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Chapter 9 “Electrons in Atoms and the Periodic Table” C. Gambino Blimps, Balloons, and Models for the Atom • Hindenburg C. Gambino Blimps, Balloons, and Models for the Atom • Properties of Elements – Hydrogen Atoms – Helium Atoms C. Gambino 1 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? C. Gambino 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. C. Gambino 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: ___________________________________ ________________ C. Gambino 2 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. C. Gambino 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. C. Gambino 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 C. Gambino 3 Light: Electromagnetic Radiation • Electromagnetic Radiation • Photon C. Gambino Light: Electromagnetic Radiation • Wave–________________ • Wavelength – Wave Nature of Light – Distance between Adjacent Wave Crests C. Gambino Wavelength of Light C. Gambino 4 Light: Electromagnetic Radiation • Color – Determined by Wavelength – Visible Light • What you can see C. Gambino Light: Electromagnetic Radiation • Energy – Wavelength determines Energy – ______________________________ • Frequency – Another Characterization – Cycles per Second – Wave Crest that pass per Second C. Gambino 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 C. Gambino 5 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 C. Gambino The Bohr Model: Atoms with Orbits • White Light Spectrum – Continuous • Emission Spectrum – Bright Spots at Specific Wavelengths C. Gambino 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 C. Gambino 6 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 C. Gambino The Bohr Model: Atoms with Orbits • Quantum Numbers – Steps on Ladder – Cannot Stand between Steps – Principal Quantum Number • “n” • Distance from the Nucleus • Energy C. Gambino The Bohr Model: Atoms with Orbits • Excitation of Electrons – Absorbs Energy – Promoted to “higher” Energy Orbit • Quantum of Energy – Relaxes – Emits a Photon C. Gambino 7 The Bohr Model: Atoms with Orbits • Quantum of Energy – Relaxes – Emits a Photon C. Gambino 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 C. Gambino 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 C. Gambino 8 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 C. Gambino 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 C. Gambino 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 C. Gambino 9 Quantum Mechanical Orbitals • “s” Subshell – Spherical Shape – 3-D Probability Map – Dot Density is proportional to probability of finding Electron in that area C. Gambino Quantum Mechanical Orbitals • “n” = 2 – Two Subshells – “s” • Similar to 1s • Larger – Has a “p” subshell C. Gambino Charge Cloud Representations of “s” Orbitals C. Gambino 10 Quantum Mechanical Orbitals • “p” • Three Orbitals • Different Orientations C. Gambino Shapes of “p” Orbitals C. Gambino Quantum Mechanical Orbitals • Orbital Diagrams – Similar Information – Electrons as Arrows • Pauli Exclusion Principle • Electron Spin C. Gambino 11 C 6 electrons 1s2 2s2 2p2 [He]2s22p2 C. Gambino Quantum Mechanical Orbitals • Orbitals Fill to Minimize Energy • 1s, 2s, 2p, 3s, 3p, 4s C. Gambino Ni 28 electrons 1s22s2 2p6 3s2 3p64s2 3d8 [Ar] 4s23d8 C. Gambino 12 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 C. Gambino Quantum Mechanical Orbitals • Electron Configuration – “s” Subshell • 1 Orbital • 2 Electrons – “p” Subshell • 3 Orbitals • 6 Electrons – “d” Subshell • 5 Orbitals • 10 Electrons C. Gambino 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 C. Gambino 13 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: C. Gambino Electron Configurations and the Periodic Table • Patterns in the Periodic Table C. Gambino 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. C. Gambino 14 Electron Configurations and the Periodic Table C. Gambino Insert figure 5.32 C. Gambino Insert figure 5.33 C. Gambino 15 Quantum Mechanical Model • Noble Gases – – – – Group 8 Not Reactive p6 Completely Full Valence Shell C. Gambino Quantum Mechanical Model • Alkali Metals – Group 1 – Reactive – s1 – Ions lose 1 electron C. Gambino Quantum Mechanical Model • Alkaline Earth Metals – – – – Group 2 Reactive s2 Ions lose 2 electrons C. Gambino 16 Quantum Mechanical Model • Halogens – – – – Group 7 Reactive p5 Ions gain 1 electron C. Gambino Periodic Trends: Ionization Energy • Ionization Energy (IE) – Energy required to remove an electron from an atom in the gaseous state C. Gambino Periodic Trends: Ionization Energy C. Gambino 17 Periodic Trends: Atomic Size • Atomic Size (AS) – Distance of outermost electrons from the Nucleus C. Gambino Periodic Trends: Atomic Size C. Gambino Periodic Trends: Metallic Character • Metallic Character (MC) – Metals lose electrons C. Gambino 18 Periodic Trends: Metallic Character C. Gambino C. Gambino 19