General orrganic and biological chemistry structures off liffe 5th by karen timberlake04 worked examples

Sample Problem 4.1 Names and Symbols of Chemical Elements
Complete the following table with the correct symbol or name of each element:

Solution

Study Check 4.1
Write the chemical symbols for the elements silicon, sulfur, and silver.

Answer
Si, S, and Ag

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Sample Problem 4.2 Metals, Nonmetals, and Metalloids
Use the periodic table to classify each of the following elements by its group and period, group name (if any),
and as a metal, a nonmetal, or a metalloid:
a. Na, important in nerve impulses, regulates blood pressure
b. I, needed to produce thyroid hormones
c. Si, needed for tendons and ligaments

Solution
a. Na (sodium), Group 1A (1), Period 3, is an alkali metal.
b. I (iodine), Group 7A (17), Period 5, halogen, is a nonmetal.
c. Si (silicon), Group 4A (14), Period 3, is a metalloid.

Study Check 4.2
Strontium is an element that gives a brilliant red color to fireworks.

a. In what group is strontium found?
b. What is the name of this chemical family?
c. In what period is strontium found?
d. Is strontium a metal, a nonmetal, or a metalloid?

Answer
a. Group 2A (2)

b.

alkaline earth metals

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

c.

Period 5

d.

metal

© 2016 Pearson Education, Inc.


Sample Problem 4.3 Subatomic Particles
Indicate whether each of the following is true or false:
a. A proton is heavier than an electron.
b. An electron is attracted to a neutron.

c. The nucleus contains all the protons and neutrons of an atom.

Solution
a. True
b. False; an electron is attracted to a proton.
c. True

Study Check 4.3
Is the following statement true or false?
The nucleus occupies a large volume in an atom.

Answer
False, most of the volume of the atom is outside the nucleus.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Sample Problem 4.4 Calculating Numbers of Protons, Neutrons,
and Electrons
Zinc, a micromineral, is needed for metabolic reactions in cells, DNA synthesis, the growth of bones, teeth, and
connective tissue, and the proper functioning of the immune system. For an atom of zinc that has a mass number
of 68, determine the following:
a. the number of protons
b. the number of neutrons
c. the number of electrons

Solution

a. Zinc (Zn), with an atomic number of 30, has 30 protons.
b. The number of neutrons in this atom is found by subtracting number of protons (atomic number) from the
mass number.

c. Because the zinc atom is neutral, the number of electrons is equal to the number of protons. A zinc atom has
30 electrons.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Sample Problem 4.4 Calculating Numbers of Protons, Neutrons,
and Electrons
Continued

Study Check 4.4
How many neutrons are in the nucleus of a bromine atom that has a mass number of 80?

Answer
45

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.

Sample Problem 4.5 Identifying Protons and Neutrons in Isotopes
Chromium, a micromineral needed for maintenance of blood sugar levels, has four naturally occurring isotopes:
a.

b.

c.

d.

Determine the number of protons and number of neutrons in each of these isotopes.

Solution

In the atomic symbol, the mass number is shown in the upper left corner of the symbol, and the atomic number is
shown in the lower left corner of the symbol. Thus, each isotope of Cr, atomic number 24, has 24 protons. The
number of neutrons is found by subtracting the number of protons (24) from the mass number of each isotope.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Sample Problem 4.5 Identifying Protons and Neutrons in Isotopes
Continued

Study Check 4.5
Vanadium is a micromineral needed in the formation of bones and teeth. Write the atomic symbol for the single
naturally occurring isotope of vanadium, which has 27 neutrons.

Answer

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Sample Problem 4.6 Calculating Atomic Mass
Magnesium is a macromineral needed in the
contraction of muscles and metabolic reactions.
Using Table 4.7, calculate the atomic mass for
magnesium using the weighted average mass
method.

Solution
Step 1

Multiply the mass of each isotope by its percent abundance divided by 100.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Sample Problem 4.6 Calculating Atomic Mass
Continued
Step 2

Add the contribution of each isotope to obtain the atomic mass. Add the contribution of each isotope to
give the weighted average mass, which is the atomic mass.
Atomic mass of Mg = 18.88 amu + 2.531 amu + 2.902 amu
= 24.31 amu (weighted average mass)

Study Check 4.6
There are two naturally occurring isotopes of boron. The isotope 105 B has a mass of 10.01 amu with an
abundance of 19.80%, and the isotope 115 B has a mass of 11.01 amu with an abundance of 80.20%.
Calculate the atomic mass for boron using the weighted average mass method.

Answer
10.81 amu

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Sample Problem 4.7 Drawing Orbital Diagrams
Nitrogen is an element that is used in the formation of amino acids, proteins, and nucleic acids. Draw the orbital
diagram for nitrogen.

Solution
Step 1

Draw boxes to represent the occupied orbitals. Nitrogen has atomic number 7, which means it has seven
electrons. For the orbital diagram, we draw boxes to represent the 1s, 2s, and 2p orbitals.

Step 2

Place a pair of electrons with opposite spins in each filled orbital. First, we place a pair of electrons with
opposite spins in both the 1s and 2s orbitals.

