1. Lecture 2: Atoms and Elements
Electron Energy Levels
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2. Electron Energy Levels
Electrons are arranged in
specific energy levels that
Are labeled n = 1, n = 2, n = 3, and so on.
Increase in energy as n increases.
Have the electrons with the lowest energy in the first energy level (n=1)closest to the nucleus.
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3. Energy Level Changes
An electron absorbs energy to “jump” to a higher energy level.
When an electron falls to a lower energy level, energy is emitted.
In the visible range, the emitted energy appears as a color.
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4. Energy Emitted LecturePLUS Timberlake
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5. Sublevels Sublevels Contain electrons with the same energy.
Are found within each energy level.
Are designated by the letters s, p, d, f.
The number of sublevels is equal to the value of the principal quantum number (n).
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6. Quantum Numbers and Atomic Orbitals
An atomic orbital is specified by three quantum numbers.
n the principal quantum number - a positive integer
l the angular momentum quantum number - an integer from 0 to n-1
ml the magnetic moment quantum number - an integer from -l to +l

7. Number of Sublevels LecturePLUS Timberlake
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8. Table 7.2 The Hierarchy of Quantum Numbers for Atomic Orbitals
Name, Symbol
(Property)
Allowed Values
Quantum Numbers
Principal, n
(size, energy)
Positive integer
(1, 2, 3, ...) 1 2 3 1 2
Angular momentum, l
(shape)
0 to n-1 1 +1 +2 -1 -2 -1 +1 -1 +1
Magnetic, ml
(orientation)
-l,…,0,…,+l

9. Sample Problem 7.6
Determining Quantum Numbers for an Energy Level
PROBLEM:
What values of the angular momentum (l) and magnetic (ml) quantum numbers are allowed for a principal quantum number (n) of 3? How many orbitals are allowed for n = 3?
PLAN:
Follow the rules for allowable quantum numbers found in the text.
l values can be integers from 0 to n-1; ml can be integers from -l through 0 to + l.
SOLUTION:
For n = 3, l = 0, 1, 2
For l = 0 ml = 0
For l = 1 ml = -1, 0, or +1
For l = 2 ml = -2, -1, 0, +1, or +2
There are 9 ml values and therefore 9 orbitals with n = 3.

10. Sample Problem 7.7
Determining Sublevel Names and Orbital Quantum Numbers
PROBLEM:
Give the name, magnetic quantum numbers, and number of orbitals for each sublevel with the following quantum numbers:
(a) n = 3, l = 2
(b) n = 2, l = 0
(c) n = 5, l = 1
(d) n = 4, l = 3
PLAN:
Combine the n value and l designation to name the sublevel. Knowing l, we can find ml and the number of orbitals.
SOLUTION: n l
sublevel name
possible ml values
# of orbitals
(a) 3 2 3d
-2, -1, 0, 1, 2 5
(b) 2 2s 1
(c) 5 1 5p
-1, 0, 1 3
(d) 4 3 4f
-3, -2, -1, 0, 1, 2, 3 7

11. Sample Problem 7.8
Identifying Incorrect Quantum Numbers
PROBLEM:
What is wrong with each of the following quantum numbers designations and/or sublevel names? n l ml
Name
(a) 1 1 1p
(b) 4 3 +1 4d
(c) 3 1 -2 3p
SOLUTION:
(a) n = 1 only l = 0. Name 1s.
(b) l = 3 is an f sublevel. Name 4f.
(c) l = 1 can only have ml of -1, 0, +1.

12. Energy of Sublevels In any energy level,
The s sublevel has the lowest energy.
The s sublevel is followed by the p, d, and f sublevels in order of increasing energy.
Higher sublevels are possible, but only s, p, d, and f sublevels are needed to hold the electrons in the atoms known today.
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13. Orbitals
An orbital
Is a three- dimensional space around a nucleus where an electron is most likely to be found.
Has a shape that represents electron density (not a path the electron follows).
Can hold up to 2 electrons.
Contains two electrons that must spin in opposite directions.
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14. s Orbitals An s orbital Has a spherical shape around the nucleus.
Increases in size around the nucleus as the energy level n value increases.
Is a single orbital found in each s sublevel.
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15. p Orbitals A p orbital Has a two-lobed shape.
Is one of three p orbitals that make up each p sublevel.
Increases in size as the value of n increases.
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16. Figure 7.20
One of the seven possible 4f orbitals.

