Chemistry Reference
In-Depth Information
EXAMPLE 13.3
Which atom in each of the following parts is largest?
(a) Be
Mg
Ca
(b)
Na
Mg
Al
(c)
F
Cl
Br
I
Solution
(a) Ca (The atoms get larger as we go down the group.)
(b) Na (The atoms get smaller as we go to the right.)
(c) I (The atoms get larger as we go down every group, not only the alkaline
earth metal group.)
Practice Problem 13.3
Which atom in each of the following parts
is largest?
(a) S
Se
Te
(b) Mg
Si
Cl
Snapshot Review
❒
The more protons in an atom or ion, all other factors being the same,
the smaller is the size of the species.
❒
The more electrons in an atom or ion, all other factors being the
same, the greater is the size of the species.
ChemSkill Builder 11.1
❒
When both the number of electrons and the number of protons vary,
the size varies periodically.
A. Explain why a larger number of protons produces a smaller species, all
other factors being equal.
13.2
Ionization Energy and Electron Affinity
Both ionization energy and electron affinity are measures of energies involving
gaseous atoms and gaseous ions and are not the same as the energies involved
when ionic solids or solutions are formed. The latter energies involve ioniza-
tion energy and electron affinity, but also include many other types of energy
terms.
Ionization Energy
The
ionization energy
of an element is defined as the energy
required
to remove
an electron from a
gaseous
atom to produce a
gaseous
cation. For example,
Na(g)
--------------------
¡
Ionization energy
Na
(g)
e
Gaseous atoms and ions are specified because they are far from any other chem-
ical species (Section 12.10), and thus few extraneous interactions interfere with
the nucleus-electron attraction. Note that this is
not
the energy for the more famil-
iar reaction of solid sodium to produce sodium ions in a lattice or in solution.
