What is the approximate atomic mass of an electron?

What is the approximate atomic mass of an electron?

• A. 1 amu
• B. 1836 amu
• C. 0.0005486 amu
• D. 2 amu

Answer: (C)

Electrons are extremely light compared to protons and neutrons, so their mass in atomic mass units is a tiny fraction of 1 amu. In numbers, the electron mass is about 9.109 × 10^-31 kg, and 1 amu is about 1.6605 × 10^-27 kg. Dividing gives roughly 5.49 × 10^-4 amu, i.e., about 0.00055 amu. That’s why the atomic mass of an electron is commonly given as 0.0005486 amu. It’s also why an electron’s mass is about 1/1836 of a proton’s mass, making it negligible in many simple atomic calculations.

Electrons are extremely light compared to protons and neutrons, so their mass in atomic mass units is a tiny fraction of 1 amu. In numbers, the electron mass is about 9.109 × 10^-31 kg, and 1 amu is about 1.6605 × 10^-27 kg. Dividing gives roughly 5.49 × 10^-4 amu, i.e., about 0.00055 amu. That’s why the atomic mass of an electron is commonly given as 0.0005486 amu. It’s also why an electron’s mass is about 1/1836 of a proton’s mass, making it negligible in many simple atomic calculations.