1. Chapter 3 Electronic Structure and the Periodic Law

2. Learning Objectives
Locate elements in the periodic table on the basis of group and period designations
Determine the number of electrons in designated atomic orbitals, subshells, or shells
Determine the number of valence shell electrons and the electronic structure for atoms, and relate this information to the location of elements in the periodic table
Determine the following for elements: the electronic configuration of atoms, the number of unpaired electrons in atoms, and the identity of atoms based on provided electronic configurations

3. Learning Objectives (continued)
Determine the shell and subshell locations of the distinguishing electrons in elements, and based on their location in the periodic table, classify elements into the categories given in Figures 3.10 and 3.12

4. Periodic Law
Statement about the behavior of the elements when they are arranged in a specific order
Present form - Elements with similar chemical properties occur at regular (periodic) intervals when the elements are arranged in order of increasing atomic numbers

5. Periodic Table
Arrangement of the elements in a table based on the periodic law
In a modern periodic table, elements with similar chemical properties are found in vertical columns called groups or families
18 groups/families
7 periods

6. Group or Family of the Periodic Table
Designations
The U.S. system uses a Roman numeral and a letter (either A or B) at the top of the column
The IUPAC (but not universally used) system uses only a number from 1 to 18

7. Period of the Periodic Table
Horizontal row of elements arranged according to increasing atomic numbers
Numbered from top to bottom

8. Modern Periodic Table
Elements 58–71 and 90–103 are not placed in their correct periods but are located below the main table

9. Group and Period Identification
Elements and the periodic table
Each element belongs to a group and period of the periodic table
Examples of group and period location for elements
Calcium, Ca, element 20: group IIA(2), period 4
Silver, Ag, element 47: group IB(11), period 5
Sulfur, S, element 16: group VIA(16), period 3

10. Example 3.1 - Groups and Periods of the Periodic Table
Identify the group and period to which each of the following belongs P Cr
Element number 30
Element number 53

11. Example 3.1 - Solution Phosphorus (P) is in group VA(15) and period 3
Chromium (Cr) is in group VIB(6) and period 4
Element with atomic number 30 is zinc (Zn), which is found in groups IIB(12) and period 4
Element number 53 is iodine (I), found in group VIIA(17) and period 5

12. Bohr's Theory
Bohr proposed that the electron in a hydrogen atom moved in any one of a series of circular orbits around the nucleus
Electron could change orbits only by absorbing or releasing energy
Absorption moves electrons to higher-energy orbits
Release moves electrons to lower-energy orbits

13. Quantum Mechanical Model
Precise paths of electrons moving around the nucleus cannot be determined accurately
Location and energy of electrons around a nucleus is specified using shell, subshell, and orbital

14. Shell
Location and energy of electrons around a nucleus that is designated by a value for n
Value of n can be 1, 2, 3, etc.
Higher n values for a shell correspond to higher energies and greater distances from the nucleus for the electrons of the shell

15. Subshell Each shell is made up of one or more subshells
Designated by a letter from the group s, p, d, and f
Combination of shell number and subshell letter of the subshell is used to identify subshells
For example, a p subshell located in the fourth shell (n = 4) would be referred to as a 4p subshell

16. Subshell (continued)
Number of subshells located in a shell is the same as the number of the shell
Shell number 3 (n = 3) contains three subshells, designated 3s, 3p, and 3d
Electrons located in a subshell are identified by using the same designation as the subshell
Electrons in a 3d subshell are called 3d electrons

17. Atomic Orbitals
Volume of space around atomic nuclei in which electrons of the same energy move
Groups of orbitals with the same n value form subshells
Have different shapes, depending on the energy of the electrons they contain
All s subshells consist of a single s orbital
All p subshells consist of three p orbitals
All d subshells consist of five d orbitals
All f subshells consist of seven f orbitals

18. Figure 3.3 - Shapes of Typical s, p, and d Orbitals

19. Atomic Orbitals (continued)
According to the quantum mechanical model, all types of atomic orbitals can contain a maximum of two electrons
Single d orbital can contain a maximum of two electrons, and a d subshell that contains five d orbitals can contain a maximum of 10 electrons

20. Energy of Electrons Increases with increasing n value
Electron in the third shell (n = 3) has more energy than an electron in the first shell (n = 1)
For equal n values but different subshells, the energy of electrons in orbitals increases in the order s, p, d, and f
4p electron has more energy than a 4s electron

