Structure Of The Atom Worksheet With Answer Key Page 8
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22ChemQuest 10
Name: ____________________________
Date: _______________
Hour: _____
Information: Bohr’s Solar System Model of the Atom
All the planets are attracted to the sun by gravity. The reason that the Earth doesn’t just float out
into space is because it is constantly attracted to the sun. Similarly, the moon is attracted to the
Earth by Earth’s gravitational pull. So all of the planets are attracted to the sun but they never
collide with the sun.
Negative charges are attracted to positive ones. Therefore the negative electrons in an atom are
attracted to the positive protons in the nucleus. In the early 1900’s scientists were looking for an
explanation to a curious problem with their model of the atom. Why don’t atoms collapse? The
negative electrons should collapse into the nucleus due to the attraction between protons and
electrons. Why doesn’t this happen? Scientists were at a loss to explain this until Neils Bohr
proposed his “solar system” model of the atom.
Critical Thinking Questions: Bohr’s reasoning
1. Consider swinging a rock on the end of a string in large circles. Even though you are
constantly pulling on the string, the rock never collides with your hand. Why is this?
The rock must move so quickly that the pull from your hand is not enough to pull the rock
into your hand. If you were to let go, it would fly away from you in a straight line. The pull
from your hand keeps the rock near you, but because of its initial velocity it doesn’t get
closer to you.
2. Even though the Earth is attracted to the sun by a very strong gravitational pull, what keeps
the Earth from striking the sun?
The fact that the earth is moving keeps it from striking the sun. The earth would move away
from the sun, but the gravity of the sun attracts it, causing a circular orbit for the earth.
3. Why doesn’t the moon strike the Earth?
The reasoning is the same as that for questions 1 and 2.
4. How could it be possible for electrons to not “collapse” into the nucleus?
The electrons must be moving in orbits so fast that the pull from the nucleus is not enough to
attract them toward the nucleus—this is Bohr’s “solar system model” of the atom.
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