17. Sublevels and Orbitals
Each sublevel consists of a specific number of
orbitals.
An s sublevel contains one s orbital.
A p sublevel contains three p orbitals.
A d sublevel contains five d orbitals.
An f sublevel contains seven f orbitals.
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18. Electrons in Each Sublevel
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19. Lecture 2: Atoms and Elements
Electron Configurations
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20. Order of Filling Energy levels are filled with electrons
In order of increasing energy.
Beginning with quantum number n = 1.
Beginning with s followed by p, d, and f.
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21. Energy Diagram for Sublevels
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22. Orbital Diagrams An orbital diagram shows
Orbitals as boxes in each sublevel.
Electrons in orbitals as vertical arrows.
Electrons in the same orbital with opposite spins (up and down vertical arrows).
Orbital diagram for Li
1s s p
filled half-filled empty
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23. Order of Filling Electrons in an atom
Fill orbitals in sublevels of the same type with one electron until half full,
Then pair up in the orbitals using opposite spins.
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24. Writing Orbital Diagrams
The orbital diagram
for carbon consists of
Two electrons in the 1s orbital.
Two electrons in the 2s orbital.
One electron each in two of the 2p orbitals
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25. Individual Learning Check
Write the orbital diagrams for
A. Nitrogen
B. oxygen
C. magnesium
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26. Electron Configuration
An electron configuration
Lists the sublevels filling with electrons in order of increasing energy.
Uses superscripts to show the number of electrons in each sublevel.
For neon (10 electrons) is as follows:
number of electrons
sublevel s2 2s2 2p6
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27. Example: Period 1 Configurations
In Period 1, the first two electrons enter the 1s orbital
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28. Abbreviated Configurations
An abbreviated configuration shows
The symbol of the noble gas in brackets that represents completed sublevels.
The remaining electrons in order of their sublevels,
Example: Chlorine has a configuration of
1s2 2s2 2p6 3s2 3p5
[Ne]
The abbreviated configuration for chlorine is
[Ne] 3s2 3p5
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29. Period 2 Configurations
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30. TAPPS Learning Check
A. The correct electron configuration for nitrogen is
1) 1s2 2p ) 1s2 2s2 2p6 3) 1s2 2s2 2p3
B. The correct electron configuration for oxygen is
1) 1s2 2p ) 1s2 2s2 2p4 3) 1s2 2s2 2p6
C. The correct electron configuration for calcium is
1) 1s2 2s2 2p6 3s2 3p6 3d2
2) 1s2 2s2 2p6 3s2 3p6 4s2
3) 1s2 2s2 2p6 3s2 3p8
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31. TAPPS Learning Check A. Cl B. S C. K
Write the electron configuration and abbreviated configuration for each of the following elements:
A. Cl
B. S
C. K
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32. Sublevel Blocks on the Periodic Table
The periodic table consists of sublevel blocks
arranged in order of increasing energy.
Groups 1A-2A = s level
Groups 3A-8A = p level
Groups 3B to 2B = d level
Lanthanides/Actinides = f level
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33. Sublevel Blocks LecturePLUS Timberlake
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34. Writing Electron Configurations
Using the periodic table, write the electron configuration
for silicon.
Solution
Silicon is in group 4A, period 3, thus we would stop at 3p and it would have 2 electrons in the 3p orbital:
all the sublevel blocks in order gives:
1s2 2s2 2p63s2 3p2
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35. Electron Configurations d Sublevel
The 4s orbital has a lower energy than the 3d orbitals.
In potassium K, the last electron enters the 4s orbital instead of the 3d
1s 2s 2p 3s 3p 3d 4s
Ar 1s s2 2p6 3s2 3p6
K 1s s2 2p6 3s2 3p6 4s1
Ca 1s s2 2p6 3s2 3p6 4s2
Sc 1s s2 2p6 3s2 3p6 3d1 4s2
Ti 1s s2 2p6 3s2 3p6 3d2 4s2
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36. Exceptions in Sublevel Block Order
Within the filling of the 3d sublevel, exceptions occur for chromium and copper
Both Cr and Cu, in the 3d sublevel, are close to either a half-filled or filled sublevel
Cr has only 1 electron in the 4s and 5 e-s in the 3d sublevel …half-filled 3d, added stability
Cu has 1 e- in 4s and 10 e-s in 3d sublevel … completely filled 3d, stable
After 4s and 3d, 4p is filled

