CH 8: Electron Configuration Renee Y. Becker Valencia Community College CHM

Electron Configuration of Atoms Rules of Aufbau Principle: Lower n orbitals fill first. Each orbital holds two electrons; each with different m s. Half-fill degenerate orbitals before pairing electrons. (p, d, & f)    NOT   __ 3p x 3p y 3p z 2

Electron Configuration of Atoms 3

Element DiagramConfiguration Li (Z = 3)   1s 2 2s 1 1s 2s Be (Z = 4)   1s 2 2s 2 1s 2s B (Z = 5)    __ __1s 2 2s 2 2p 1 1s 2s 2p x 2p y 2p z C (Z = 6)     __1s 2 2s 2 2p 2 1s 2s 2p x 2p y 2p z 4

Electron Configuration of Atoms Element Diagram Configuration O (Z = 8)      1s 2 2s 2 2p 4 1s 2s 2p x 2p y 2p z Ne (Z = 10)      1s 2 2s 2 2p 6 1s 2s 2p x 2p y 2p z S (Z = 16)          1s 2s 2p x 2p y 2p z 3s 3p x 3p y 3p z 1s 2 2s 2 2p 6 3s 2 3p 6 or [Ne] 3s 2 3p 6 abbreviations using the noble gases valence vs. core electrons 5

Electron Configuration of Atoms 6

Tc (Z = 43) [Kr] 5s 2 4d 5 Technetium Ni (Z = 28) [Ar] 4s 2 3d 8 7

Electron Configuration of Atoms 8

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Example 1: Electron Config. And NG Abb. 1.Sodium 2.Titanium 3.Argon 10

Anomalous Electron Configurations 19 of the predicted configurations from the periodic table are wrong –Largely due to unusual stability of both half-filled and fully filled subshells Cr (Z=24) expected configuration: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 4      __ 4s 3d 3d 3d 3d 3d actual configuration: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 3d 5    4s 3d 3d 3d 3d 3d 11

Atomic Radii 12

Atomic Radii ½ the distance between the nuclei of two identical atoms when they are bonded together. 13

Example 2: Ionic Radii Which of the following in each pair has a larger atomic radius? 1.Carbon or Fluorine 2.Chlorine or Iodine 3.Sodium or Magnesium 4.O or O 2- 5.Ca or Ca 2+ 14

Example 3: Quantum Numbers and Electron Configuration What are the 4 quantum numbers for the following? Remember you are only interested in the last electron!! 1.C 2.Na + 3.S 4.N 3- 15

Main Groups 16

Ions and their Electron Configuration Main-group metals donate electrons from the atom’s highest-energy occupied atomic orbital. –Na: 1s 2 2s 2 2p 6 3s 1 = [Ne] 3s 1 –Na + : 1s 2 2s 2 2p 6 = [Ne] –Mg: 1s 2 2s 2 2p 6 3s 2 = [Ne] 3s 2 –Mg 2+ : 1s 2 2s 2 2p 6 = [Ne] –Al:1s 2 2s 2 2p 6 3s 2 3p 1 = [Ne] 3s 2 3p 1 –Al 3+ 1s 2 2s 2 2p 6 = [Ne] 17

Ions and their Electron Configuration Main-group nonmetals accept electrons into their lowest-energy unoccupied atomic orbital. –N: 1s 2 2s 2 2p 3 = [He] 2s 2 2p 3 –N 3– : 1s 2 2s 2 2p 6 = [He] 2s 2 2p 6 = [Ne] –O: 1s 2 2s 2 2p 4 = [He] 2s 2 2p 4 –O 2– : 1s 2 2s 2 2p 6 = [He] 2s 2 2p 6 = [Ne] –F:1s 2 2s 2 2p 5 = [He] 2s 2 2p 5 –F – :1s 2 2s 2 2p 6 = [He] 2s 2 2p 6 = [Ne] 18

Example 4: Electron config. and NG Abb. 1.Cl - 2.F - 3.Ca 2+ 4.Na + 19

Ionic Radii or size Atoms shrink when an electron is removed to form a cation –Dec. # of shells –Inc. Z eff : Less electrons, less shielding, outer electrons more attracted to nucleus, therefore smaller more compact 20

Ionic Radii or size Atoms expand when converted to anions –III Ans 2 np 1 __ __ __ –IV Ans 2 np 2 __ __ __ –V Ans 2 np 3 __ __ __ –VI Ans 2 np 4 __ __ __ –VII Ans 2 np 5 __ __ __ Adding one electron to each of these will not add another shell it will just fill an already occupied p subshell Therefore the expansion is due to the decrease in Z eff and the increase in the electron-electron repulsions 21

Ionization Energy, E i The amount of energy needed to remove the highest-energy electron from an isolated neutral atom in the gaseous state Increase 22

Ionization Energy, E i Some exceptions/irregularities to general trend –E i Be > E i B we would expect opposite –Be 4 e 1s 2 2s 2 –B 5 e 1s 2 2s 2 2p 1 2s is closer to nucleus than 2p, Z eff for Be is stronger 2s is held more tightly and is harder to remove 23

Ionization Energy, E i E i N > E i O we would expect opposite N 7e 1s 2 2s 2 2p 3 __ __ __ O 8e 1s 2 2s 2 2p 4 __ __ __ Only difference is that an electron is being removed from a half-filled orbital (N) and one from a filled orbital (O) –Electrons repel each other and tend to stay as far apart as possible, electrons that are forced together in a filled orbital are slightly higher in energy so it is easier to remove one Therefore O < N 24

Higher Ionization Energy, E i1234… Ionization is not limited to one electron M + Energy  M + + eE i1 M + + Energy  M 2+ + eE i2 M 2+ + Energy  M 3+ + eE i3 Larger amts. Of energy are needed for each successive ionization, harder to remove an electron from a positively charger cation The energy differences between successive steps vary from one element to another. Why? EC 25

Higher Ionization Energy, E i1234… Easy to remove an electron from a partially filled valence shell Difficult to remove an electron from a filled valence shell Large amount of stability associated with filled s & p subshells Na: 1s 2 2s 2 2p 6 3s 1 Mg: 1s 2 2s 2 2p 6 3s 2 Cl:1s 2 2s 2 2p 6 3s 2 3p 5 26

Electron Affinity, E ea Energy change that occurs when an electron is added to an isolated atom in the gaseous state. The more neg. the E ea the greater the tendency of the atom to accept an electron Group 7A (halogens) have the most neg. E ea, high Z eff and room in valence shell Group 2A and 8A have near zero or slightly positive E ea 27

Alkali Metals Group 1A –Metallic –Soft –Good Conductors –Low MP –Lose 1 elec in redox, powerful reducing agent –Very reactive –Not found in elemental state in nature 28

Alkaline Earth Metals Group 2A –Harder, but still relatively soft –Silvery –High MP than group 1A –Less reactive than group 1A –Lose 2 e in redox, powerful reducing agent –Not found in elemental form in nature 29

Group 3A All but Boron –Silvery –Good conductor –Relatively soft –Less reactive than 1A & 2A 30

Halogens Group 7A –Non-metals –Diatomic molecules –Tend to gain e during redox 31

Noble Gases Group 8A –Colorless, odorless, unreactive gases –Ns 2 np 6 Makes it difficult to add e or remove e 32

Octet Rule Group 1A tends to lose their ns 1 valence shell electron to adopt a noble gas electron config. Group 2A lose both ns 2 “ “ Group 3A lose all three ns 2 np 1 “ “ Group 7A Gains one electron to attain NG Group 8A inert, rarely lose or gain electrons 33