LECTURE Seventeen CHM 151 ©slg TOPICS: 1. Electronic Configurations, Atoms 2. Electronic Configurations, Ions

Where the Final Electron Goes: s,f,d,p Blocks of Elements s f d p

Subshells by order of filling, Lowest energy to highest star t finish

Hydrogen, Z=1: “spectroscopic notation” 1s 1 Main shell subshell Total e’s in subshell “ orbital box diagram ” 1s

1s 2s 2p THE NEXT 4 ELEMENTS

1s 2s 2p 2p 2p End, Period 2

Note that Helium, 1s 2, and Neon, 1s 2 2s 2 2p 6, found at the end of the first two periods, have completed shell 1 and 2. They are classified as “noble or ‘inert’ gases”, all along with all elements in their periodic table group VIIIA. All remaining elements in this column, 8A, have completed an outer shell s and p subshell, 8 total outer shell electrons. This represents a special, very stable arrangement, ns 2 np 6, which is found to be a goal of elements in forming compounds: an outer shell of 8 e’s, like the noble gases.

In doing configurations, it is customary to do all electrons from the last noble gas as a summary of the core electrons: [He 2 ] [ Ne 10 ] [Ar 18 ] [ Kr 36 ] [Xe 54 ] [Rn 86 ] Nitrogen, Z = 7, becomes [He 2 ] 2s 2 2p 3 The electrons that are completing these configurations are called “core electrons”: once in place, they do not take place in reactions. The valence electrons, used for bonding, are those in subshells filling in between two noble gases.

Short form, from last noble gas Na, Z =11 [Ne 10 ] 3s 1 Electronic Configurations, the “Long form” Na, Z=11 1s 2 2s 2 2p 6 3s 1 1s 2 ) 2 2s 2 2p 6 ) 10 3s 1 My personal way of counting e’s using: a summary at end of each period Core electrons Valence electrons

Period 3: Valence e’sCore e’s

Subshells by order of filling, Lowest energy to highest don e next

At this point, a glance at the period table or a look at our list of (n+ l ) values tells us that the next subshell to be filled is not 3d but 4s: Potassium, Z=19, is in the first column of the s block, fourth period, and must be utilizing a 4s orbital for its “distinguishing electron.” The (n+ l ) sums or PT dictate that the filling is as follows:

A point of convention: It is standard practice to arrange the ordering of your electronic configurations in order of shells, not in actual order of filling. Sc, [ Ar 18 ]4s 2 3d 1 ORDER OF FILLING becomes, by convention: Sc, [Ar 18 ]3d 1 4s 2 ORDER OF SHELLS Order found in texts

Note exception!

When filling in electrons into the d and f subshells, we run into unexpected “irregularities”: configurations not quite what we would predict. In the “d” block, these occur principally in two locations, column 6B and column 1B: (6B) “d 4 s 2 ” “d 5 s 1 ” (1B) “d 9 s 2 ” “d 10 s 1 ” The half full and completed d orbital set is lower energy... In most cases:

Especially stable: half full or filled set of orbitals. We will meet many such exceptions in the f block! d5d5 d 10

Column 6B:

Column 1B:

After completion of the 3d subshell, we complete the 4th period by filling in distinguishing electrons into the 4p: End, Period 4

Electronic Configuration, Larger Atoms Suppose we wanted to do Bi, Z = 83: Note it is in period 6, column 5A, so must finish with “6p 3 ” Period 5: Repeats pattern, Period 4: 5s 2 4d 10 5p 6 Period 6: Adds first f subshell: 6s 2 4f 14 5d 10 6p 6

Bi, Z =83, 6th period, Column 5A 6p 3 1A 2A 3A 4A 5A 6A 7A 8A Period 6 Period 1

Bi, #83: period 6, column 5A “6p 3 ”, Long form, order of filling: 1s 2 ) 2 2s 2 2p 6 ) 10 3s 2 3p 6 ) 18 4s 2 3d 10 4p 6 ) 36 5s 2 4d 10 5p 6 ) 54 6s 2 4f 14 5d 10 6p 3 ) 83 Short form, Order of filling: [Xe 54 ] 6s 2 4f 14 5d 10 6p 3 Short form, Order of shells: [Xe 54 ] 4f 14 5d 10 6s 2 6p 3 (red e’s: valence electrons)

GROUP WORK Predict the electronic configuration for: Te, Z= 52: long, order of filling; short, order of filling short, order of shells La, Z= 57 short, order of filling short, order of shells Fr, Z= 87 short, order of filling short, order of shells Circle all valence electrons in short form, order of shells!

Key Te, Z= 52 (column 6A, period 5, “5p 4” ) Long: 1s 2 ) 2 2s 2 2p 6 ) 10 3s 2 3p 6 ) 18 4s 2 3d 10 4p 6 ) 36 5s 2 4d 10 5p 4 ) 52 Short, order of shells: [Kr 36 ] 4d 10 5s 2 5p 4 Note: Te is in column 6A, has 6 valence electrons, its “outer shell bonding e’s”

Fr, Z= 87 Short, order of filling or shells: [Rn 86 ]7s 1 Francium, like all column IA elements, has 1 valence electron

La, Z= 57 (Column 3B, period 6, 5d 1 ) Short, order of filling: [Xe 54 ]6s 2 5d 1 Short, order of shells: [Xe 54 ] 5d 1 6s 2 Note: La is in column 3B, has 3 valence electrons, its “outer shell bonding e’s” plus its “incomplete subshell electrons in lower shell” Transition elements use outer s’s and inner d’s for bonding

This configuration for La is an exception: it is expected to be [Xe 54 ]6s 2 4f 1 but experimental data (spectral lines) indicate that its correct assignment is the [Xe 54 ]6s 2 5d 1. La, Z= 57, [Xe 54 ] 5d 1 6s 2 Ce, Z= 58, [Xe 54 ] 4f 1 5d 1 6s 2 Pr, Z= 59, [Xe 54 ] 4f 3 6s 2 Nd, Z= 60, [Xe 54 ] 4f 4 6s 2 Eu, Z= 63, [Xe 54 ] 4f 7 6s 2 Dy, Z= 66, [Xe 54 ] 4f 10 6s 2 Yb, Z= 70, [Xe 54 ] 4f 14 6s 2 Lu, Z= 71, [Xe 54 ] 4f 14 5d 1 6s 2 Hf, Z= 72, [Xe 54 ] 4f 14 5d 2 6s 2 Check out Table 8.2, p345!

Electronic Configuration of Ions The electronic configurations we have developed give the basis for the charges we have already assigned to many elements when they are found as ions in an ionic type compound. The main group elements (columns 1A-8A) lose, gain or share valence electrons in forming compounds so that they can achieve an outer shell configuration, when possible, of the nearest noble gas.

When electrons are transferred from one element to another, charged particles called ions are formed. We have already assigned a positive charge, equal to the column number, for ions formed from elements in columns 1A, 2A and selected 3A elements. Note how this correlates with configurations we have done:

Since all 1A elements share the same outer shell configuration, “s 1 ”, they are all expected to form the same charged ion, +1. All elements in column 2A, with the outer shell configuration of “s 2 ” show a + 2 charge, losing both these electrons to form the noble gas configuration:

In the p block, elements filling the p subshell, both cations and anions are formed: Aluminum, in group 3A, loses outer s and p electrons to form a + 3 cation: End, Lecture 17