Download 4.1 The Development of a New Atomic Model • Properties of Light o

CHAPTER 4 OUTLINE/NOTES HONORS CHEMISTRY 2010 4.1 The Development of a New Atomic Model
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Properties of Light
o Wave Description of Light
ƒ Electromagnetic radiation
ƒ EM Spectrum
ƒ Wavelength and frequency
ƒ Visible spectrum (ROY G BIV)
ƒ c = λυ
Photoelectric Effect
o Particle Description of Light
ƒ Quantum
ƒ E = hυ
ƒ Photon
Hydrogen Atom Line Emission Spectra
ƒ Ground state vs., excited state
ƒ Line emission spectra
ƒ Continuous spectra
Bohr’s Model of an Atom
ƒ Planetary Model of an Atom
4.2 The Quantum Model of an Atom
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Electrons as Waves
Heisenberg Uncertainty Principle
Schrodinger Wave Equation
Atomic Orbitals and Quantum Numbers
o Quantum numbers (Q#)
o n, l, m, s
ƒ n = principle Q# (1, 2, 3, 4, 5 …)
ƒ l = sublevel or angular momentum Q# (0, 1, 2, 3)
ƒ m = orbital or magnetic Q#(…-2, -1, 0, 1, 2…)
ƒ s = spin Q# (1/2 or -1/2)
4.3 Electron Configurations
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Rules for Electron Configurations
o Aufbau principle
o Pauli exclusion principle
o Hund’s rule
Representing Electron Configurations
o Orbital Notation
o Electron Configuration Notation
o Elements of the Second Period
o Elements of the Third Period
ƒ Noble Gas Notation
o Elements of the Fourth Period
o Elements of the 5th, 6th and 7th Periods
CHAPTER 4 OUTLINE/NOTES HONORS CHEMISTRY 2010 4.1 – Properties of Light • The Nuclear Atom and Unanswered Questions o Although Rutherford’s scientific model of an atom was a breakthrough, it lacked detail about how electrons occupy the space surrounding the nucleus of an atom. o Questions Still Unanswered: • How are an atom’s electrons arranged in space around the nucleus? • Why aren’t negatively charged electrons pulled in towards the nucleus? • Why are there differences in chemical behavior among the various elements? o One scientist named Neils Bohr thought of electrons being in “orbit” around the nucleus in much the same manner as Earth is in orbit around the sun. This is sometimes called the planetary atomic model or Bohr’s Model. o So a hydrogen atom should be similar to a solar system consisting of a sun and one planet. CHAPTER 4 OUTLINE/NOTES HONORS CHEMISTRY 2010 o Scientists began to unravel the puzzle of chemical behavior in the early 1900’s and observed that certain elements emitted visible light when heated in a flame. o Analysis of the emitted light revealed that an elements chemical behavior is related to the arrangement of the electrons in its atoms. • Wave Nature of Light & Spectroscopy o When a substance is exposed to a certain intensity of light or some other form of energy, the atoms absorb some of that energy and are said to be in an “excited” state. o Spectroscopy is the study of the interaction of matter and radiant energy. It is a method of studying substances that are exposed to some sort of exciting energy. o Electromagnetic Radiation: A form of energy that exhibits wavelike behavior as it travels through space. • Types of electromagnetic radiation include waves ranging from very low to very high energy (a product of frequency). Visible light is a component of this spectrum in addition to CHAPTER 4 OUTLINE/NOTES HONORS CHEMISTRY 2010 radio waves, ultraviolet light, infrared light, x‐
rays, gamma rays. o Wavelength and Frequency • Wavelength (λ) a.k.a. lambda = the distance between two similar points on two successive waves. Measured in meters. • Amplitude = the height the crest or depth of the trough. Refers to the intensity or brightness of a light. • Frequency (ν) a.k.a. nu= the number of waves that pass a point per second. This is what changes the energy of a wave. Hertz (Hz) is a measure of frequency or cycles. We commonly use MHz or megahertz (1 MHz = 1 x 106 Hz). CHAPTER 4 OUTLINE/NOTES HONORS CHEMISTRY 2010 o Speed of Light Equation: c = λν • The product of frequency (in Hz or s‐1) and wavelength (in meters) is equal to the speed of light which is a constant. • Speed of Light: c = 3.00 x 108 m/s o Electromagnetic Spectrum • Copy Figure below: CHAPTER 4 OUTLINE/NOTES HONORS CHEMISTRY 2010 o Visible Light : ROYGBIV* • Red (lowest energy) • Orange • Yellow • Green • Blue • Indigo • Violet (highest energy) Wavelength and Frequency Practice Problems: What is the wavelength associated with the following frequencies: a) 9.10 x 1014Hz b) 106.1 MHz CHAPTER 4 OUTLINE/NOTES HONORS CHEMISTRY 2010 c) 93.9 MHz Find the frequencies associated with the following wavelengths: e) 6.25 x 10‐8m f) 456 nm g) 590 nm • Particle Nature of Light – The wave theory of light does not explain its everyday behavior and fails to adequately describe important aspects of lights interactions with matter. o Quantum Concept • Max Planck began searching for explanation for light emitted by heated objects and he found that matter can gain or lose energy only in small, specific amounts called quanta. o Energy of Light Equation: E = hv • E is energy measured in joules (J) • h is Planck’s constant and is equal to 6.626 x 10‐34 J.s • v is frequency in 1/s o Photoelectric Effect CHAPTER 4 OUTLINE/NOTES HONORS CHEMISTRY 2010 • The process by which electrons are ejected from a substance when light of a certain frequency shines on its surface. This type of technology is used in solar powered devices such as calculators Questions to keep in mind: • What types of waves are of the highest energy? of the lowest energy? CHAPTER 4 OUTLINE/NOTES HONORS CHEMISTRY 2010 • What wavelengths (long or short) are of low energy? of high energy? • What frequencies (big or small) are of low energy? of high energy? o Practice Problems #’s 5 and 6 Ground State vs. Excited State Normally, if an electron is in a state of lowest possible energy, it is in a ground state. If an electron gains energy, it moves to an excited state. An electron in an excited state will release a specific quantity of energy as it quickly “falls” back to its ground state. This energy is emitted at certain wavelengths of light, which give each element a unique line‐
emission spectrum. Spectra CHAPTER 4 OUTLINE/NOTES HONORS CHEMISTRY 2010 The spectrum of light released from excited atoms of an element is called the emission spectrum of that element. Emission Spectra of Hydrogen and Iron An absorption spectrum occurs when light passes through a cold, dilute gas and atoms in the gas absorb at characteristic frequencies; since the re‐emitted light is unlikely to be emitted in the same direction as the absorbed photon, this gives rise to dark lines (absence of light) in the spectrum. CHAPTER 4 OUTLINE/NOTES HONORS CHEMISTRY 2010 Bohr Model of the Atom According to his model, hydrogen’s atomic emission spectrum results from electrons dropping from higher‐
energy atomic orbits to lower‐energy atomic orbits. CHAPTER 4 OUTLINE/NOTES HONORS CHEMISTRY 2010 4.2 The Quantum Model of an Atom
• The Quantum Mechanical Model of the Atom
o We now need to look for ways to refine our model
of the atom
o Matter and energy are related and they share
properties of both particles and waves. This is called
Wave-Particle Duality.