21. Table 3.1 - Relationship between Shells, Subshells, Orbitals, and Electrons

22. Example 3.3 - Shells and Subshells of Atoms
Determine the following for the third shell of an atom:
Number of subshells
Designation for each subshell
Number of orbitals in each subshell
Maximum number of electrons that can be contained in each subshell
Maximum number of electrons that can be contained in the shell

23. Example Solution
Number of subshells is the same as the number used to designate the shell
Therefore, the third shell contains three subshells
Subshells increase in energy according to the order s, p, d, f
Subshells in the shell are therefore designated 3s, 3p, and 3d
Number of orbitals in the subshells is 1, 3, and 5 because s subshells always contain a single orbital, p subshells always contain three orbitals, and d subshells always contain five orbitals

24. Example 3.3 - Solution (continued)
Each atomic orbital can contain a maximum of electrons, independent of the type of orbital under discussion
Therefore, the 3s subshell (one orbital) can hold a maximum of two electrons, the 3p subshell (three orbitals) a maximum of 6 electrons, and the 3d subshell (five orbitals) a maximum of 10 electrons
Maximum number of electrons that can be contained in the shell is simply the sum of the maximum number for each subshell, = 18

25. Join In (2)
Correct Answer
1. shell

26. Join In (3) Which of the following can contain 10 electrons?
4s orbital
5p subshell
shell 2
3d subshell
Correct Answer
4. 3d subshell

27. Valence Shell
Outermost (highest-energy) shell of an element that contains electrons
Atoms with the same number of electrons in the valence shell have similar elemental chemical properties
Members of Group IIA(2)

28. Table 3.2 - Electron Occupancy of Shells

29. Electron Shell Occupancy
What do magnesium and calcium have in common?
2 electrons in valence shell
What predictions can be made about the number of electrons in strontium's valence shell?
Sr has similar chemical properties to Mg and Ca, so it is likely to have 2 electrons in its valence shell
What other element on this chart has similar properties to Mg, Ca, and Sr?
Beryllium

30. Example 3.4 - Number of Electrons in Valence Shells for Atoms
Referring to Table 3.2, indicate the number of electrons in the valence shell of elements in groups IA(1), IIA(2), IIIA(13), and IVA(14)

31. Example Solution
According to Table 3.2, the elements in group IA(1) are hydrogen, lithium, sodium, and potassium
Each element has one electron in the valence shell
Hydrogen belongs in group IA(1) on the basis of its electronic structure, but its properties differ significantly from other group members
Group IIA(2) elements are beryllium, magnesium, and calcium
Each has two electrons in the valence shell
Group IIIA(13) elements are boron and aluminum
Both have three electrons in the valence shell
Group IVA(14) elements are carbon and silicon
Each has four valence-shell electrons

32. Electronic Configurations
Detailed arrangement of electrons in atoms indicated by a specific notation, 1s22s22p4, etc.
Occupied subshells are indicated by their identifying number and letter such as 2s and the number of electrons in the subshell is indicated by the superscript on the letter
Thus, in 1s22s22p4, the 2s2 notation indicates that the 2s subshell contains two electrons

33. Subshell-Filling Order
Electrons will fill subshells in the order of increasing energy of the subshells
A 1s subshell will fill before a 2s subshell
Order must obey Hund's rule and the Pauli exclusion principle

34. Hund's Rule
Electrons will not join other electrons in an orbital if an empty orbital of the same energy is available for occupancy
Thus, the second electron entering a p subshell will go into an empty p orbital of the subshell rather than into the orbital that already contains an electron

35. Pauli Exclusion Principle
Electrons behave as if they spin on an axis
Only electrons spinning in opposite directions (indicated by ↑ and ↓) can occupy the same orbital within a subshell

36. Filling Order
When it is remembered that each orbital of a subshell can hold a maximum of two electrons and that Hund's rule and the Pauli exclusion principle are followed, it results in the following filling order for the first 10 electrons:
H He Li Be B C N Ne

37. Figure 3.7 - Relative Energies and Electron-Filling Order for Shells and Subshells

38. Electron-Filling Order for Shells and Subshells
Filling order for any number of electrons is obtained by following the arrows in the diagram
Shells are represented by large rectangles
Subshells are represented by colored rectangles
Orbitals within the subshells are represented by circles

39. Filling Order Memory Aid
Diagram provides a compact way to remember the subshell filling order
Correct order is obtained by following the arrows from top to bottom of the diagram, going from the arrow tail to the head, and then from the next tail to the head, etc.