37. Writing Electron Configurations
Using the periodic table, write the electron configuration
for manganese.
Solution
1s2 2s2 2p63s2 3p6 4s2 3d5
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38. Learning Check A. The last two sublevel blocks in the electron
configuration for Co are
1) 3p64s2
2) 4s24d7
3) 4s23d7
B. The last three sublevel blocks in the electron
configuration for Sn are
1) 5s25p24d10
2) 5s24d105p2
3) 5s25d105p2
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39. Learning Check Give the symbol of the element that has A. [Ar]4s2 3d6
B. Four 3p electrons
C. Two electrons in the 4d sublevel
D. The element that has the electron configuration
1s2 2s2 2p6 3s2 3p6 4s2 3d2
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40. Pause: ALE 2
Group activity: all groups work on problems on ALE 2 worksheet, problems 12-15
Need volunteers to work on the problems written on the board. If no volunteers immediately, will call names. Everyone will do problems on the board sooner or later
While working on the problems, ask if you have any questions. I’m more than happy to help
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41. Lecture 2: Atoms and Elements
Periodic Trends
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42. Valence Electrons The valence electrons
Determine the chemical properties of the elements.
Are the electrons in the highest energy level.
Are related to the Group number of the element.
Example: Phosphorus has 5 valence electrons
5 valence electrons
P Group 5A(15) s2 2s2 2p6 3s2 3p3
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43. Groups and Valence Electrons
All the elements in a group have the same number of
valence electrons.
Example: Elements in Group 2A(2) have two (2) valence electrons.
Be 1s2 2s2
Mg 1s2 2s2 2p6 3s2
Ca [Ar] 4s2
Sr [Kr] 5s2
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44. Periodic Table and Valence Electrons

45. Electron-Dot Symbols · Mg · or Mg · or · Mg or · Mg
An electron-dot symbol
Indicates valence electrons
as dots around the symbol of the element.
Of Mg shows two valence electrons as single dots on the sides of the symbol Mg.
· Mg · or Mg · or · Mg or · Mg
Electron-dot symbol
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46. Writing Electron-Dot Symbols
The electron-dot symbols for
Groups 1A(1) to 4A(14) use single dots.
· ·
Na · · Mg · · Al · · C ·
Groups 5A(15) to 7A(17) use pairs and single dots.
· · · ·
· P · : O ·
· ·
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47. Learning Check State the number of valence electrons for each: A. O
1) ) 6 3) 8
B. Al
1) ) 3 3) 1
C. Cl
1) 2 2) 5 3) 7
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48. Learning Check State the number of valence electrons for each.
A. 1s2 2s2 2p6 3s2 3p1
B. 1s2 2s2 2p6 3s2
C. 1s2 2s2 2p5
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49. Groups and Electron-Dot Symbols
In a group, all the electron-dot symbols have the same number of valence electrons (dots).
Example: Atoms of elements in Group 2A(2) each have 2 valence electrons.
2A(2)
· Be ·
· Mg ·
· Ca ·
· Sr ·
· Ba ·
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50. Learning Check  A. X is the electron-dot symbol for 1) Na 2) K 3) Al
 
B.  X 
 is the electron-dot symbol of
1) B 2) N 3) P
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51. Atomic Size Atomic size is Described using the atomic radius.
The distance from
the nucleus to the
valence electrons.
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52. Atomic Radius Within A Group
Increases going down each group of representative elements.
Decreases going across each period.
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53. Ionization Energy Ionization energy
Is the energy it takes to remove a valence electron.
Na(g) + Energy (ionization) Na+(g) + e-
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54. Ionization Energy The ionization energies of Metals are low
Nonmetals are high
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55. Pause: Group Work
Do all the problems in group activity 2 as group