o This model is based on the assumption that electrons
are waves.
o A French scientist named De Broglie that proposed a
hypothesis that particles can have some of the
properties of waves.
CHAPTER 4 OUTLINE/NOTES HONORS CHEMISTRY 2010 o He was able to predict the wavelength of a given
particle with m = mass and v = velocity.
o Scientists were able to show how an electron stream
acted in the same way as a ray of light.
o One cannot observe both the particle and wave
properties of an electron in the same experiment.
• The Heisenberg Uncertainty Principle
o A German scientist that found it was impossible to
know both the exact position and the exact
momentum (speed) of an electron at the same time.
You may only know one or the other at one time.
o In order for us to “see” an electron, a photon of light
must hit that electron and be reflected off it.
However, a collision between a photon and an
electron results in a large change in the energy of the
electron thus causing its velocity to change.
o And on the other hand, if we measure the electrons
velocity (speed) we will change its position in the
process.
o Uncertainty is related to Planck’s constant (h) and
momentum (p). The more certain we are of the
position of an electron, the less certain we are of its
momentum.
CHAPTER 4 OUTLINE/NOTES HONORS CHEMISTRY 2010 • Schrodinger’s Work
o Heisenberg’s work treated the electron as a particle
but what if we look at it as a wave instead?
o Schrodinger was an Austrian physicist who
developed a mathematical equation to describe the
wave-like behavior of an electron.
o He introduced the idea of four quantum numbers that
are used in describing electron behavior.
o A probability of the location of an electron in a
given position around the nucleus can be calculated
from his equation.
• Wave Mechanical View of Hydrogen Atom
o Using computers to calculate the probability of the
location of an electron, a three-dimensional shape
(model) is formed. The most probable place to find
an electron will be somewhere on the surface of this
calculated 3-D shape.
CHAPTER 4 OUTLINE/NOTES HONORS CHEMISTRY 2010 o This 3-D shape is called an electron cloud. Note
analogy between fan blades and an electron cloud
• Atomic Orbitals and Quantum Numbers o Electrons occupy three‐dimensional regions of space called atomic orbitals. o Schrodinger’s Wave equation can predict the probable location of the electrons in an atom. o There are 4 orbital types based on energy sublevel: • s – sphere shaped, 1 per sublevel • p – lobe shaped, 3 per sublevel • d – complex shaped, 5 per sublevel • f – most complex shaped, 7 per sublevel CHAPTER 4 OUTLINE/NOTES HONORS CHEMISTRY 2010 • Quantum Numbers: o n = principle energy level (1‐7) o l = sublevel (s, p, d and f) o m = orbital (2 e‐ max per orbital and shape related to sublevel) o s = spin (up or down) CHAPTER 4 OUTLINE/NOTES HONORS CHEMISTRY 2010 4.3 – Electron Configurations • Ground State Electron Configurations o Aufbau Principle – electrons fill lowest energy levels first. o Pauli Exclusion Principle – only 2 electrons can occupy an orbital and must have opposite spins (means they move in opposite directions) o Hund’s Rule – electrons fill the orbitals of an energy level with the same spin first then the opposite spin. • Orbital Filling Diagrams and Electron Configurations Filling sequence: CHAPTER 4 OUTLINE/NOTES HONORS CHEMISTRY 2010 s sublevel ‐ 1 orbital – 2 e‐ max p sublevel – 3 orbitals – 6 e‐ max d sublevel – 5 orbitals – 10 e‐ max f sublevel – 7 orbitals – 14 e‐ max CHAPTER 4 OUTLINE/NOTES HONORS CHEMISTRY 2010 • Practice Problems: o Pg 139 #’s 18‐22 CHAPTER 4 OUTLINE/NOTES HONORS CHEMISTRY 2010 Valence Electrons and Lewis Dot Structures o The outer most electrons (highest energy level, s and p orbitals only) of an atom are called the valence electrons. These are the electrons involved in chemical reactions. o It is often useful to draw these outer electrons around the symbol of an element. This notation is called a Lewis Electron Dot Diagram.