40. Filling Order Memory Aid (continued)
Maximum number of electrons each subshell can hold must be remembered
s subshells can hold 2
p subshells can hold 6
d subshells can hold 10
f subshells can hold 14

41. Filling Order and Periodic Table
Order of subshell filling matches the order of subshell blocks on the periodic table if the fill occurs in the order of increasing atomic numbers

42. Electron Configuration Example
The following electronic configurations result from the correct use of any of the diagrams given earlier
Magnesium, Mg, 12 electrons: 1s22s22p63s2
Silicon, Si, 14 electrons: 1s22s22p63s23p2
Iron, Fe, 26 electrons: 1s22s22p63s23p64s23d6
Gallium, Ga, 31 electrons: 1s22s22p63s23p64s23d104p1

43. Noble Gas Configurations
With the exception of helium, all noble gases (group VIIIA) have electronic configurations that end with completely filled s and p subshells of the highest occupied shell
Can be used to write electronic configurations in an abbreviated form in which the noble gas symbol enclosed in brackets is used to represent all electrons found in the noble gas configuration

44. Noble Gas Configurations: Example
Magnesium: [Ne]3s2
Symbol [Ne] - Represents the electronic configuration of neon, 1s22s22p6
Iron: [Ar]4s23d6
Symbol [Ar] - Represents the electronic configuration of argon, 1s22s22p63s23p6
Gallium: [Ar]4s23d104p1

45. Example 3.6 - Electronic Configurations and Unpaired Electrons
Write the electronic configuration for an atom that contains 7 electrons, and indicate the number of unpaired electrons

46. Example 3.6 - Solution Correct filling order of subshells is:
1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p
Even though s subshells can hold 2 electrons, p subshells 6, d subshells 10, and f subshells 14, only enough subshells to hold 7 electrons will be used
Therefore, the configuration is written as shown, starting on the left, with circles representing orbitals and arrows representing electrons
It is apparent that no subshells beyond 2p are needed because that subshell contains only 3 electrons

47. Example 3.6 - Solution (continued)
Note that both the 1s and 2s subshells are full; the 2p subshell is half-full, with one electron in each of the three orbitals (Hund's rule)
These three electrons are unpaired
1s2 2s2 2p3

48. Example 3.7 - Abbreviated Electronic Configurations
Write abbreviated electronic configuration for an atom that contains 7 electrons

49. Example Solution
From Example 3.6, the configuration is 1s22s22p3
Two electrons in the 1s subshell represent the noble gas configuration of helium (He), so the configuration can be written as [He]2s22p3

50. Join In (7)
Which of the following electron configurations matches aluminum?
[Ne]3s23p1
[Ne]3p3
[Ar]3p5
[Ar]3s22p1
Correct Answer
1. [Ne] 3s2 3p1

51. Classification of Elements
Representative element: Element in which the distinguishing electron is found in an s or a p subshell
Transition element: Element in which the distinguishing electron is found in a d subshell
Inner-transition element: Element in which the distinguishing electron is found in an f subshell

52. Figure 3.12 - Locations of Metals, Nonmetals, and Metalloids in the Periodic Table

53. Metals and Nonmetals Metals
Elements found in the left two-thirds of the periodic table
Properties - High thermal and electrical conductivities, high ductility and malleability, and metallic luster
Nonmetals
Elements found in the right one-third of the periodic table
Properties - Opposite those of metals and occur as brittle, powdery solids or as gases

54. Metalloids
Elements that form a diagonal separation zone between metals and nonmetals in the periodic table
Have properties between those of metals and nonmetals and often exhibit some characteristic properties of each type

55. Example 3.8 - Distinguishing Electrons and Element Classifications
Use the periodic table and Figures 3.9 and 3.10 to determine the following for Ca, Fe, S, and Kr
Type of distinguishing electron
Classification based on Figure 3.10

56. Example Solution
On the basis of the location of each element in Figure 3.9, the distinguishing electrons are of the following types:
Ca: s Fe: d S: p Kr: p
Classifications based on figure 3.10 are:
Ca - Representative element
Fe - Transition element
S - Representative element
Kr - Noble gas