Chapter 2- Atoms and Elements
Short Study Guide
Explain Millikan’s oil drop experiment and how it led to the measurement of the electron’s charge. Why
is the magnitude of the charge of the electron so important?
Millikan created a measurement machine that placed electrons in an oil drop and sprayed them with
ionizing radiation, thus giving the drops negative charges. The lower part of the plate was negative as
well, so the drops were able to slowed down from their gravity fall and even reversed (because like
charges repel each other). This experiment led to discover the process of measuring electrons because
Millikan found he could calculate the size of the electric field required to halt the freefall of the drops
and also figure out the drops’ mass (determined by their radii and density). Finally, the magnitude of
the mass is important because it determines how strongly an atom holds its electrons. If atoms held
their electrons more loosely they would most likely not be stable, but if they held their electrons too
tightly there would be less compounds or none at all, therefore, life would not be possible.
Describe Rutherford’s gold foil experiment. How did the experiment show that the plum- pudding
model of the atom was wrong?
Rutherford created an experiment that was to determine the structure of an atom. Since it was
discovered that electrons are present in an atom and that they are negatively charged. Since it was
assumed that atoms are neutral and electrons are negatively charged, there should be some positive
charged inside it that makes it neutral. Rutherford work under the discoveries and assumptions of an
atom which was plum pudding model. According to the model there were negatively charged particles
and electrons suspended or embedded in a sphere of positive charge. The experiment of plum pudding
was wrong because Rutherford worked with particles through gold foil, and he found that most of the
particles went through, some went to different directions or others deflected back towards the source
and because of this he state that this experiment was incorrect.
What defines an element?
Its atomic number, in other words the number of protons it contains in the nucleus.
State the periodic law. How did the periodic law lead to the periodic table?
The periodic law states as follows: “ When the elements are arranged in order of increasing mass,
certain sets of properties recur periodically.” Because of these recurring properties Mendeleev decided
to organize the known elements in horizontal rows by order of increasing mass (from left to right)
and arranged the rows so that elements with similar properties fall in the same vertical columns.
What are the characteristic properties of each of the following groups?
a. Noble gases: Mostly unreactive (8A)
b. Alkali Metals: All reactive metals (1A) c. Alkaline earth metals: Fairly reactive (2A)
d. Halogens: Very reactive nonmetals (7A)
Why is the mass corresponding to a mole of one element different from the mass corresponding to a
mole of another element?
The mass of one element different from the mass of another element because of the chemical
structure of each element. All elements are composed of the subatomic particles of protons, neutrons
and electrons, and also the mass corresponding to a mole varies with atoms.
An automobile gasoline tank holds 21kg of gasoline. When the gasoline burns, 84kg of oxygen is
consumed, and carbon dioxide and water are produced. What is the total combined mass of carbon
dioxide and water that is produced?
According to the Law of Conservation of Mass, the total mass of reactants equals the total
mass of the products. Then, if gasoline and oxygen have 21 kg and 84 kg making a total of 105 kg, then
the mass of carbon dioxide and water must be 105 kg.
How many electro