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nadezda [96]
3 years ago
6

How many neutrons does element X have if its atomic number is 21 and its mass number is 95?

Chemistry
1 answer:
Softa [21]3 years ago
3 0
Atomic # = #of Protons(21)
Mass #= #of neutrons and protons(95)
Neutrons=74

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Explanation:

In a Face-centered cubic unit cell you have 4 atoms. Also, the edge length is √8×r (r is radius of the atom).

To solve this problem, we need first to calculate the volume of the unit cell and then, with molar mass calculate the mass of 4 atoms. As density is the ratio between mass and volume we can obtain this value.

  • <em>Volume of the unit cell</em>

Volume = a³

a = √8×r

(r = 198x10⁻¹²m)

a = 5.6x10⁻¹⁰ m

Volume = 1.756x10⁻²⁸ m³

1m = 100cm → 1m³ = (100cm)³:

1.756x10⁻²⁸ m³× ((100cm)³ / 1m³) =

<h3> 1.756x10⁻²² cm³ → Volume of the unit cell in cm³</h3><h3 />
  • <em>Mass of the unit cell:</em>

<em>There are 4 atoms of gold:</em>

4 atoms × (1mol / 6.022x10²³ atoms) = 6.64x10⁻²⁴ moles of gold

As 1 mole weighs 195.08g:

6.64x10⁻²⁴ moles of gold × (195.08g / mol) =

<h3>1.296x10⁻²¹g is the mass of the unit cell</h3><h3 />
  • <em>Density of the metal:</em>

1.296x10⁻²¹g / 1.756x10⁻²² cm³ =

<h3>7.38 g/cm³ is the density of the metal</h3>
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