2. Atomic Spectra and Bohr Bohr said classical view is wrong. Need a new theory — now called QUANTUM or WAVE MECHANICS. e- can only exist in certain discrete orbits e- is restricted to QUANTIZED energy state (quanta = bundles of energy)

3. Bohr’s Hydrogen Atom: A Planetary Model

4. B. Bohr’s Hydrogen Atom 1. Energy Levels (Orbits): – Each allowed orbit is assigned a principal quantum number (n = 1,2,3,…  ). – The energy of the electron and the radius of its orbit increase as the value of n increases. – An atom with its electron in the lowest energy level is said to be in the ground state.

5. a) Excited State vs. Ground State Absorb energy to move to a higher energy orbit. Emit energy to move to a lower energy orbit.

6. Arrangement of Electrons in Atoms Electrons in atoms are arranged as LEVELS (n) 1-7 periodic table SUBLEVELS (l) s,p,d,f ORBITALS (m l ) 1 3 5 7

7. Electron Energy Level (Shell) Principle Quantum number Generally symbolized by n, it denotes the probable distance of the electron from the nucleus. “n” is also known as the Principle Quantum number n is 1 through 7 because 7 periods Number of electrons that can fit in a shell: 2n 2 1 st energy level N=1 2(1) 2 = 2 2 nd energy level N=2 2(2) 2 = 8 3 rd energy level N=3 2(3) 2 = 18 4 th energy level N=4 2(4) 2 = 32 5 th energy level N=5 2(5) 2 = 50 6 th energy level N=6 2(6) 2 = 72 7 th energy level N=7 2(7) 2 = 98

8. Energy Levels n = 1 n = 2 n = 3 n = 4 n = 5 n = 6 n = 7

9. Types of Orbitals The most probable area to find these electrons takes on a shape The most probable area to find these electrons takes on a shape So far, we have 4 shapes. They are named s, p, d, and f. So far, we have 4 shapes. They are named s, p, d, and f. No more than 2 e- assigned to an orbital – one spins clockwise, one spins counterclockwise No more than 2 e- assigned to an orbital – one spins clockwise, one spins counterclockwise First e- drawn upward, second e- drawn down First e- drawn upward, second e- drawn down

10. The s orbital has a spherical shape centered around the origin of the three axes in space. s Orbital shape Every energy level has S orbital. HOLDS 2 e- 1s 2s 3s

11. There are three dumbbell-shaped p orbitals in each energy level above n = 1, each assigned to its own axis (x, y and z) in space. 2s 2p 3p 4p 7p p orbital shape

12. The shapes and labels of the five d orbitals. Holds 2 e- each. No d orbitals on level 1 & 2 3s 3p 3d Finally, f sublevel has 7 orbitals

13. Orbitals and the Periodic Table Orbitals grouped in s, p, d, and f sublevels Orbitals grouped in s, p, d, and f sublevels s orbitals p orbitals d orbitals f orbitals

14. THREE RULES for e- configuration AUFBAU principal- electrons occupy the orbitals of lowest energy first. start at 1s PAULI exclusion principal- an atomic orbital holds a maximum of TWO e-, each with opposite spin. HUND’S rule- in orbitals of EQUAL ENERGY (p,d,f), place one e- in each orbital before making any pairs. All single e- spin the same way.

15. Aufbau diagram: Filling order

16. Orbital box notation b) An orbital box notation shows all sublevels, orbitals and the spins of the electrons. P 1s 2 2s 2 2p 2 2p 2 2p 2 3s 2 3p 1 3p 1 3p 1 P The orbital box diagram indicates that the three electrons in the 3p subshell all have parallel (unpaired) spins.   1s1s 2s2s2p2p3s3s3p3p RULES FOR FILLING: 1. One arrow represents one electron. 2. First arrow upward, 2 nd arrow down 3. Fill in order of Aufbau diagram 4. Assign 1 e- to each box in an orbital, then go back and assign rest..

17. LithiumLithium Group 1A Atomic number = 3 1s 2 2s 1 ---> 3 total electrons

18. CarbonCarbon Group 4A Atomic number = 6 1s 2 2s 2 2p 2 ---> 6 total electrons 6 total electrons Here we see for the first time HUND’S RULE. When placing electrons in a set of orbitals having the same energy, we place them singly as long as possible.

