1. Mass of proton : 1.6726 x 10-27 kg, or 1.0073 u
QUESTION:
Which of the following has the largest total mass? A. 2 protons + 4 electrons B. 2 neutrons + 2 protons C. 7 electrons D. they all have the same mass
Mass of proton : x kg, or u
Mass of neutron: x kg, or u
Mass of electron: x10-27 kg, or u
A proton’s mass is about 2000x that of an electron. (1836x to be more precise)
ESTIMATES: proton or neutron = 1.0 u, electron = 0 u
SCRIPT:
Which of the following has the largest total mass? A. 2 protons + 4 electrons B. 2 neutrons + 2 protons C. 6 electrons D. they all have the same mass
PAUSE
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The mass of a proton is known to be x10-27 kilograms, or atomic mass units
The mass of a neutron is almost the same… it’s x10-27 kilograms, or atomic mass units.
An electron, on the other hand, has a mass that is about 2000 time less than that of a proton or neutron.
To be more precise, a protons mass is 1836 times larger than an electron.
We don’t need to be very precise to answer this question. Let’s estimate the masses for the choices given.
To the nearest tenth of an atomic unit, the mass of proton or neutron is 1.0 and the mass of an electron is zero.
In other words, we can just ignore the electrons.
CROSS OUT 4 electrons in choices A and 6 electrons in choice C
For choice A, we ignore the mass of the electron. The mass is approximately equal to the mass of two protons; that’s 2 atomic mass units.
CALLOUT “2.0 amu”
For choice B, the approximate mass is 4 atomic mass units. Each proton and neutron has a mass of 1.0 amu, and we have four of these all together.
CALLOUT “4.0 amu”
Therefore, the correct answer is B.
PAUSE CLICK END RECORDING

2. Video ID: © 2008, Project VALUE (Video Assessment Library for Undergraduate Education), Department of Physical Sciences Nicholls State University Author: Glenn V. Lo Narrator: Funded by Louisiana Board of Regents Contract No. LA-DL-SELECT-13-07/08