Question

(c) calculate the mass of the 2 electrons gained by oxide anion in atomic mass units.
(d) does the mass of a oxygen atom change significantly when it gains electrons to become an anion?

Explanation:

Step1: Recall electron mass in amu

The mass of a single electron is approximately $5.48579909070\times 10^{-4}$ atomic - mass units (amu).

Step2: Calculate mass of 2 electrons

We multiply the mass of one electron by 2. So, $m = 2\times5.48579909070\times 10^{-4}\text{ amu}\approx1.09716\times 10^{-3}\text{ amu}$.

Step3: Analyze oxygen - atom mass change

The mass of an oxygen atom is mainly concentrated in its nucleus (protons and neutrons). The mass of an electron is extremely small compared to the mass of a proton or a neutron. When an oxygen atom gains electrons to become an anion, the increase in mass due to the electrons is negligible. For example, the mass of an oxygen - 16 atom is about 16 amu, and adding a few electrons (with a mass of around $10^{-3}$ amu each) does not cause a significant change.

Answer:

c) $1.09716\times 10^{-3}$
d) No, the mass of an oxygen atom does not change significantly when it gains electrons to become an anion because the mass of electrons is extremely small compared to the mass of the nucleus.