2021 H2 Chem P1 Q1 — Atomic structure Solution

The answer is B (1 and 2 only).

Statement 1 is true. The angle of deflection is proportional to \(\frac{\text{charge}}{\text{mass}}\). An electron and a proton carry charges of the same size, but the mass of an electron is about \(\frac{1}{1840}\) of the mass of a proton, so \(\frac{|z|}{m}\) is far larger for the electron and the electron beam is deflected much more.

Statement 2 is true. The electron is negatively charged, so it is attracted towards the positive plate; the proton is positively charged, so it is attracted towards the negative plate. The two beams bend in opposite directions.

Statement 3 is false. The proton beam does move towards the negatively charged plate, but not in a straight line. The attractive force acts on the protons continuously while they move forward, so they accelerate sideways and follow a curved path.

• A is wrong: it includes statement 3, which is false.
• C is wrong: it leaves out statement 1, which is true, and includes statement 3, which is false.
• D is wrong: statement 3 is the only false statement, and it leaves out the true statements 1 and 2.