 Unit 4 The Arrangement of Electrons Ch. 4

Exam 4 Analysis  Averages  The Atom+/25(%)  Measurement+/15(%) up from %  Phases/KMT+/10(82%) down from % **Plan of Action!**

What Do You Think? Electron Placement Describe the location of electrons in a single lithium (Li) atom.

The Development of a New Atomic Model  Ernest Rutherford  Model incomplete did not describe why the electrons where not pulled to the center of the atom (positively charged nucleus), opposite charges attract.  Early Twentieth Century – New/Revised Atomic Model  Absorption and Emission of light by matter  Relationship between light and an atom’s electrons  Light behaves like a particle and a wave. (Particle-wave duality)  Particle-Wave Duality 1 Particle-Wave Duality 1  Particle-Wave Duality 2 Particle-Wave Duality 2

Electromagnetic Radiation  A form of energy that exhibits wavelike behavior as it travels through space.  Gamma Rays, X-rays, Ultraviolet, Infrared, Microwaves, Radio waves.  Electromagnetic Spectrum  All types of light waves move at a constant speed (3.0 x 10 8 m/s – “the speed of light”) through a vacuum (relatively the same for air)  Speed = Wavelength x Frequency c = λν  Wavelength – distance between corresponding points on adjacent waves (meters).  Frequency – number of waves that pass a given point in a specific time.

Photoelectric Effect  Emission of electrons from a metal when light shines on the metal  Electromagnetic radiation (light) strikes the surface of the metal ejecting electrons from the metal and causing an electric current, if the frequency was below a certain minimum.

The Particle Description of Light  Quantum  The minimum quantity of energy that can be lost or gained by an atom.  Photon  A particle of electromagnetic radiation having zero mass and carrying a quantum of energy.

Check for Understanding  What is the difference between the excited and ground state?  List the different types of electromagnetic radiation found in the electromagnetic spectrum.  How are frequency, wavelength, and energy related?

The Hydrogen-Atom Line-Emission Spectrum  Ground State  Lowest energy state of an atom  Excited State  An atom has higher potential energy than it has in its ground state  When returning to ground state, the atom gives off the energy it gained in the form of electromagnetic radiation (light)  Video Video  Line-Emission Spectrum  When a narrow beam of emitted light is shined through a prism, it then is separated into four specific color(s) of the visible spectrum.

Bohr Model of the Hydrogen Atom  Niels Bohr  Proposed a hydrogen-atom model that linked the atom’s electron to photon emission  The electron can circle the nucleus only in allowed paths called ORBITS  Absorption  Energy must be added to an atom in order to move an electron form a lower energy level to a higher energy level.  Emission  When the electron falls to a lower energy level  A photon is emitted (light)

The Quantum Model of the Atom  The Heisenberg Uncertainty Principle  States that it is impossible to determine simultaneously both the position and velocity of an electron or any other particle.  One of the fundamental principles of our present understanding of light and matter.

The Quantum Model of the Atom  The Schrodinger Wave Equation  Hypothesis that electrons have a dual wave-particle nature  Helped lay the foundation for Modern Quantum Theory  Describes mathematically the wave properties of electrons and other very small particles.  Gives only the probability of finding electrons at a given place around the nucleus  Electrons do not travel in neat orbits, now in regions called orbitals  3-D region around the nucleus that indicates the probable location of an electron  Different shapes and sizes

Flame Test Lab  See hand-out.  7 Stations  15 minutes to complete

Emission Spectra  Bulbs (H, He, Ne, Ar, and N) and Emission Spectra. “The relationship between electrons and energy is The emission spectra is produced by......”

Electron Orbital -Electrons orbit the nucleus in orbital clouds. -Electrons with different amounts of energy exist in different energy levels.

The Electron Cloud Model

Electrons in each energy level Each energy level can hold a limited number of electrons. The lowest energy level is the smallest and the closest to the nucleus.

Electron Orbital Continued Energy Level# of Electrons

Draw the Atoms Lithium Atom: 3 Protons 3 Neutrons 3 Electrons Aluminum Atom: 13 Protons 13 Neutrons 13 Electrons

Valence Electrons The electrons in the outermost energy level are called valence electrons. See Periodic Table

- Complete in YOUR notes!  Determine the number of protons, neutrons, electrons AND draw the Bohr models of the following atoms: A. Gallium B. Krypton C. Sulfur D. Titanium

For Next Time…  Complete Part 1 Formative in first 5 minutes of class!  Read pages !!