Chapter 4-Arrangement of Electrons in Atoms Carbon:1s22s22p2

Photoelectric Effect(Early 1900’s) Photoelectric effect-Heated metal absorbs energy and causes electrons to get excited. Photon of energy-Particle of light that is carrying enough energy to excite an electron It takes a quantum of energy to excite an electron Quantum: The amount of energy needed to move an electron from one energy level to the next. - Woohoo!! Photon Quantum of energy

Relationship between an Atom and Energy Ground State: The lowest energy state of an atom. Absorb- When an atom receives energy then it Absorbs energy. Excited State: The state in which an atom has absorbed energy. The electrons are further away from the nucleus. Emit- When an atom gives off energy then it is emitting energy.

How did Bohr use the photoelectric effect to come up with fixed energy levels? With Rutherford’s model, all amounts of energy should have caused the photoelectric effect to happen but only certain amounts of energy actually do, therefore, there must be levels for the electrons to try and reach. Also, You get distinct color bands which suggests that electrons are jumping to and from specific places (and releasing specific amounts of energy) and not just randomly buzzing around the nucleus.

Bohr Model Niels Bohr -developed a model of a hydrogen atom that showed the electron circling the nucleus in a fixed path. He determined that each energy level had a particular amount of electrons that could occupy each level. 2 things wrong with Bohrs Model: It only worked for Hydrogen why? It didn’t explain the atoms bonding ability or chemical behavior

Bohr vs Quantum Models + 3rd Energy Level 2nd Energy Level 1st energy level

The Quantum Model Heisenberg Uncertainty Principle-It is impossible to know both the position and velocity of an electron at the same time. Mice and Cockroaches!! Quantum Model-Model that shows the possible or probable location of all electrons in an atom Orbitals- three dimensional region around the nucleus that indicates the probable location of an electron. 90% of the time

Quantum Numbers Quantum Numbers- 4 numbers used to tell us where an electron is located in an atom 1. Principal Quantum Number (n) 2. Angular Momentum Quantum Number ( l ) 3. Magnetic Quantum Number 4. Spin Quantum Number

Our Goal: Electron Configurations Noble Gas Configuration H 1s1 He 1s2 Li 1s22s1 Be 1s22s2 B 1s22s22p1 C 1s22s22p2 N 1s22s22p3 O 1s22s22p4 F 1s22s22p5 Ne 1s22s22p6 H 1s1 He 1s2 Li [He]2s1 Be [He]2s2 B [He]2s22p1 C [He]2s22p2 N [He]2s22p3 O [He]2s22p4 F [He]2s22p5 Ne [He]2s22p6

1-Principal Quantum # Tells us which energy level an electron is in Symbolized by n Can have a value of 1,2,3,4,5,6,or 7 Example n=3 means the electron is in the 3rd energy level.

2-Angular Momentum Quantum # Gives the shape of the orbital the electrons are making s, p, d, or f

#2-Angular Momentum s Orbital spherical or round shape (like a ball) Can hold 2 electrons total Lowest in energy Periodic table Groups 1-2

#2-Angular Momentum p Orbital p orbital can have THREE orientations(parts) -orientated on the x axis -orientated on the y axis -orientated on the z axis dumbbell shaped Each dumbell can hold 2 e- How many total electrons will be in a p orbital? Periodic table Groups 13-18 Second lowest in energy

#2-Angular Momentum d Orbital 5 different orientations (parts) Each part can hold 2 e- How many total electrons can a d orbital hold? Periodic table groups 3-12 Third in energy

#2-Angular Momentum f Orbital f Orbital can have 7 orientations Each shape can hold 2 e- How many total electrons can an f orbital hold? 14 total e- Shape not important Periodic table groups: Lanthanides and Actinides (the two rows at the bottom) Highest in energy

#2-Angular Momentum s Orbital s sublevel can have only ONE orientation or part spherical or round shape (like a ball) Can hold 2 electrons total Periodic table Groups 1-2 Lowest in energy

3-Magnetic Quantum # Tells us which plane, orientation, or axis the orbital is in

4-Spin Quantum # Tells us if the electron is spinning clockwise or counter-clockwise :We will use these with Orbital Notation Clockwise Counter Clockwise

Aufbau principle States that an electron occupies the lowest-energy Orbital that can receive it. Electrons take the path of least resistance..Lazy Electrons -

Hund’s Rule States that each part of an orbital should get 1 electron before any of the parts can have 2. Don’t be stingy you have to share!!! Each part of p,d, and f needs 1 electrons before any part can have 2.

