Download Concepts

All of the following answers are straight from the book. Let me know if there’s a
question about any of these answers. Problem #7 is NOT on the test.
Concepts
Section 12.1
2. The atomic number tells you the number of protons in the atom and therefore the
identity of the atom. The mass number is the sum of the number of protons plus the
number of neutrons for the atom.
Section 12.2
4. The electron is the particle that is most responsible for its chemical properties.
Electrons are involved in chemical bonding, so they determine how an atom combines
with other atoms to form compounds.
5. The specific colors of the spectral lines correspond to differences in energy between
energy levels. The fact that the spectrum is not continuous is further evidence that
electrons cannot be between energy levels.
6. Bohr explained that specific colors of spectral lines are the result of electrons that are
transitioning from higher energy levels to lower energy levels. The difference in these
energy levels is emitted as a light. The specific color corresponds to the particular
energy level from which the electron originates and the energy level to which the
electron falls.
7. An electron in the ground state is in the lowest possible energy level. An excited
electron is in a higher energy level and unstable. Electrons in excited states will
eventually fall back down to the ground state.
8. When an electron falls from a higher to a lower energy level, energy is released in the
form of light of a specific color called a photon.
Section 12.3
11. A period includes all elements on a horizontal row on the periodic table. The
properties of the elements gradually change across the period. A group includes the
elements in a vertical column on the periodic table. All group members share similar
properties.
12. The mass number of an element is the sum of the number of protons and neutrons
for one particular isotope of an element. The atomic mass is the weighted average mass
in amu’s of all known isotopes of an element.
13. The period number and the energy level of the outermost electrons in an atom are
the same.
Section 12.4
14. Possible answers include: melting point, boiling point, and the energy required to
remove an electron from an atom (ionization).
Problems
Section 12.1
1. Atom A = chlorine; atomic no. 17; mass no. 35
Atom B = calcium; atomic no. 20; mass no. 40
Atom C = copper; atomic no. 29; mass no. 63
Atom D = bromine; atomic no. 35; mass no. 80
2. Answers: a. 15 b. 7 c. 7
Section 12.2
3. Atom D
4. Diagram illustrating the filled energy levels for a carbon atom:
Section 12.3
5. a. M b. N c. N d. M e. T
Section 12.4
6. Answers are:
a. Bromine and mercury are liquids at room temperature.
b. Any five of the following are gases at room temperature: hydrogen, nitrogen, oxygen,
fluorine, chlorine, helium, neon, argon, krypton, xenon, and radon.
7. Answers are:
a. nitrogen 77%, oxygen 21%
b. oxygen 46%
Applying Your Knowledge
2. Answer: The red lines are to the left in the graphic and the blue/violet are to the
right. The shortest wavelength corresponds to the highest energy. Violet lines have the
highest energy and red have the lowest energy.
4. Elements with symbols that don’t match their names: sodium, tungsten, iron, gold,
silver, mercury, tin, lead, and antimony. Au (gold) comes from Latin word “aurum,”
which means gold. Ag (silver) comes from Latin word “argentum,” which means silver.
W (tungsten) comes from the German word “wolfram,” which means tungsten.
5. The periodic table is arranged according to atomic number. An element’s atomic
number indicates how many protons it has. Given that the number of electrons for an
atom equals the number of protons, arranging atoms by atomic number means that
they are also arranged according to their ability to bond with other atoms (their
chemical properties). Arranging the table by mass creates discrepancies within the
pattern of the elements. The periodicity of the elements is not entirely lost if the
elements are arranged by atomic mass. Since the periodic table developed before
subatomic particles were discovered, the original tables were based on atomic mass
because scientists at the time were able to see trends in how atoms behaved if you
arranged them by atomic mass. However, the periodic table is a much more useful tool
for working with the elements and getting information about them quickly, if it is
arranged by atomic number.