Balancing Nuclear Equations: Mass & Atomic Number Confusion

[ayans2495]

Homework Statement

A particle is missing from the right-hand side of a nuclear equation. The atomic numbers on the left-hand side of a nuclear equation add to 20. The sum of the atomic numbers on the right-hand side of the equation add to 18. What is the atomic number of the missing particle?

Relevant Equations

That is the question.

I don't understand, in balancing a nuclear equation, the sum of all the mass numbers and atomic numbers, given on the upper left and lower left side of the element symbol, respectively, must be equal for both sides of the equation. So why does the sum on the left side equal to 20, but the sum on the right is equal to 18?

 

[hmmm27]

The equation given is incomplete : you're supposed to find out what's missing.

 

[ayans2495]

I suppose it's an alpha particle (helium nucleus). Though it was the wording of the question that confused me. It's an equation, the sum on one side must equal the sum on the other side. Or perhaps I just read incorrectly. Thank you for your help.