Download CHM 1025 Chapter 9 web

Chapter 9
“Electrons in Atoms and the Periodic
Table”
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Blimps, Balloons, and Models for the
Atom
• Hindenburg
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Blimps, Balloons, and Models for the Atom
• Properties of
Elements
– Hydrogen Atoms
– Helium Atoms
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Blimps, Balloons, and Models for the Atom
• Periodic Law
– When elements are arranged in
order
of increasing
atomic number, certain sets of
properties recur periodically.
• Hydrogen
• Helium
• Why similarity?
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What we know about the atom?
• Rutherford concluded that the nucleus
contained protons. He could account for the
charge of the nucleus, but the mass of was
too large for the number of protons.
• Protons and neutrons make up most of the
mass of the atom and are in the nucleus.
• Electrons are very light and are flying
around outside the nucleus.
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How are the electrons arranged in
the atom?
• In order to understand how electrons are
arranged, we must know something about
electromagnetic radiation.
• Examples of electromagnetic radiation are:
___________________________________
________________
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Light and Electromagnetic
Radiation
• Observation: When certain elements are
heated or electronically excited, they emit
light of different colors. When the light is
separated into various colors by a
spectroscope, a spectrum is observed.
• Light is one type of electromagnetic
radiation.
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What does Light have to do with Atoms?
• When certain elements are
heated or electronically
excited, they emit light of
different colors.
• The light can be separated
into various colors by a
spectroscope, a line
spectrum is observed.
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Models for the Atom
• Model for Atomic Structure
– Based on Scientific Method
• Bohr Model
– Developed in early 1900s
– Niels Bohr
• Quantum Mechanical Model
– Developed in early 1900s
– Caused a revolution in the
Physical Sciences
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Light: Electromagnetic Radiation
• Electromagnetic Radiation
• Photon
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Light: Electromagnetic Radiation
• Wave–________________
• Wavelength
– Wave Nature of Light
– Distance between
Adjacent Wave Crests
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Wavelength of Light
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Light: Electromagnetic Radiation
• Color
– Determined by
Wavelength
– Visible Light
• What you can see
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Light: Electromagnetic Radiation
• Energy
– Wavelength determines Energy
– ______________________________
• Frequency
– Another Characterization
– Cycles per Second
– Wave Crest that pass per Second
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Light: Electromagnetic Radiation
• Summary - Electromagnetic Radiation
– Form of Energy
– Speed of light = 3.0 X 108 m/s
– Wavelength determines the Energy
– Shorter Wavelength – Higher the Energy
– Frequency has inverse relationship to
Wavelength
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The Bohr Model: Atoms with Orbits
• Atoms and Energy
– Absorbed Energy Re-emitted as
Light
– Atoms Emit Unique Spectra – Color
• Emission Spectrum
– Light Emitted by Glowing Elemental
Gas
– Elements have Unique Emission
Spectra
– Spectra Characteristic of Element
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The Bohr Model: Atoms with Orbits
• White Light Spectrum
– Continuous
• Emission Spectrum
– Bright Spots at
Specific Wavelengths
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The Bohr Model: Atoms with Orbits
• Emission Spectrum and the
Atomic Model
– Explanation of Bright Line
Spectra
– Unique Spectra for Each
Element
• Bohr Model
– Electrons Travel in Circular
Orbits
– Planetary Model
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The Bohr Model: Atoms with Orbits
• Bohr Model
– Specific Fixed Orbits
– Energy of each Orbit
Specified
• Quantum Numbers
– Specify Orbits
– Quantized Orbits
– Like Steps in a Ladder
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The Bohr Model: Atoms with Orbits
• Quantum Numbers
– Steps on Ladder
– Cannot Stand between
Steps
– Principal Quantum Number
• “n”
• Distance from the Nucleus
• Energy
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The Bohr Model: Atoms with Orbits
• Excitation of Electrons
– Absorbs Energy
– Promoted to “higher”
Energy Orbit
• Quantum of Energy
– Relaxes
– Emits a Photon
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The Bohr Model: Atoms with Orbits
• Quantum of Energy
– Relaxes
– Emits a Photon
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The Bohr Model: Atoms with Orbits
• Summary
– Electrons exist in Quantized Orbits
• Specific Fixed Energies
• Specific Fixed Distances
– Energy Excites Electron
• Electrons are Promoted to Higher Energy Orbits
– Atoms Emit Light
• Electrons fall from Higher Energy Orbits
– Energy and Wavelength
• Corresponds to the Difference in Energy between the Orbits
• Energies are Fixed and Discrete
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The Quantum Mechanical Model:
Atoms with Orbitals
• Orbitals
– Replace Circular Orbits
– Not Specific Path
– Statistical Distribution of Electron
• Probability Maps
– Show where Electron is “likely” to be Found
