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Chapter 9
“Electrons in Atoms and the PeriodicTable”
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Blimps, Balloons, and Models for theAtom
• Hindenburg
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Blimps, Balloons, and Models for the Atom
• Properties ofElements– Hydrogen Atoms
– Helium Atoms
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Blimps, Balloons, and Models for the Atom
• Periodic Law– When elements are arranged in
order of increasingatomic number, certain sets ofproperties recur periodically.
• Hydrogen
• Helium
• Why similarity?
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What we know about the atom?
• Rutherford concluded that the nucleuscontained protons. He could account for thecharge of the nucleus, but the mass of wastoo large for the number of protons.
• Protons and neutrons make up most of themass of the atom and are in the nucleus.
• Electrons are very light and are flyingaround outside the nucleus.
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How are the electrons arranged inthe atom?
• In order to understand how electrons arearranged, we must know something aboutelectromagnetic radiation.
• Examples of electromagnetic radiation are:___________________________________________________
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Light and ElectromagneticRadiation
• Observation: When certain elements areheated or electronically excited, they emitlight of different colors. When the light isseparated into various colors by aspectroscope, a spectrum is observed.
• Light is one type of electromagneticradiation.
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• When certain elements areheated or electronicallyexcited, they emit light ofdifferent colors.
• The light can be separatedinto various colors by aspectroscope, a linespectrum is observed.
What does Light have to do with Atoms?
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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 theAtomic Model– Explanation of Bright Line
Spectra– Unique Spectra for Each
Element• Bohr Model
– Electrons Travel in CircularOrbits
– 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 ModelAtoms 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 toprobability of findingElectron 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 CloudRepresentationsof “s” Orbitals
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Quantum Mechanical Orbitals
• “p”• Three
Orbitals• Different
Orientations
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Shapesof “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
1s22s22p2
[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
1s22s22p6 3s23p64s23d8
[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 theOutermost Principal Shell
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Valence Electrons
• The outer electrons in an atom are valenceelectrons.
• Valence electrons can be represented withdots in the Lewis electron dot symbol.
• Each outer electron is represented by a dotaround 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 immediatelyprecedes that element in the Periodic Table.
– Outer Electrons can be deduced from the element’sposition within a particular block (s, p, d, and f).
– Highest Principal Quantum Number is equal to theRow.
– For “d” electrons, the Principal Quantum Number ofthe 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 figure5.33
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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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