1. Bohr assumed electrons move around the nucleus in circular orbits.
QUESTION:
For Bohr’s model, if “a” is radius of the first allowed orbit of hydrogen, what is the radius of the third allowed orbit? A. 3a, B. 6a, C. 8a, D. 9a
Bohr assumed electrons move around the nucleus in circular orbits.
Radius of nth orbit = (52.9 pm) n2
a = Radius of 1st orbit = (52.9 pm)(12) = 52.9 pm
Radius of nth orbit = a n2
Radius of 2nd orbit = a(2)2 = 4a
Radius of 3rd orbit = a (3)2 = 9a
NOTE: 1 Bohr = 52.9 pm
SCRIPT
For Bohr’s model, if “a” is radius of the first allowed orbit of hydrogen, what is the radius of the third allowed orbit? A. 3a, B. 6a, C. 8a, D. 9a
PAUSE CLICK
Bohr’s model assumes that electrons move around the nucleus in circular orbits.
CLICK
And predicted the radius of the nth orbit to … 52.9 picometers, times n squared
For the first orbit n equals 1.
HIGHLIGHT n and 1
Therefore, the radius of the first orbit is 52.9 picometers times one squared, or 52.9 picometers
Since a is 52.9 picometers, we can also say that the radius of the nth orbit is equal to a times n squared
CLICK Therefore, the radius of the second orbit is a times two squared, or 4a.
And the radius of the 3rd orbit is a times three squared, or 9a.
The correct answer is d.
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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 Funded by Louisiana Board of Regents Contract No. LA-DL-SELECT-13-07/08