1.

​ The table below gives the atomic mass and the abundance of the 2 naturally
occurring isotopes of chlorine.

Which numerical setup can be used to calculate the atomic mass of the element
chlorine?
Answer: (34.97u)(.7576) + (36.97u)(.2424)
Explanation: The chart shows percent abundance. The masses must be multiplied by the
% abundance divided by 100. That moves the decimal 2 places to the left. The correct
setup is above.

1.​ If 75.0% of the isotopes of an element have a mass of 35.0 amu and 25.0% of the
isotopes have a mass of 37.0amu, what's the atomic mass of the element?
Answer: 35.5 amu
Explanation: The atomic mass of an element is a weighted average, in accordance
to the proportions in which the isotopes occur. For the element in question, the
atomic mass is calculated as: (0.75 x 35.0) + (.25 x 37.0) = 35.5 amu

1.​ What is the number of valence electrons in a nitrogen atom in the ground state?
Answer: 5
Explanation: A nitrogen atom in the ground state has a total of 5 valence electrons.
Nitrogen has a ground state electron configuration of 2-5. Valence electrons are
those electrons found in the outermost energy levels of the atom.

1.​ Base your answer to the question on the info. Naturally occurring elemental
carbon is a mixture of isotopes. The % composition of the 2 most abundant
isotopes is listed below. 98.93% of the carbon atoms have a mass of 12.00 atomic
mass units. 1.07% of the carbon atoms have a mass of 13.00 atomic mass units.
Which of the following is a correct numerical setup for calculating the average
atomic mass of carbon?
Answer:

Explanation: Multiply each mass by the percentage of that mass that exists in
nature. Then add the 2 together and divide by 100.

1.​ An orbital is a region in an atom where there is a high probability of finding

Answer: an electron
 Explanation: An orbital Is a region an atom where there is high probability of finding
an electron. The energy of an orbital increases the further away from the nucleus it
is located. Therefore, an electron in an orbital in the first energy level has less
energy than an electron in an orbital in the second or third.

1.​ 2 atoms that are different isotopes of the same element have
Answer: the same number of protons but a different number of neutrons
Explanation: 2 atoms that are different isotopes of the same element have the same
number of protons but different number of neutrons resulting in different masses.

1.​ Carbon has 3 naturally occurring isotopes, C-12, C-13, and C-14. Diamond and
graphite are familiar forms of solid carbon. Diamond is one of the hardest
substances known, while graphite is a very soft substance. Diamond has a rigid
network of bonded atoms. Graphite has atoms bonded in thin layers that are held
together by weak forces. Recent experiments have produced new forms of solid
carbon called fullerenes. One fullerene, C60, is a spherical, cage like molecule of
carbon. Determine both the total number of protons and the total number of
neutrons in an atom of the naturally occurring carbon isotope w/the largest mass
number.
Answer: protons: 6 neutrons: 8
Explanation: All the isotopes of carbon have 6 protons. C-14 will also have 8
neutrons to bring the mass to 14.

1.​ Which Lewis electron-dot diagram represents a nitrogen atom in the ground
state?
Answer:

Explanation: Electron dot diagrams only show the valence electrons. The Periodic
table of the elements shows that the ground state electron configuration of nitrogen
is 2-5. This means that nitrogen has 5 valence electrons.

1.​ As a result of the gold foil experiment, it was concluded that an atom
Answer: contains a small, dense nucleus
Explanation: Alpha particles shot at the gold foil bounced back. The conclusion was
that an atom has a small dense nucleus.

1.​ The discovery of the electron as a subatomic particle was a result of

Answer: experiments w/cathode ray tubes
Explanation: The discovery of the electron as a subatomic particle was a result of
experiments w/cathode ray tubes by JJ Thomson. He applied charged metal plates
to the outside of the cathode ray tube and observed the behavor of the cathode ray
bend towards the positive plate indicating they were negatively charged.
1.​ According to the wave-mechanical model, an orbital is defined as the
Answer: most probable location of electrons
Explanation: An orbital is the most likely place to find an electron

1.​ An ion that consists of 7 protons, 9 neutrons, and 10 electrons has a net charge of
Answer: 3-
Explanation: Protons are positively charged, neutrons are neutral, and electrons are
negatively charged. 7+ protons and 10-electrons results in a 3- charged ion.

1.​ What's the total number of neutrons in an atom of K-42?

