Chapter 5: Electrons In Atoms

Wave Nature of Light Electromagnetic Radiation – form of energy that exhibits wavelike behaviors as it travels through space Ex: visible light, microwaves, x-rays, radio, etc.

Wavelength Symbol – λ (lambda) Defn – distance between equivalent points on a curve λ λ λ

Frequency Symbol – f Defn – number of waves that pass a given point in a second Unit: Hertz (Hz) Ex: 300 Hz = 300 1/s = 300 s -1 = 1/s= s -1

Amplitude Defn – wave’s height from origin to crest origin crest amplitude

Electromagnetic Waves All EM waves travels at the speed of light (c) c = 3 x 10 8 m/s c = (wavelength)(frequency) c = λf = 3 x 10 8 m/s

Wavelength and Frequency Relationship Inversely related: as one increases, other decreases short λ long λ high frequency low frequency

Electromagnetic Spectrum Defn – shows all forms of electromagnetic radiation

Ex problem #1 What is the wavelength of a microwave with a frequency of 3.44 x 10 9 s -1 ? c = λf λ = c f = 3 x10 8 m/s 3.44 x 10 9 s -1 = 8.72 x m

Ex problem #2 What is the frequency of green light, which has a wavelength of 4.90 x m? = c = λf f = c λ 3 x10 8 m/s 4.90 x m = 6.12 x Hz

Particle Nature of Light Quantum – minimum amount of energy that can be gained or lost by an atom Photoelectric Effect – emission of electrons from metal’s surface when light of specific frequency shines on surface METAL light e-e-

Photon – particle of light Photon Energy –U–Unit: joules (J) –f–formula h = Planck’s constant = x J·s f = frequency (s -1 ) E photon = hf

Ex problem What is the energy of a photon from the violet portion of the rainbow if it has a frequency of 7.23 x s -1 ? E = hf = (6.626 x J·s)(7.23 x s -1 ) = 4.79 x J

Bohr Model of an Atom Ground State – lowest energy state of an atom Excited State – state when atom gains energy **pay attention to the electrons** Bohr Model – shows electron orbit and energy level of an electron

Bohr Model E1E1 E2E2 E3E3 E 1 = lowest energy level E 3 > E 2 > E 1

Ground State to Excited State in ground state, no energy radiated in excited state, electrons jump to higher energy level electron go from high E level to low E level photon emitted Energy of atom ) 2) 3) 4)

Atomic Orbitals Defn – 3D region around nucleus describing specific electron’s location

Principle Quantum Number (n) Defn – indicates the energy level an electron is on - use periodic table to tell (look at rows) n = 1,2,3,…..

Principal Quantum Number

Energy Sublevels/Orbitals Defn – shape of orbital that tells the path of the electrons 4 sublevels: s, p, d, f Let’s focus on the s and p orbitals

s orbital Shape: electrons travel in a sphere

s orbital 1s 2s 3s The greater the energy level, the bigger the orbital

p orbital Shape: dumbbell or figure 8 shaped

Electron Configuration Defn – arrangement of electrons in an atom Where are certain electrons located?

Rules Governing Electron Configurations 1) Aufbau Principle – electrons occupy lowest energy orbital available - fill up level 1 first, then level 2, etc. 2) Pauli Exclusion Principle – there is a max number of electrons that occupy a single orbital (2)

Rules Governing Electron Configurations 3) Hund’s Rule – if orbitals have equal energy, one e - will go in each orbital before doubling up

Blocks On Periodic Table s d p f s

Divisions of Orbitals s orbital – 1 sublevel (2 e - max) p orbital – 3 sublevels (6 e - max) d orbital – 5 sublevels (10 e - max) f orbital – 7 sublevels (14 e - max)

Orbital Diagram Nitrogen How many electrons? What energy level is nitrogen on? n = 2 7 1s2s2p

Orbital Diagram Silicon How many electrons? What energy level is silicon on? n = s2s2p3s3p

Orbital Diagram Copper How many electrons? What energy level is copper on? n = s2s2p3s3p 4s3d

Electron Configuration Notation Oxygen (8 e - ) Sulfur (16 e - ) Vanadium (23 e - ) Zirconium (40 e - ) 1s 2s2p 224 1s 2s2p 226 3s3p 24 1s 2s2p 226 3s3p 26 4s 2 3d 3 1s 2s2p 226 3s3p 26 4s 2 3d 10 4p5s 22 4d 6

Noble Gas Notation Rule: start from previous noble gas, then write the configuration Oxygen Sulfur Vanadium Zirconium [He] 2s2p 24 [Ne] 3s3p 24 [Ar] 4s3d 23 [Kr] 5s4d 22

Valence Electrons defn – electrons in outer most energy level - located in highest s & p orbitals (max 8) N: Mg: Se: 2s2p 23 1s 2 5 valence e - 2s2p 26 1s 2 3s 2 2 valence e - 2s2p 26 1s 2 3p4s 62 3s 2 3d4p valence e -

Electron Dot Structure Defn – shows number of valence e - by diagram Nitrogen (5 v.e.) Magnesium (2 v.e.) Selenium (6 v.e.) N Mg Se