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, O 2- K, Ar, K + Cl, Ar, Cl - Ga, Ga 3+ Sn, Sn 4+ –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 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 6s 6p 6d 6f The periodic table can also be used to determine the electron configuration of an element.

Ions and Their Electron Configurations + 3 e e e e e e - N: O: F: Na: Mg: Al: 1s 2 2s 2 2p 3 1s 2 2s 2 2p 4 1s 2 2s 2 2p 5 1s 2 2s 2 2p 6 3s 1 1s 2 2s 2 2p 6 3s 2 1s 2 2s 2 2p 6 3s 2 3p 1 N 3- : O 2- : F 1- : Ne: Na 1+ : Mg 2+ : Al 3+ : 1s 2 2s 2 2p 6 IonsAtoms

Ions and Their Electron Configurations Transition element ions formed by –1 st losing their valence electrons –2 nd losing d-orbital electrons to obtain the charge Fe 2+ Fe 3+ Co 2+ Co 4+ Ag + Zn 2+

Anomalous Electron Configurations A few exceptions to the Aufbau principles exist. Stable configuration: –half-filled d shell: Cr has [Ar]4s 1 3d 5 ; Mo has [Kr] 5s 1 4d 5 –filled d subshell: Cu has [Ar]4s 1 3d 10 Ag has [Kr]5s 1 4d 10. Au has [Xe]6s 1 4f 14 5d 10 Exceptions occur with larger elements where orbital energies are similar.

Ions and Their Electron Configurations - 2 e e - Fe: [Ar] 4s 2 3d 6 Fe 2+ : Fe 3+ : [Ar] 3d 6 [Ar] 3d 5 IonsAtoms

Ionic Radii Effect of charge on ionic radii evaluated using atomic size and Z eff –Atomic size increases with increasing energy levels –Z eff Cation – more protons than electrons – stronger attraction Anion – less protons than electrons – weaker attraction Cation < Neutral atom < anion

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 (E i ): The amount of energy necessary to remove the highest-energy electron from an isolated neutral atom in the gaseous state.

Ionization Energy

Boron has a lower E i due to a smaller Z eff (shielding by the 2s electrons)

Ionization Energy Oxygen has a lower E i since the first electron is removed from a filled orbital

Higher Ionization Energies M 3+ + e - M 2+ + energy M 1+ + e - M + energy M 2+ + e - M 1+ + energy

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

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

Electron Affinity Electron Affinity (E ea ) - 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 (E ea ): 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. H –B. Li –C. C –D. F –E. Ne

Trends in Size, IE, and EA IE, and EA are the opposite of atomic radius Larger Size Ionization energy Larger Electron Affinity

Ionic Bonds and the Formation of Ionic Solids Calculate the lattice energy (in kJ/mol) for the formation of CaH 2 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 CaCl 2 from its elements. Which is more likely to form, CaCl or CaCl 2 ?

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 Na 1+ Na 1s 2 2s 2 2p 6 Cl+ 1s 2 2s 2 2p 6 3s 2 3p 6 3s13s1 3p53p5 1s 2 2s 2 2p 6 1s 2 2s 2 2p 6 3s 2 Cl 1-

Ionic Bonds and the Formation of Ionic Solids Born-Haber Cycle

Ionic Bonds and the Formation of Ionic Solids Born-Haber Cycle Step 2:Cl(g)Cl 2 (g)+122 kJ/mol Step 5: NaCl(s)Na(s) + Cl 2 (g)-411 kJ/mol 2 1 Step 1:Na(g)Na(s) kJ/mol Step 3:Na 1+ (g) + e - Na(g) kJ/mol Step 4:Cl 1- (g)Cl(g) + e kJ/mol NaCl(s)Na 1+ (g) + Cl 1- (g)-787 kJ/mol 2 1

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 Metals tend to have low E i and low E ea. They tend to lose one or more electrons. Nonmetals tend to have high E i and high E ea. They tend to gain one or more electrons. Octet Rule: Main-group elements tend to undergo reactions that leave them with eight outer-shell electrons.

The Octet Rule Electrons of metals are most likely lost due to the fact that: – core electrons are shielding them from the nucleus –Z eff 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 –Z eff is higher –More negative electron affinities –Upon gain they obtain noble gas configuration

The Octet Rule