Online
Introductory Chemistry
Answers to atoms and periodic table self test
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Dr.
Walt Volland all right reserved, revised April 1, 2005
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1.
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What is the number
of electrons, protons and neutrons in an atom of radon-224?
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- Answer:
- There
are 86 protons in the radon nucleus. You determine this by looking
for Rn in the periodic table and reading the atomic number for Rn.
- There
are 86 electrons in a neutral radon atom because the 86 positive protons
must have 86 negative electrons to bring the total charge to zero.
- The
number of neutrons equals the mass number(224) minus the atomic number
(86)
- Number
neutrons = 224 - 86 = 138.
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2.
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- Copper has two
naturally occurring isotopes. What is the average atomic mass for
copper? Use the percent abundances and masses given here.
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Isotope---------------------------------------
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percent
abundance
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mass in
amu
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copper-63------------------------------------
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69.09%----------------------------
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62.93
amu----------------------------
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copper-65
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30.91%
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64.93
amu
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Answer:
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3.
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- Locate the following
on the outline of a periodic table.
- a. alkali metals
- Answer:
Alkali metals are the elements Li, Na, K,
Rb, Cs, Fr in Group 1A.
- b. halogens
- Answer:
Halogens
are the elements F, Cl, Br, I and At in Group 7A
- c. elements with
ns2np3 set of outer electrons
- Answer:
The
representative elements in Group 5A N, P, As, Sb, and Bi have five
outer electrons with the subshell ns2np3.
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4.
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Write the electron
configuration for an atom with 17 electrons. Mark the valence electrons.
What is the identity and group for this element?
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- Answer:
- Chlorine,
Cl, is an atom with 17 electrons. Chlorine is in Group 7A and is one
of the halogens.
- The
electron configuration for chlorine is 1s22s22p63s23p5.
The valence electrons are seven in the 3s23p5
subshells. Chlorine is an example of a p-block element. The outermost
electrons are in the "3p" subshell.
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5.
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Sketch an atom of
beryllium-9. Indicate the number of neutrons and protons in the nucleus.
Show the relative average distances out from the nucleus for the electron
subshells. Identify the valence electrons. Tell whether or not this
element is an s-block element.
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- Answer:
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- Beryllium,
Be, has atomic number 4. It has four(4 ) protons and four(4)
electrons. The Be-9 isotope has 5 neutrons,
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neutrons = mass number - atomic number; neutrons = 9 -4
= 5)
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- The
electron configuration for beryllium is 1s22s2.
The valence electrons are the two in the 2s2
subshell. The relative average distance for a shell is determined
on average by the values for "n". the higher the quantum
number "n" the greater the distance between the nucleus
and the electrons in the shell. this was illustrated in
the lectures when the 1s, 2s, 3s orbitals were discussed.
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- Beryllium
is an s-block element because the valence electrons are
in the 2s subshell.
All
s-block elements have the outermost electrons (valence electrons)
in an "s" subshell. The elements in Groups 1A and 2A of the
periodic table are s-block.
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