19. Draw these orbital diagrams! Oxygen (O) Chromium (Cr) Mercury (Hg)

20. Electron config. notation The electron configuration notation of an atom is a shorthand method of writing the location of electrons by sublevel. (order by Aufbau diagram) The sublevel is written followed by a superscript with the number of electrons in the sublevel. – If the 2p sublevel contains 2 electrons, it is written 2p 2

21. Writing Electron Configurations First, determine how many electrons are in the atom. Iron has 26 electrons. Arrange the energy sublevels according to increasing energy (Aufbau diagram) – 1s 2s 2p 3s 3p 4s 3d … Fill each sublevel with electrons until you have used all the electrons in the atom: – Fe: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 6 The sum of the superscripts equals the atomic number of iron (26)

22. Let’s Try It! Write the electron configuration for the following elements: H Li N Ne K Zn Pb

23. EXPANDED ELECTRON CONFIGURATION notation In some cases, it is more informative to write a list of each occupied orbital and indicate the number of electrons in each orbital. N1s 2 2s 2 2p 3 versusN 1s 2 2s 2 2p 1 2p 1 2p 1 The expanded configuration indicates that there is one electron in each of the three 2p orbitals – the original configuration doesn’t.

24. Write the expanded electron configuration and the box orbital notation for oxygen (1s 2 2s 2 2p 4 ). O1s 2 2s 2 2p 4 O

25. Write the expanded electron configuration and the box orbital notation for boron (1s 2 2s 2 2p 1 ). B 1s 2 2s 2 2p 1 B

26. Order of Subshell Filling using Periodic Table You don’t have to memorize the order of the subshells, just use the periodic table! Start at H & move through the table in order until the desired element is reached. Notice: (n – 1)d orbitals are filled after ns and before np orbitals.

27. Shorthand Notation A way of abbreviating long electron configurations Since we are only concerned about the outermost electrons, we can skip to places we know are completely full (noble gases 8A column), and then finish the configuration

28. Shorthand Notation Step 1: Find the closest noble gas (8A column) to the atom (or ion), WITHOUT GOING OVER the number of electrons in the atom (or ion). Write the noble gas in brackets [ ]. Step 2: Find where to resume by finding the next energy level. Step 3: Resume the configuration until it’s finished.

29. Noble Gas Core Shorthand Notation Recall, the electron configuration for Na is: Na: 1s 2 2s 2 2p 6 3s 1 We can abbreviate the electron configuration by indicating the innermost electrons with the symbol of the preceding noble gas. The preceding noble gas with an atomic number less than sodium is neon, Ne. We rewrite the electron configuration: Na: [Ne] 3s 1

30. Practice Shorthand Notation Write the shorthand notation for each of the following atoms: Cl K Ca I Bi

31. e- configs & valence e- A list of all the electrons in an atom (or ion) Must go in order (Aufbau principle) 2 electrons per orbital, maximum We need electron configurations so that we can determine the number of electrons in the outermost energy level. These are called valence electrons. The number of valence electrons determines how many and what this atom (or ion) can bond to in order to make a molecule 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6 6s 2 4f 14 … etc.

32. Valence Electrons When an atom undergoes a chemical reaction, only the outermost electrons are involved. These electrons are of the highest energy and are furthest away from the nucleus. We need e- configurations so we can determine the number of e- in the outermost energy level. These are the valence electrons. The number of valence e- determines how many and what this atom (or ion) can bond to in order to make a molecule The valence electrons are the s and p electrons beyond the noble gas core.

33. Valence Electrons The valence e- are the last s and p electrons beyond the noble gas core Electrons are divided between core and valence electrons B 1s 2 2s 2 2p 1 Core = [He], valence = 2s 2 2p 1 Br [Ar] 3d 10 4s 2 4p 5 Core = [Ar] 3d 10, valence = 4s 2 4p 5

34. Electron Dot Formulas An electron dot formula of an elements shows the symbol of the element surrounded by its valence electrons. We use one dot for each valence electron. Consider phosphorous, P, which has 5 valence electrons. Here is the method for writing the electron dot formula.

38. a) Order of Subshell Filling i) Using the Periodic Table Write the electron configuration for Al. Al Ne

39. iv) Valence Electrons The atomic electron configuration of an element determines the chemical reactivity of that element, but it is not the total number of electrons that is important. If that were the case, each element would have unique reactivity & we would not observe periodicity in atomic trends and reactivity. How do we explain the trends in the periodic table? Valence Electrons!

40. v) Lewis Dot Symbols The number of valence electrons in an atom is directly related to its reactivity. Gilbert Lewis came up with a way to represent an element & its valence electrons. One dot equals one valence electron.