Step 3

Place the remaining electrons in the last occupied sublevel in separate orbitals. Then we place the three
remaining electrons in three separate 2p orbitals with arrows drawn in the same direction.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Sample Problem 4.7 Drawing Orbital Diagrams
Continued

Study Check 4.7
Draw the orbital diagram for fluorine.
Answer

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Sample Problem 4.8 Orbital Diagrams and Electron Configurations

Silicon is a micromineral needed for the growth of bones, tendons, and ligaments. Draw or write each of the
following for silicon:
a. orbital diagram
b. abbreviated orbital diagram
c. electron configuration
d. abbreviated electron configuration

Solution

a. Place two electrons in each orbital, and single electrons in the highest energy level.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Sample Problem 4.8 Orbital Diagrams and Electron Configurations
Continued
b. Write the symbol for the preceding noble gas followed by the orbitals for the remaining electrons.

c. List the sublevels in order of filling and add the number of electrons.
1s22s22p63s23p2

Electron configuration for Si

d. Write the symbol for the preceding noble gas followed by the configuration for the remaining electrons.
[Ne]3s23p2

Abbreviated electron configuration for Si

Study Check 4.8
Write the complete and abbreviated electron configurations for sulfur, which is a macromineral in proteins,
vitamin B1, and insulin.

Answer
1s22s22p63s23p4, [Ne]3s23p4

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Sample Problem 4.9 Using Sublevel Blocks to Write Electron
Configurations
Chlorine is a macromineral that is prevalent in extracellular fluids and stomach acid. Use the sublevel blocks on
the periodic table to write the electron configuration for chlorine.

Solution
Step 1

Locate the element on the periodic table. Chlorine (atomic number 17) is in Group 7A (17) and Period 3.

Step 2

Write the filled sublevels in order, going across each period.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Sample Problem 4.9 Using Sublevel Blocks to Write Electron
Configurations
Continued
Step 3

Complete the configuration by counting the electrons in the last occupied sublevel block. Because
chlorine is the fifth element in the 3p block, there are five electrons in the 3p sublevel.

The electron configuration for chlorine (Cl) is: 1s22s22p63s23p5.

Study Check 4.9
Use the sublevel blocks on the periodic table to write the electron configuration for magnesium, a macromineral needed
to form bones and required for metabolic reactions.

Answer
1s22s22p63s2

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Sample Problem 4.10 Using Sublevel Blocks to Write Electron
Configurations
Selenium is a micromineral used in the immune system and cardiac health. Use the sublevel blocks on the periodic

table to write the electron configuration for selenium.

Solution
Step 1

Locate the element on the periodic table. Selenium is in Period 4 and Group 6A (16).

Step 2

Write the filled sublevels in order, going across each period.

Step 3

Complete the configuration by counting the electrons in the last occupied sublevel block. Because
selenium is the fourth element in the 4p block, there are four electrons to place in the 4p sublevel.

The electron configuration for selenium (Se) is: 1s22s22p63s23p64s23d104p4.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Sample Problem 4.10 Using Sublevel Blocks to Write Electron
Configurations
Continued

Study Check 4.10
Use the sublevel blocks on the periodic table to write the electron configuration for iodine, a micromineral needed for
thyroid function.

Answer
1s22s22p63s23p64s23d104p65s24d105p5

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Sample Problem 4.11 Using Group Numbers
Using the periodic table, write the group number, the period, and the valence electron configuration for the
following:
a. calcium
b. iodine
c. lead

Solution
The valence electrons are the outermost s and p electrons. Although there may be electrons in the d or f sublevels, they
are not valence electrons.
a. Calcium is in Group 2A (2), Period 4. It has a valence electron configuration of 4s2.
b. Iodine is in Group 7A (17), Period 5. It has a valence electron configuration of 5s25p5.
c. Lead is in Group 4A (14), Period 6. It has a valence electron configuration of 6s26p2.

Study Check 4.11
What are the group numbers, the periods, and the valence electron configurations for sulfur and strontium?

Answer
Sulfur is in Group 6A (16), Period 3, and has a 3s23p4 valence electron configuration.
Strontium is in Group 2A (2), Period 5, and has a 5s2 valence electron configuration.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Sample Problem 4.12 Drawing Lewis Symbols
Draw the Lewis symbol for each of the following:
a. bromine
b. aluminum

Solution
a. The Lewis symbol for bromine, which is in Group 7A (17), has seven valence electrons. Thus, three pairs of dots
and one single dot are drawn on the sides of the Br symbol.

b. The Lewis symbol for aluminum, which is in Group 3A (13), has three valence Electrons drawn as single dots on
the sides of the Al symbol.

Study Check 4.12
Draw the Lewis symbol for phosphorus, a macromineral needed for bones and teeth.

Answer

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Sample Problem 4.13 Size of Atoms

Identify the smaller atom in each of the following pairs:
a. N or F
b. K or Kr
c. Ca and Sr

Solution
a. The F atom has a greater positive charge on the nucleus, which pulls electrons closer, and makes the F atom smaller
than the N atom. Atomic size decreases going from left to right across a period.
b. The Kr atom has a greater positive charge on the nucleus, which pulls electrons closer, and makes the Kr atom
smaller than the K atom. Atomic size decreases going from left to right across a period.
c. The outer electrons in the Ca atom are closer to the nucleus than in the Sr atom, which makes the Ca atom smaller
than the Sr atom. Atomic size increases going down a group.

Study Check 4.13
Which atom has the largest atomic size, P, As, or Se?

Answer
As

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Sample Problem 4.14 Ionization Energy
Indicate the element in each group that has the higher ionization energy and explain your choice.
a. K or Na
b. Mg or Cl
c. F, N, or C

Solution
a. Na. In Na, an electron is removed from an energy level closer to the nucleus, which requires a higher ionization
energy for Na compared to K.
b. Cl. The increased nuclear charge of Cl increases the attraction for the valence electrons, which requires a higher
ionization energy for Cl compared to Mg.
c. F. The increased nuclear charge of F increases the attraction for the valence electrons, which requires a higher
ionization energy for F compared to C or N.

Study Check 4.14
Arrange Sn, Sr, and I in order of increasing ionization energy.

Answer
Ionization energy increases going from left to right across a period: Sr, Sn, I.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.