Electrons in Atoms Big Idea #2 Electrons and the Structure of Atoms Chemistry I Notes Ch. 5 Electrons in Atoms Big Idea #2 Electrons and the Structure of Atoms

5.1 Revising the Atomic Model The Bohr Model of the Atom Electrons occupy specific energy levels in atoms. These energy levels are identified by a principle quantum number – n (1-7) When electrons occupy the lowest energy levels available the atom is in its ground state. When electrons occupy higher energy levels than the ground state the atom is in an excited state. When atoms absorb energy the electrons jump to higher energy levels (excited state). When they drop back down to the ground state these atoms emits light of specific wavelength corresponding to the energy change of the electron (emission spectra)

5.1 Revising the Atomic Model Louis De Broglie (1924) proposed that particles of matter have wavelike character Heisenberg’s Uncertainty Principle – The position and speed of an electron cannot be measured simultaneously. If you measure one you can’t know the other. So electrons are located based on the probability of finding them in a region of space around an atom (orbital).

5.2 Electron Arrangement in Atoms Quantum Mechanical Model – Treats the electron as a wave with quantized energy and explains the behavior of atoms. Electrons occupy a cloud where the probability of finding an electron is highest where the cloud is densest. Orbitals – a region around the nucleus where an electron with a given amount of energy is likely to be found. Maximum capacity is 2 electrons.

Orbitals and Energy Electrons are found in primary energy levels sublevels and orbitals Primary energy level – quantum number n where n = 1-7 (floor of hotel) Sublevels – Each primary energy level has the number of sublevels equal to its n quantum number they are labeled s, p, d, & f (wing of hotel) s sublevels contain only 1 s orbital that can hold 2 electrons p sublevels contain 3 p orbitals that can hold 6 electrons d sublevels contain 5 d orbitals that can hold 10 electrons f sublevels contain 7 f orbitals that can hold 14 electrons

1s Orbital

Representation of the 4f Orbitals in Terms of Their Boundary Surfaces

The Boundary Surfaces of All of the 3d Orbitals

The Boundary Surface Representations of All Three 2p Orbitals

Orbitals and Energy cont… Orbitals contain only 2 electrons s orbital – spherical shape 1 per energy level p orbital – dumbell shaped 3 per energy level d orbital – double dumbell shaped 5 per energy level f orbital – very complex shapes 7 per energy level Electrons within an orbital have opposite spin – Pauli Exclusion Principle

Orbital Energies

Electron Capacities of Shells and Orbitals Primary energy Level 1 2 3 4 5 6 7 Orbital Type s s p s p d s p d f Electron Capacity 2 6 2 6 10 2 6 10 14 Total Electrons 8 18 32

Quantum Numbers and Electrons If the primary energy level is given as n=1-7 Then the number of sublevels in that primary energy level = n The number of orbitals in that energy level = n2 The number of electrons in that energy level= 2n2

5.2 Electron Arrangement in Atoms cont… Electron configurations are determined by distributing the atom’s electrons into energy levels, sublevels , and orbitals based on a set of principles. Aufbau Principle –Electrons are added one at a time to the lowest energy orbitals available until all electrons are accounted for. Pauli Exclusion Principle – Orbitals hold a maximum of 2 electrons with opposite spin. Hund’s Rule – Electrons occupy equal-energy orbitals so that a maximum number of unpaired electrons results (college dorm rule). Fill electrons into sublevels 1 per orbital until all orbitals have 1 then double up. Remember the exceptions at Copper and Chromium

Energy Level Positions For The First Twenty Elements 1S

5.3 Atomic Emission Spectra Light has properties of both waves and particles. Light is a form of electromagnetic radiation – electric and magnetic fields oscillating at right angles to each other. Wave Characteristics Amplitude – height of wave from origin to peak (m) Wavelength -  -Distance between successive crests (m) Frequency –  - cycles per second (Hz) Speed – c- distance per unit time Light= 3x108 m/s Speed = frequency x wavelength c=  

The Nature of Waves

Electromagnetic Waves Click in this box to enter notes. Go to Slide Show View (press F5) to play the video or animation. (To exit, press Esc.) This media requires PowerPoint® 2000 (or newer) and the Macromedia Flash Player (7 or higher). [To delete this message, click inside the box, click the border of the box, and then press delete.] Copyright © Houghton Mifflin Company. All rights reserved.

Problem Calculate the wavelength of ultra violet light with a frequency of 2.00X1016 Hz?

5.3 Atomic Spectra cont… LIGHT: What Is It? Light Energy Atoms As atoms absorb energy, electrons jump out to a higher energy level. Electrons release light when falling down to the lower energy level. Photons - bundles/packets of energy released when the electrons fall. Light: Stream of Photons

5.3 Atomic Spectra cont… Quantum – Restriction on the amount of energy an object emits or absorbs (Max Planck) E= h where E is the energy of a photon in joules (j) h is Planck’s constant 6.62x10-34 j-s  is the frequency in hertz (Hz) or 1/s Energies absorbed or emitted by atoms are quantized Photoelectric Effect- electrons ejected from the surface of a metal when light shines on it. For every metal there is a minimum frequency of light needed to release electrons. This quantum of energy is called a photon. (Albert Einstein) Thus light has particle wave duality

Problem What is the energy of a photon of Infrared light with a wavelength of 1.00x10-5 m ? First calculate frequency using c=λv then calculate energy using E=hv

5.3 Atomic Spectra cont… Types of spectra Line Spectra – contain only specific wavelengths or colors – atoms emit these when their electrons are excited. Continuous Spectrum – white light broken into all its colors R-O-Y-G-B-I-V (rainbow) Absorption spectra – Black lines on the continuous spectra of star light that represent fingerprints of the elements present.

Refraction of White Light

The Line Spectrum of Hydrogen