41. The periodic table can be used as a guide for electron configurations. The period number is the value of n. Groups 1A and 2A have the s-orbital filled. Groups 3A - 8A have the p-orbital filled. Groups 3B - 2B have the d-orbital filled. The lanthanides and actinides have the f-orbital filled. Electron Configurations and the Periodic Table

42. Relative sizes of the spherical 1s, 2s, and 3s orbitals of hydrogen.

43. Types of Orbitals ( l ) s orbital p orbital d orbital

44. Diagonal Rules s 3p 3d s 2p s 4p 4d 4f s 5p 5d 5f 5g? s 6p 6d 6f 6g? 6h? s 7p 7d 7f 7g? 7h? 7i? 1234567 Steps: 1.Write the energy levels top to bottom. 2.Write the orbitals in s, p, d, f order. Write the same number of orbitals as the energy level. 3.Draw diagonal lines from the top right to the bottom left. 4.To get the correct order, follow the arrows! By this point, we are past the current periodic table so we can stop.

45. s orbitals d orbitals Number of orbitals Number of electrons p orbitals f orbitals How many electrons can be in a sublevel? Remember: A maximum of two electrons can be placed in an orbital.

46. Electron Configurations 2p 4 Energy Level Sublevel Number of electrons in the sublevel 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6 6s 2 4f 14 … etc.

47. Rules of the Game No. of valence electrons of a main group atom = Group number (for A groups) Atoms like to either empty or fill their outermost level. Since the outer level contains two s electrons and six p electrons (d & f are always in lower levels), the optimum number of electrons is eight. This is called the octet rule.

48. Blocks and Sublevels We can use the periodic table to predict which sublevel is being filled by a particular element.

49. Condensed Electron Configurations Neon completes the 2p subshell. Sodium marks the beginning of a new row. So, we write the condensed electron configuration for sodium as Na: [Ne] 3s 1 [Ne] represents the electron configuration of neon. Core electrons: electrons in [Noble Gas]. Valence electrons: electrons outside of [Noble Gas]. Electron Configurations

50. Predicting Valence Electrons The Roman numeral in the American convention indicates the number of valence electrons. – Group IA elements have 1 valence electron – Group VA elements have 5 valence electrons When using the IUPAC designations for group numbers, the last digit indicates the number of valence electrons. – Group 14 elements have 4 valence electrons – Group 2 elements have 2 valence electrons

51. B. Bohr’s Hydrogen Atom: A Planetary Model Bohr assumed that the single electron in a hydrogen atom moves around the nucleus in a circular orbit. Bohr applied quantum theory to his model by proposing that the electron is restricted to circling the nucleus in orbits of certain radii, each of which corresponds to a specific energy. Thus, the energy of the electron is quantized, and the electron is restricted to certain energy levels – orbits.

52. a) Excited State vs. Ground State Transitions Between Levels: Electrons can move from one energy level to another – An electron must absorb energy to transition from a lower energy level to a higher energy level – Energy is emitted when an electron transitions from a higher energy level to a lower energy level When an electron absorbs energy and moves to a higher energy level, that atom is said to be in an excited state. http://www.upscale.utoronto.ca/GeneralInterest/Harrison/BohrModel/Flash/BohrModel.html

53. Orbital shapes are defined as the surface that contains 90% of the total electron probability. An orbital is a region within an energy level where there is a probability of finding an electron. Electron Orbitals

54. p Orbitals The three p orbitals lie 90 o apart in space The three p orbitals lie 90 o apart in space

55. Orbital Diagrams One additional rule: Hund’s Rule – In orbitals of EQUAL ENERGY (p, d, and f), place one electron in each orbital before making any pairs – All single electrons must spin the same way I nickname this rule the “Monopoly Rule” In Monopoly, you have to build houses EVENLY. You can not put 2 houses on a property until all the properties have at least 1 house.

56. iv) Valence Electrons For elements in the first three periods: – The core electrons are those in the preceding noble gas configuration. – The additional electrons in the outer shell are the valence electrons. eg. B 1s 2 2s 2 2p 1 B [He]2s 2 2p 1 Core: 1s 2 Valence: 2s 2 2p 1 (Shell with n = 1)(Shell with n = 2)

57. Energy Levels Each energy level has a number called the PRINCIPAL QUANTUM NUMBER, n Each energy level has a number called the PRINCIPAL QUANTUM NUMBER, n Currently n can be 1 thru 7, because there are 7 periods on the periodic table Currently n can be 1 thru 7, because there are 7 periods on the periodic table

58. Orbital Diagrams Box representation of electron configuration One arrow represents one electron. First arrow upward, 2 nd arrow down

59. 1. Representations of Electron Configuration b) An orbital box notation shows all sublevels, orbitals and the spins of the electrons. P 1s 2 2s 2 2p 2 2p 2 2p 2 3s 2 3p 1 3p 1 3p 1 P The orbital box diagram indicates that the three electrons in the 3p subshell all have parallel (unpaired) spins.   1s1s 2s2s2p2p3s3s3p3p

61. Filling Diagram for Sublevels Aufbau Principle