)$ atoms.

Step 2: Calculate the atomic weight of element ‘E’:

Mass of one atom of E = $\left(2.65\times {10}^{-23}\right)\mathrm{g}$

Atomic weight of E = $\left(2.65\times {10}^{-23}\right)\mathrm{g}\times \left(6.022\times {10}^{23}\right)$ = $15.96\mathrm{g}$

Atomic mass is expressed in atomic weight unit $\left(\mathrm{u}\right)$.

Therefore, the atomic weight of element ‘E’ is $15.96\mathrm{u}$.

Step3: Identify element ‘E’:

1. From step 2, we know that the atomic weight of E is $15.96\mathrm{u}$
2. Element with atomic weight $15.96\mathrm{u}$ is oxygen .
3. Hence, element ‘E’ is oxygen $\mathbf{\left(}\mathbf{O}\mathbf{\right)}$.