Chapter 9. Blimps, Balloons, and Models for the Atom. Electrons in Atoms and the Periodic Table. Hindenburg. Properties of Elements Hydrogen Atoms

Transcription

1 Chapter 9 Electrons in Atoms and the Periodic Table Blimps, Balloons, and Models for the Atom Hindenburg Blimps, Balloons, and Models for the Atom Properties of Elements Hydrogen Atoms Helium Atoms 1

2 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? 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. 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: 2

3 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. 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. 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 3

4 Light: Electromagnetic Radiation Electromagnetic Radiation Photon Light: Electromagnetic Radiation Wave Wavelength Wave Nature of Light Distance between Adjacent Wave Crests Wavelength of Light 4

5 Light: Electromagnetic Radiation Color Determined by Wavelength Visible Light What you can see Light: Electromagnetic Radiation Energy Wavelength determines Energy Frequency Another Characterization Cycles per Second Wave Crest that pass per Second Light: Electromagnetic Radiation Summary - Electromagnetic Radiation Form of Energy Speed of light = 3.0 X 10 8 m/s Wavelength determines the Energy Shorter Wavelength Higher the Energy Frequency has inverse relationship to Wavelength 5

6 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 The Bohr Model: Atoms with Orbits White Light Spectrum Continuous Emission Spectrum Bright Spots at Specific Wavelengths 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 6

7 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 The Bohr Model: Atoms with Orbits Quantum Numbers Steps on Ladder Cannot Stand between Steps Principal Quantum Number n Distance from the Nucleus Energy The Bohr Model: Atoms with Orbits Excitation of Electrons Absorbs Energy Promoted to higher Energy Orbit Quantum of Energy Relaxes Emits a Photon 7

8 The Bohr Model: Atoms with Orbits Quantum of Energy Relaxes Emits a Photon 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 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 8

9 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 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 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 9

10 Quantum Mechanical Orbitals s Subshell Spherical Shape 3-D Probability Map Dot Density is proportional to probability of finding Electron in that area Quantum Mechanical Orbitals n = 2 Two Subshells s Similar to 1s Larger Has a p subshell Charge Cloud Representations of s Orbitals 10

11 Quantum Mechanical Orbitals p Three Orbitals Different Orientations Shapes of p Orbitals Quantum Mechanical Orbitals Orbital Diagrams Similar Information Electrons as Arrows Pauli Exclusion Principle Electron Spin 11

12 C 6 electrons 1s 2 2s 2 2p 2 [He]2s 2 2p 2 Quantum Mechanical Orbitals Orbitals Fill to Minimize Energy 1s, 2s, 2p, 3s, 3p, 4s Ni 28 electrons 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 8 [Ar] 4s 2 3d 8 12

13 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 Quantum Mechanical Orbitals Electron Configuration s Subshell 1 Orbital 2 Electrons p Subshell 3 Orbitals 6 Electrons d Subshell 5 Orbitals 10 Electrons 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 13

14 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: Electron Configurations and the Periodic Table Patterns in the Periodic Table 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. 14

15 Electron Configurations and the Periodic Table Insert figure 5.32 Insert figure

16 Quantum Mechanical Model Noble Gases Group 8 Not Reactive p 6 Completely Full Valence Shell Quantum Mechanical Model Alkali Metals Group 1 Reactive s 1 Ions lose 1 electron Quantum Mechanical Model Alkaline Earth Metals Group 2 Reactive s 2 Ions lose 2 electrons 16

17 Quantum Mechanical Model Halogens Group 7 Reactive p 5 Ions gain 1 electron Periodic Trends: Ionization Energy Ionization Energy (IE) Energy required to remove an electron from an atom in the gaseous state Periodic Trends: Ionization Energy 17

18 Periodic Trends: Atomic Size Atomic Size (AS) Distance of outermost electrons from the Nucleus Periodic Trends: Atomic Size Periodic Trends: Metallic Character Metallic Character (MC) Metals lose electrons 18

19 Periodic Trends: Metallic Character 19