Which
of these metals has the most negative electron affinity?
A. B. C. D. E. calcium cadmium chromium copper cobalt
[Ar]4s2 [Kr]5s24d10 [Ar]4s13d5 [Ar]4s13d10 [Ar]4s23d7
Atomic radius measures how strongly the outer shell valence electrons of an atom are attracted to the nucleus. The bigger the atomic radius, the further the valence electrons are from the nucleus, the less attraction they experience.
Electron Affinity measures how readily a neutral atom can gain an electron. As the electron affinity becomes more negative, the tendency to gain an electron gets bigger.
Ionization Energy measures how readily an atom or ion releases an electron. As the ionization energy gets bigger, the tendency to release an electron gets smaller.
Which of these metals has the most negative electron affinity?
A. B. C. D. E. calcium cadmium chromium copper cobalt
[Ar]4s2 [Kr]5s24d10 [Ar]4s13d5 [Ar]4s13d10 [Ar]4s23d7
Atoms can lose or gain electrons to become ions.
Atoms can lose or gain electrons to become ions.
For cations, electrons are taken away from the outermost subshell, making cations smaller than their parent atoms.
Na: [Ne]3s1 Na+: [Ne]
Mg: [Ne]3s2 Mg2+: [Ne]
Al: [Ne]3s23p1 Al3+: [Ne]
Atoms can lose or gain electrons to become ions.
For cations, electrons are taken away from the outermost subshell, making cations smaller than their parent atoms.
Na: [Ne]3s1 Na+: [Ne]
Mg: [Ne]3s2 Mg2+: [Ne]
Al: [Ne]3s23p1 Al3+: [Ne]
These ions are all isoelectronic with Ne (1s22s22p6). In general, for maingroup elements the most stable ions are the ones that are isoelectronic with a noble gas.
Atoms can lose or gain electrons to become ions.
For anions, electrons are added to the outermost subshell. The electron electron repulsion makes the anions bigger than their parent atoms.
S: [Ne]3s23p4 S2: [Ne] 3s23p6 = [Ar]
Cl: [Ne]3s23p5 Cl: [Ne] 3s23p6 = [Ar]
Atoms can lose or gain electrons to become ions.
For anions, electrons are added to the outermost subshell. The increase in electronelectron repulsion makes the anions bigger than their parent atoms.
Cl: [Ne]3s23p5 Cl: [Ne] 3s23p6 = [Ar] These ions are isoelectronic with Ar (1s22s22p63s23p6). In general, for maingroup elements the most stable ions are the ones that are isoelectronic with a noble gas.
S: [Ne]3s23p4 S2: [Ne] 3s23p6 = [Ar]
In general, metals lose electrons to become cations. gain Nonmetals electrons to become anions.
Figure 8.29
Ionic vs. atomic radius.
SAMPLE PROBLEM 8.8 PROBLEM:
Ranking Ions by Size
Rank each set of ions in order of decreasing size, and explain your ranking: (a) Ca2+, Sr2+, Mg2+ (b) K+, S2, Cl (c) Au+, Au3+
PLAN:
Compare positions in the periodic table, formation of positive and negative ions and changes in size due to gain or loss of electrons.
SOLUTION: (a) Sr2+ > Ca2+ > Mg2+ These are members of the same Group (2A/2) and therefore decrease in size going up the group. The ions are isoelectronic; S2 has the smallest Zeff and therefore is the largest while K+ is a cation with a large Zeff and is the smallest. (c) Au+ > Au3+
(b) S2 > Cl > K+
The higher the + charge, the smaller the ion.
Maingroup ions and the noble gas configurations.
Figure 2.19
Some common monatomic ions of the elements.
Can you see any patterns?
The Period 4 crossover in sublevel energies. The 4s subshell is lower in energy than the 3d subshell. Electrons fill the 4s subshell first. Once electrons are placed inside the 3d subshell, those electrons become more stable. When transition metals lose electrons to become cations, electrons are lost from the 4s subshell first. "First in, first out"
SAMPLE PROBLEM 8.6 PROBLEM:
Writing Electron Configurations of MainGroup Ions
Using condensed electron configurations, write reactions for the formation of the common ions of the following elements: (b) Potassium (Z = 19) (c) Indium (Z = 49)
(a) Iodine (Z = 53) PLAN:
Ions of elements in Groups 1A(1), 2A(2), 6A(16), and 7A(17) are usually isoelectronic with the nearest noble gas. Metals in Groups 3A(13) to 5A(15) can lose their np or ns and np electrons.
SOLUTION: (a) Iodine (Z = 53) is in Group 7A(17) and will gain one electron to be isoelectronic with Xe: I ([Kr]5s24d105p5) + e I ([Kr]5s24d105p6) K ([Ar]4s1) K+ ([Ar]) + e (c) Indium (Z = 49) is in Group 3A(13) and can lose either one electron or three electrons: In ([Kr]5s24d105p1) In+ ([Kr]5s24d10) + e+ In ([Kr]5s24d105p1) In3+([Kr] 4d10) + 3e
(b) Potassium (Z = 19) is in Group 1A(1) and will lose one electron to be isoelectronic with Ar:
Figure 8.27
Apparatus for measuring the magnetic behavior of a sample.