Question

Write down the values of M (atomic number or atomic weight) and Z (atomic number) for :

(1) the element X formed from thorium-232 after six a and four B emissions?
(2) the element Y formed from uranium-238 after six a and two B emissions.

(Z=90 for thorium ; Z=92 for uranium)

Answer 1

(1) Z = 82, M = 208; (2) Z = 82, M = 208

Explanation:

(1) Decay of Th-232

The unbalanced nuclear equation is

`_(90)^(232)\text{Th} \longrightarrow _(x)^(y)\text{Z} +6 _(2)^(4)\text{He} + 4 _(-1)^(0)\text{e}`

The main point to remember in balancing nuclear equations is that the sums of the superscripts and the subscripts must be the same on each side of the equation.

Then

90 = x + 6×2 + 4(-1), so x = 90 – 12 + 4 = 82

232 = y + 6×4 + 4×0, so y = 232 – 24 = 208

Z = 82, M = 208

(2) Decay of U-238

The unbalanced nuclear equation is

`_(92)^(238)\text{U} \longrightarrow _(x)^(y)\text{Z} +6 _(2)^(4)\text{He} + 2 _(-1)^(0)\text{e}`

Then

92 = x + 6×2 + 2(-1), so x = 92 – 12 + 2 = 82

238 = y + 6×4 +4×0, so y = 238 – 24 = 214

Z = 82, M = 214