Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Solving Problems: A Chemistry Handbook
Chemistry: Matter and Change
59
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 6
Ionization energy Energy is required to pull an electron away
from an atom. The first ionization energy of an element is the
amount of energy required to pull the first valence electron away
from an atom of the element. Atoms with high ionization energies,
such as fluorine, oxygen, and chlorine, are found on the right side of
the periodic table and are unlikely to form positive ions by losing
electrons. Instead, they usually gain electrons, forming negative
ions.
Atoms with low ionization energies, such as sodium, potassium,
and strontium, lose electrons easily to form positive ions and are on
the left side of the periodic table. Recall that atoms decrease in size
from left to right across a period. First ionization energies generally
increase across a period of elements primarily because the electrons
to be removed are successively closer to the nucleus. First ionization
energies decrease moving down through a group of elements
because the sizes of the atoms increase and the electrons to be
removed are farther from the nucleus.
Practice Problems
17. For each of the following pairs, predict which atom has the
higher first ionization energy.
a. Mg, Na
d. Cl, I
b. S, O
e. Na, Al
c. Ca, Ba
f. Se, Br
18. For each of the following pairs, predict which atom forms a
positive ion more easily.
a. Be, Ca
d. K, Ca
b. F, I
e. Sr, Sb
c. Na, Si
f. N, As
The octet rule When atoms lose or gain electrons, they generally
do so until the ion has eight valence electrons—the stable s 2 p 6
electron configuration of a noble gas. This principle is called the
octet rule. Exceptions to this rule are hydrogen, which can gain an
electron, obtaining the stable 1s 2 configuration of helium, and
elements in period 2, such as lithium and beryllium, that lose
electrons, also obtaining the helium configuration.
▲
▲
Solving Problems: A Chemistry Handbook
Chemistry: Matter and Change
59
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 6
Ionization energy Energy is required to pull an electron away
from an atom. The first ionization energy of an element is the
amount of energy required to pull the first valence electron away
from an atom of the element. Atoms with high ionization energies,
such as fluorine, oxygen, and chlorine, are found on the right side of
the periodic table and are unlikely to form positive ions by losing
electrons. Instead, they usually gain electrons, forming negative
ions.
Atoms with low ionization energies, such as sodium, potassium,
and strontium, lose electrons easily to form positive ions and are on
the left side of the periodic table. Recall that atoms decrease in size
from left to right across a period. First ionization energies generally
increase across a period of elements primarily because the electrons
to be removed are successively closer to the nucleus. First ionization
energies decrease moving down through a group of elements
because the sizes of the atoms increase and the electrons to be
removed are farther from the nucleus.
Practice Problems
17. For each of the following pairs, predict which atom has the
higher first ionization energy.
a. Mg, Na
d. Cl, I
b. S, O
e. Na, Al
c. Ca, Ba
f. Se, Br
18. For each of the following pairs, predict which atom forms a
positive ion more easily.
a. Be, Ca
d. K, Ca
b. F, I
e. Sr, Sb
c. Na, Si
f. N, As
The octet rule When atoms lose or gain electrons, they generally
do so until the ion has eight valence electrons—the stable s 2 p 6
electron configuration of a noble gas. This principle is called the
octet rule. Exceptions to this rule are hydrogen, which can gain an
electron, obtaining the stable 1s 2 configuration of helium, and
elements in period 2, such as lithium and beryllium, that lose
electrons, also obtaining the helium configuration.
▲
▲