a compound forms hexagonal close packed structure. what is the total number of voids in 0.5mol of it? how many of these are tetrahedral voids?

Number of atoms in 1 mole of compound = 6.022 x 10^{23}

Number of atoms in 0.5 mol = 0.5 x 6.022 x 10^{23}

= 3.011 x 10^{23}

For a hexagonal closed packed structure,

Number of octahedral voids = number of atoms in the compound

Therefore, the number of octahedral voids =3.011 x 10^{23}

And

Number of tetrahedral voids = 2 x octahedral voids

= 2 x 3.011 x 10^{23}

= 6.022 x 10^{23}

The total number of voids = (6.022 + 3.011) x 10^{23}

= 9.033 x 10^{23}

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