Answer: 23
Explanation: The mass # of an atom is the total # of protons and neutrons. K-42 has
a mass # of 42. Potassium has an atomic # of 19 which indicates the # of protons in
each of the element's atoms. Therefore, the remaining 23 from the mass # is from
the neutrons. Mass # = # protons + # neutrons. 42 = 19 + # neutrons. 42-19= #
neutrons. 23=# neutrons.

1.​ Which conclusion directly resulted from the "gold foil experiment"?
Answer: Atoms are mostly empty space.
Explanation: In Rutherford's famous gold foil experiment, most of the alpha
particles went straight through the foil unaffected. Therefore, he concluded that
atoms are mostly empty space.

1.​ The numbers of protons and neutrons in each of 4 different atoms are shown in
the table below.

Which 2 atoms represent isotopes of the same element?

Answer: D and E
Explanation: Isotopes of the same element will have the same # of protons but
different #'s of neutrons. Therefore, D and E are isotopes of the same element b/c
they both have 9 protons.
1.​ Base your answer to the question on your knowledge of chemistry and the
bright-line spectra produced by 4 elements and the spectrum of a mixture of
elements represented in the diagram below.

Each line in the spectra represents the energy

Answer: released as an electron moves from a higher energy state to a lower energy
state
Explanation: Each element has its' own unique bright-line spectra that is produced
when excited electrons return to their ground state. As electrons move from a
higher to a lower energy state they emit energy in the form of specific wavelengths
of light represented by each line in the spectra.

1.​ Which quantity represents the number of protons in an atom?

Answer: atomic number
Explanation: The atomic # is the # of protons in the atom

1.​ Which electron configuration represents the electrons of a phosphorus atom in an

excited state?
Answer: 2-7-6
Explanation: The ground state electron configuration is when all electrons are in the
lowest possible configuration for each energy level. When an atom absorbs excess
energy, electrons move to higher energy levels, which result in an excited state.
This results in electrons in a higher energy level than they were in the ground state,
which can be seen in the electron configuration 2-7-6 since the 2nd energy level can
normally hold 8 electrons.
1.​ The bright-line spectrum of an element is produced when excited-state electrons
Answer: release energy and move to lower energy states
Explanation: When an electron absorbs energy, it moves to a higher energy level.
The bright-line spectrum of an element is produced when excited-state electrons
release the added energy the absorbed and move back down to lower energy states.

1.​ The diagram below represents the bright-line spectra of 4 elements and a
bright-line spectrum produced by an unidentified element.

What is the unidentified element?

Answer: L
Explanation: According to the given diagram representing the bright-line spectra of
4 elements, it can be seen that the unidentified element is Element L. When an
excited electron falls back down to a lower energy level it emits a photon w/an
energy equal to the difference in energy levels producing a bright-line spectra
unique to each element.

1.​ What's the net charge of an ion that has 11 protons, 10 electrons, and 12
neutrons?
Answer: 1+
Explanation: The net charge of an ion that has 11 protons, 10 electrons, and 12
neutrons is +1. This is found by calculating the sum of the positive charges from the
# of protons and the negative charges from the electrons. Since there is 1 more
positive charge than negative, there is a net charge of +1.

1.​ Base your answer to this question on the info below.

 What's the correct Lewis electron-dot diagram for an atom of sulfur-33
Answer:

Explanation: An atom of sulfur has 6 valence electrons. Those 6 electrons are used
in the Lewis electron-dot diagram for an atom of sulfur-33.

1.​ Given the bright-line spectra of 3 elements and the spectrum of a mixture formed
from at least 2 of these elements:

Which elements are present in this mixture?

Answer: E and D, only
Explanation: The bright line spectra of elements E and D line up w/the bright line
spectrum of the mixture as seen in the diagram. Element D is highlighted in red and
element E is highlighted in green.
1.​ What's the charge of the nucleus of a copper atom?
Answer: +29
Explanation: The nucleus of an atom contains protons and neutrons. The protons
have a +1 charge and the neutrons have no charge. Each copper atom has 29
protons, so it has a +29 charge.

1.​ Which conclusion was a direct result of the gold foil experiment?
Answer: An atom is mostly empty space w/a dense, positively charged nucleus
Explanation: Alpha particles bombarded the thin gold sheets in the gold foil
experiment. Most of the particles passed through, but some were deflected. This
caused Rutherford to theorize that an atom is mostly empty space w/a dense,
positively charged nucleus.