Chapter 28 The Atom

Objectives

• 28.1 Explain the structure of the atom • 28.1 Distinguish continuous spectra from a

line spectra • 28.1 Contrast emission and absorption spectra • 28.1 Solve problems using the orbital radius

and energy level equations

Objectives

• 28.2 Describe the shortcomings of the Bohr model of the atom

• 28.2 Describe the quantum model of the atom • 28.2 Explain how a laser works and describe

properties of laser light

Different Models of the Atom

• Dalton: Billiard Ball – Indivisable

• J.J. Thomson– Plum Pudding Model

• Rutherford– The Nuclear Model (Positive nucleus with orbiting

electrons)– Others have built on this model

Some Terms

• Alpha Particle: Helium Particle with a positive charge

• Emission Spectrum: Wavelengths emitted by an atom is called its – Absorption Spectrum: Same idea, but what

wavelengths are absorbed• Spectroscope: Used to determine the

wavelengths of visible light given off

• Continuous Spectrum produced by having very hot objects– A theoretical black

body produces a continuous spectrum

• Spectroscopy: Identifying elements by their emission spectrum or absorption spectrum

Red Shift: Moving Away Blue Shift: Moving Towards

Rutherford vs Bohr

• Rutherford: Electrons orbit like a planet orbits a star (Planetary model of the atom)

• Issues: Falling into nucleus, radiating all wavelengths

Bohr Model

• Energy Quantized: Electrons only fall when giving off energy

• Falls and jumps correspond to certain energies

Terms

• Energy Levels: Refers to the orbital's around the nucleus (Noted as n = 1, n = 2). Also called the Quantum Numbers

• Ground State: When an electron has the lowest energy level allowed

• Excited State: When an electron has absorbed energy and has moved to a higher orbital. Don’t last long (nanoseconds) at the level before falling

From Last Chapter

• hf (energy emitted) = Eexcited – Eground

• What wavelength of light is required to make hydrogen’s electron jump from n = 1 to– N = 2– N = 3– N = 4

Elements beyond Hydrogen

• Require different amounts of ionization energy (Graph shows outside electron)

• Top Right

Atom Size

• Large = More Lines

• Uranium on Bottom

• Hydrogen on Top

Molecules verse Atoms

• Would also have a much larger range of emission lines and spectra

• How many eV’s required for Helium’s 588nm emission? How many eV’s required for Heliums 402nm emission?

How much energy between shells?

• Follows (1/n2)

• If the n = 1 is equal to – 16 eV, how many eV of energy does a– N = 2 electron have?

• - 16 eV x (1/22) = - 4 eV– N = 4 electron have?

• How much energy is released going from N = 4 to N = 2? What wavelength is that?

Back to Waves

• Electron Cloud: Represents a high (90%) probability of finding an electron

• Quantum Mechanics: The Study of the properties of matter using its wave properties

• Coherent Light: When waves of light are in sync with one another, maxima and minima lining up

Lasers

• Create Coherent Light by Stimulated Emission

• An electron in an excited state hit by a photon will fall releasing light in phase with the light that hit it

Which is coherent?