– Electrons Do Not Act like Particles
– Non-Intuitive
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Quantum Mechanical Model
Atoms with Orbitals
• Baseballs and Electrons
– Baseballs
• Trace the Baseball Path
• Predict where the Baseball
crosses Home Plate
– Electrons
• Impossible for Electron
• Wave–Particle Duality
• No Predictable Path
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The Quantum Mechanical Model:
Atoms with Orbitals
• Orbits to Orbitals
– Bohr Model
• Orbit
• Circular Path around the Nucleus
– Quantum Mechanical Model
• Orbital
• Probability Map
• Different Orbital Shapes
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Quantum Mechanical Orbitals
• Principal Quantum Number – n
– Identifies the Principal Shell of the orbital
– Higher Principal Quantum Number
denotes higher energy
• Subshell
– Indicated by Letter  s, p, d, or f
– Specifies Shape of Orbital
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Quantum Mechanical Orbitals
• “s” Subshell
– Spherical Shape
– 3-D Probability Map
– Dot Density is
proportional to
probability of finding
Electron in that area
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Quantum Mechanical Orbitals
• “n” = 2
– Two Subshells
– “s”
• Similar to 1s
• Larger
– Has a “p”
subshell
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Charge Cloud
Representations
of “s” Orbitals
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Quantum Mechanical Orbitals
• “p”
• Three
Orbitals
• Different
Orientations
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Shapes
of “p”
Orbitals
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Quantum Mechanical Orbitals
• Orbital Diagrams
– Similar Information
– Electrons as Arrows
• Pauli Exclusion Principle
• Electron Spin
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C
6 electrons
1s2 2s2 2p2
[He]2s22p2
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Quantum Mechanical Orbitals
• Orbitals Fill
to Minimize Energy
• 1s, 2s, 2p, 3s, 3p, 4s
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Ni
28 electrons
1s22s2 2p6 3s2 3p64s2 3d8
[Ar] 4s23d8
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Quantum Mechanical Orbitals
• Summary of Electrons and Orbitals
– Electrons Occupy Orbitals to Minimize
Energy
• Lower Energy Orbitals Fill First
• Aufbau Diagram gives Order
– Orbitals Hold 2 Electrons
• Pauli Exclusion Principle
• Opposing Spins
– Electrons Occupy Orbitals Singly First
• Hund’s Rule
• Parallel Spins
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Quantum Mechanical Orbitals
• Electron Configuration
– “s” Subshell
• 1 Orbital
• 2 Electrons
– “p” Subshell
• 3 Orbitals
• 6 Electrons
– “d” Subshell
• 5 Orbitals
• 10 Electrons
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Electron Configurations and the Periodic Table
• Valence Electrons
– Electrons in the Outermost
Principal Shell
– Electrons Involved in
Chemical Bonding
• Core Electrons
– Electrons Not in the
Outermost Principal Shell
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Valence Electrons
• The outer electrons in an atom are valence
electrons.
• Valence electrons can be represented with
dots in the Lewis electron dot symbol.
• Each outer electron is represented by a dot
around the atomic symbol:
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Electron Configurations and the Periodic Table
• Patterns in the Periodic Table
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Electron Configurations and the Periodic Table
• Electron Configurations in the Periodic Table
– Inner Electron Configuration is the Electron
Configuration of the Noble Gas that immediately
precedes that element in the Periodic Table.
– Outer Electrons can be deduced from the element’s
position within a particular block (s, p, d, and f).
– Highest Principal Quantum Number is equal to the
Row.
– For “d” electrons, the Principal Quantum Number of
the outermost “d” electrons is n – 1.
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Electron Configurations and the Periodic Table
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Insert figure 5.32
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Insert figure
5.33
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Quantum Mechanical Model
• Noble Gases
–
–
–
–
Group 8
Not Reactive
p6
Completely Full Valence Shell
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Quantum Mechanical Model
• Alkali Metals
– Group 1
– Reactive
– s1
– Ions lose 1 electron
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Quantum Mechanical Model
• Alkaline Earth Metals
–
–
–
–
Group 2
Reactive
s2
Ions lose 2 electrons
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Quantum Mechanical Model
• Halogens
–
–
–
–
Group 7
Reactive
p5
Ions gain 1 electron
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Periodic Trends: Ionization Energy
• Ionization Energy (IE)
– Energy required to remove an electron
from an atom in the gaseous state
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Periodic Trends: Ionization Energy
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Periodic Trends: Atomic Size
• Atomic Size (AS)
– Distance of outermost electrons from
the Nucleus
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Periodic Trends: Atomic Size
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Periodic Trends: Metallic Character
• Metallic Character (MC)
– Metals lose electrons
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Periodic Trends: Metallic Character
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