Quantum Numbers Pauli Exclusion Principle: no two electrons in the same atom can have the same set of quantum #s. Ne 1s22s22p6

How to know where electrons fill? Electrons always fill lowest energy level first (1,2,3,4,5,6,7) Electrons fill lowest orbital in each energy level first (s,p,d,f) Question you need to answer in your notes: Why do electrons 21-30 go back down to the 3rd energy level and fill the d orbital?

Electron Configuration Chart

Representing Electron Configurations Four ways to show arrangement of electrons 1. Electron Configuration Notation(long) 2. Noble Gas Configuration(short cut) 3. Orbital Notation(arrows) 4. Electron Dot Notation(dots)

1-Electron Configuration(long way) Shows all electrons in atom Gives Energy Level Shape of Orbital Number of electrons in each orbital Example: Hydrogen 1S1 # of electrons Orbital Type Main Energy Level

How to write electron configurations Always start with 1s “Read” the periodic table like a book. Follow all the rules When you have to jump to the next energy level, ALWAYS start back filling in the s orbital. Remember that all energy levels have an s orbital.

Electron Configurations-period three elements Na 1s22s22p63s1 Mg 1s22s22p63s2 Al 1s22s22p63s23p1 Si 1s22s22p63s23p2 P 1s22s22p63s23p3 S 1s22s22p63s23p4 Cl 1s22s22p63s23p5 Ar 1s22s22p63s23p6

Fourth period elements K 1s22s22p63s23p64s1 Ca 1s22s22p63s23p64s2 Sc 1s22s22p63s23p64s23d1 Ti Zn Ga 1s22s22p63s23p64s23d104p1 Ge As Se Br Kr

Exception to every rule There are some exceptions to the Aufbau principal for elements 24 and 29 Cr: 1s2 2s2 2p6 3s2 3p6 4s1 3d5 Cu: 1s2 2s2 2p6 3s2 3p6 4s1 3d10

Elements of the fifth period Rb 1s22s22p63s23p64s23d104p65s1 Sr 1s22s22p63s23p64s23d104p65s2

Write the electron configuration notation for the following: 1. Boron (B) 2. Magnesium (Mg) 3. Argon (Ar) 4. Calcium (Ca) 5. Bromine (Br)

Noble gas configurations -A short hand way of writing an electron configuration using noble gases. -First, determine what period the element is in. -Second, put the noble gas in the previous period in [ ]. The noble gas in [ ]accounts for its atomic # of electrons.

Noble gas configurations Third-start filling with the energy level that equals the period #. Ex: write the noble gas configuration for sodium, Na Na is in the 3rd period, so use the noble gas in the 2nd period, which is Ne [Ne]3s1

Noble gas configurations Compare the configuration of the noble gas Ne to all of the period 3 elements. All period 3 elements start off with Neon’s configuration Ne 1s22s22p6 Na 1s22s22p63s1 Mg 1s22s22p63s2 Al 1s22s22p63s23p1 Si 1s22s22p63s23p2 P 1s22s22p63s23p3 S 1s22s22p63s23p4 Cl 1s22s22p63s23p5 Ar 1s22s22p63s23p6

Orbital Notation Coincides with electron configuration notation. Orbital notation is a diagram that shows Hund’s rule.

Preparing for the Test Go online to the Text Book Work the following problems to prepare: Page-124 (15-19) Page-125 (20-37) Page- 126 (38-41)

Dot notation Shows only valence shell (outer) electrons Group 1 has 1 valence electron Group 2 has 2 valence electrons Group 13 has 3 valence electrons Group 14 has 4 valence electrons Group 15 has 5 valence electrons Group 16 has 6 valence electrons Group 17 has 7 valence electrons Group 18 has 8 valence electrons - - - - -

Dot notation continued First-write the symbol of the element Second-determine the group of the element and decide # of outer electrons Third- Place dots around the symbol to represent electrons in the outer shell