Transcript Chemistry: McMurry and Fay, 5th Edition

Chapter 6
Ionic Bonds and
Some Main Group
Chemistry
Ions and Their Electron
Configurations
• Chapter 2
– Metals lose electrons to form cations
• Main group elements tend to lose the same # of
electrons as their group number to attain
nearest noble gas configuration
• Na, Ne, Na+
O, Ne, O2• K, Ar, K+
Cl, Ar, Cl• Ga, Ga3+
Sn, Sn4+
– Nonmetals when combined with metals
gain electrons to form anions
• The number gained = 8 – group #
Periodic Table and Electron
Configurations
• Build-up order given by position on periodic table; row
by row.
• Elements in same column will have the same outer
shell electron configuration.
Ions and Their Electron
Configurations
Diagonal Rule for Build-up
Rule
1s
2s
3s
4s
5s
6s
2p
3p
4p
5p
6p
3d
4d 4f
5d 5f
6d 6f
• The periodic table can also be used to determine
the electron configuration of an element.
Ions and Their Electron
Configurations
Atoms
Ions
N: 1s2 2s2 2p3
+ 3 e-
N3-: 1s2 2s2 2p6
O: 1s2 2s2 2p4
+ 2 e-
O2-: 1s2 2s2 2p6
F: 1s2 2s2 2p5
+ 1 e-
F1-: 1s2 2s2 2p6
Ne: 1s2 2s2 2p6
Na: 1s2 2s2 2p6 3s1
- 1 e-
Na1+: 1s2 2s2 2p6
Mg: 1s2 2s2 2p6 3s2
- 2 e-
Mg2+: 1s2 2s2 2p6
- 3 e-
Al3+: 1s2 2s2 2p6
Al: 1s2 2s2 2p6 3s2 3p1
Ions and Their Electron
Configurations
• Transition element ions formed by
– 1st losing their valence electrons
– 2nd losing d-orbital electrons to obtain the
charge
• Fe2+
• Ag+
Fe3+
Zn2+
Co2+
Co4+
Anomalous Electron Configurations
• A few exceptions to the Aufbau
principles exist. Stable configuration:
– half-filled d shell:
• Cr has [Ar]4s13d5;
• Mo has [Kr] 5s14d5
– filled d subshell:
• Cu has [Ar]4s13d10
• Ag has [Kr]5s14d10.
• Au has [Xe]6s14f145d10
• Exceptions occur with larger elements
where orbital energies are similar.
Ions and Their Electron
Configurations
Atoms
Ions
Fe: [Ar] 4s2 3d6
- 2 e-
Fe2+: [Ar] 3d6
Fe: [Ar] 4s2 3d6
- 3 e-
Fe3+: [Ar] 3d5
Ionic Radii
• Effect of charge on ionic radii evaluated using
atomic size and Zeff
– Atomic size increases with increasing energy
levels
– Zeff
• Cation – more protons than electrons – stronger
attraction
• Anion – less protons than electrons – weaker attraction
• Cation < Neutral atom < anion
Ionic Radii
Ionic Radii
Atomic Radius
• Atomic radii actually
decrease across a row
in the periodic table.
Due to an increase in
the effective nuclear
charge.
• Within each group
(vertical column), the
atomic radius tends to
increase with the period
number.
Ionization Energy
Ionization Energy (Ei): The amount of energy
necessary to remove the highest-energy electron
from an isolated neutral atom in the gaseous state.
Ionization Energy
Ionization Energy
Boron has a lower Ei due to a smaller Zeff
(shielding by the 2s electrons)
Ionization Energy
Oxygen has a lower Ei since the first
electron is removed from a filled orbital
Higher Ionization Energies
M + energy
M1+ + e-
M1+ + energy
M2+ + e-
M2+ + energy
M3+ + e-
Problem
• Which of the following elements has the
smallest first ionization energy?
– A.
– B.
– C.
– D.
– E.
Rb
Mg
I
As
F
Problem
• Which of the following elements has the
largest second ionization energy (IE2)?
– A.
– B.
– C.
– D.
– E.
Li
B
O
F
Na
Electron Affinity
• Electron Affinity (Eea) - Describes the energy
associated with the absorption of 1 mole of
electrons by 1 mole of gaseous atoms
– Cl + e-
Cl-
– Can be positive or negative
• Positive – energy had to be added to force the atom to
absorb the electron (non-favored)
• Negative – energy was given off when the electron was
added to the atom (favored)
Electron Affinity
Electron Affinity (Eea): The energy released when
a neutral atom gains an electron to form an anion.
Problem
• Select the element with the most
negative electron affinity (i.e., accepts
an electron most readily).
– A.
– B.
– C.
– D.
– E.
H
Li
C
F
Ne
Trends in Size, IE, and EA
• IE, and EA are the opposite of atomic radius
Larger
Size
Ionization
energy
Electron
Affinity
Larger
Larger
Larger
Larger
Larger
Ionic Bonds and the Formation
of Ionic Solids
• Calculate the lattice energy (in kJ/mol) for the
formation of CaH2 from its elements.
• Calculate the overall energy change (in kJ/mol) for
the formation of CaCl from its elements.
• Calculate the overall energy change (in kJ/mol) for
the formation of CaCl2 from its elements.
• Which is more likely to form, CaCl or CaCl2?
Ionic Bonds and the Formation
of Ionic Solids
• Trends in Lattice Energy
– Increases with increasing charge
– Increases with decreasing ion size
Ionic Bonds and the Formation
of Ionic Solids
1s2 2s2 2p6 3s1
1s2 2s2 2p6 3s2 3p5
Na + Cl
Na1+
1s2 2s2 2p6
Cl11s2 2s2 2p6 3s2 3p6
Ionic Bonds and the Formation
of Ionic Solids
Born-Haber Cycle
Ionic Bonds and the Formation
of Ionic Solids
Born-Haber Cycle
Step 1:
Na(s)
Step 2:
1
Cl2(g)
2
Step 3:
Na(g)
Step 4:
Cl(g) + e-
Step 5:
Na1+(g) + Cl1-(g)
1
Na(s) + Cl2(g)
2
Na(g)
Cl(g)
+107.3 kJ/mol
+122 kJ/mol
Na1+(g) + e-
+495.8 kJ/mol
Cl1-(g)
-348.6 kJ/mol
NaCl(s)
-787 kJ/mol
NaCl(s)
-411 kJ/mol
Lattice Energies in Ionic Solids
Lattice Energy (U): The amount of energy that
must be supplied to break up an ionic solid into
individual gaseous ions.
The Octet Rule
Octet Rule: Main-group elements tend to undergo
reactions that leave them with eight outer-shell
electrons.
The Octet Rule
Octet Rule: Main-group elements tend to undergo
reactions that leave them with eight outer-shell
electrons.
Metals tend to have low Ei and low Eea.
They tend to lose one or more electrons.
Nonmetals tend to have high Ei and high Eea.
They tend to gain one or more electrons.
The Octet Rule
• Electrons of metals are most likely lost
due to the fact that:
– core electrons are shielding them from the
nucleus
– Zeff is lower
– Small ionization energies
– Upon loss they obtain noble gas
configuration
The Octet Rule
• Nonmetals are most likely to gain
electrons due to the fact that:
– no additional shielding occurs from the
nucleus occurs due to core electrons
– Zeff is higher
– More negative electron affinities
– Upon gain they obtain noble gas
configuration
The Octet Rule