an element has bcc with a cell edge of 288pm the density of the element is 7.2 gm/cm^3. how many atoms are present in 208gm of the element?

Volume of the unit cell = (288 * 10-12)3

= 2.39 * 10-23 cm3

Volume of 208 g of element can be calculated as follows:

= 28.88 cm3

Therefore number of unit cells in this volume:

= 12.03 * 1023 unit cells 

We know that each bcc unit cell contains 2 atoms, therefore the total number of atoms in 208 g:

2 * 12.03 * 1023 atoms

= 24.16 * 1023 atoms

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Volume of 1 unit cell = a3 = (288 x 10-10)cm3 = 2.39 x 10-23cm3

Volume of 208g of the element , V = mass./density = 208 / 7.2gcm-3 = 28.88cm3

No. of unit cells = total volume / volume of 1 unit cell = 28.88 / 2.39 * 10-23 = 12.08 * 1023 unit cells

Now , each bcc unit cell contains 2 atoms , hence , total no. of atoms in 208g = 2 * 12.08 * 1023 = 24.16 * 1023 atoms

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