1. Ionic Bonds and Some Main-Group Chemistry
Chapter 6
Ionic Bonds and Some Main-Group Chemistry

2. 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
Nonmetals when combined with metals gain electrons to form anions
The number gained = 8 – group #
WHY???????

3. Ions and Their Electron Configurations
Main Group Elements - the number of electrons gained or lost = the number of electrons necessary to obtain the nearest noble gas or pseudo-noble gas configuration (filled d-orbital).
Main group metal – the # electrons lost often = # of valence electrons
Nonmetal – the # electrons gained = # of electrons necessary to achieve 8 in the valence shell
Na, Ne, Na+ O, Ne, O2-
K, Ar, K+ Cl, Ar, Cl-
Ga, Ga3+ Sn, Sn4+

4. 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+ Fe3+ Co2+ Co4+
Ag+ Zn2+

5. Problem
Select the correct set of quantum numbers (n, l, ml, ms) for the first electron removed in the formation of a cation for strontium, Sr. 
A.  5, 1 , 0, -½
B.  5, 1, 0, ½
C.  5, 0, 1, ½
D.  5, 1, 1, ½
E.  5, 0, 0, -½

6. 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

7. Ionic Radii

8. Ionization Energy
Ionization Energy (Ei) – the energy required by 1 mole of gaseous atoms for 1 mole of electrons to be ejected.
Na EI Na+ + e-
Energy necessary to make a cation
More energy required for smaller atoms

9. Ionization Energy

10. Ionization Energy Trend
Increases across a period – held tighter
Decreases down a group – larger (n)

11. Higher Ionization Energies
Ionization energy not limited to a single electron
2nd electron removed requires even more energy
Removal of first leads to more protons than electrons
To break into a noble gas configuration requires a lot of energy because of their stability

12. Problem
Which one of the following equations correctly represents the process relating to the ionization energy of X? 
A.  X(s) → X+(g) + e-
B.  X2(g) → X+(g) + X-(g)
C.  X(g) + e- → X-(g)
D.  X-(g) → X(g) + e-
E.  X(g) → X+(g) + e-

13. Problem
Which of the following elements has the smallest first ionization energy? 
A.  Rb
B.  Mg
C.  I
D.  As
E.  F

14. Problem
Which of the following elements has the largest second ionization energy (IE2)? 
A.  Li
B.  B
C.  O
D.  F
E.  Na

15. 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)

16. Electron Affinity

17. Electron Affinity Trend Eea becomes more negative across a period
Eea becomes more positive down a group
Larger atoms don’t care as much

18. Problem
Which one of the following equations correctly represents the process involved in the electron affinity of X? 
A.  X(g) → X+(g) + e-
B.  X+(g) → X+(aq)
C.  X+(g) + e- → X(g)
D.  X(g) + e- → X-(g)
E.  X+(g) + Y-(g) → XY(s)

19. Problem
Select the element with the most negative electron affinity (i.e., accepts an electron most readily). 
A.  H
B.  Li
C.  C
D.  F
E.  Ne

20. Ionic Bonds and the Formation of Ionic Solids
Form when an element with a small Ei value comes in contact with an element with a negative Eea value.

21. Ionic Bonds and the Formation of Ionic Solids
The energetics of ionic reactions can be viewed on a Born–Haber Cycle which shows how each step contributes to the overall reaction energy.
That energy is called the lattice energy (U) of the solid. By convention, the lattice energy refers to the breakup of the crystal into ions.

22. Ionic Bonds and the Formation of Ionic Solids
Born–Haber Cycle for NaCl:

23. Ionic Solids and the Formation of Ionic Compounds
Born–Haber Cycle for MgCl2:

24. 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?

25. Ionic Bonds and the Formation of Ionic Solids
Trends in Lattice Energy
Increases with increasing charge
Increases with decreasing ion size

26. The Octet Rule General Conclusions
Group 1A form +1 by losing ns1 electron to obtain noble gas configuration
Group 2A form +2 by losing ns2 electrons to obtain noble gas configuration
Group 3A tend to form +3 by losing ns2np1 electrons to obtain noble gas configuration
Group 7A gain 1 electron to form ns2np6 hence giving them a noble gas configuration
Group 8A neither gain nor lose electrons because of stability of configuration

27. The Octet Rule
Octet Rule – main group elements tend to undergo reactions that leave them with 8 outer shell electrons
Why does the rule work?

28. 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

29. 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

30. Optional Homework
Text – 6.30, 6.36, 6.38, 6.40, 6.42, 6.44, 6.46, 6.48, 6.58, 6.64, 6.66
Chapter 6 Homework

31. Required Homework
Assignment 6