Post on 21-Dec-2015
Chemistry for Changing Times12th Edition
Hill and Kolb
Chapter 3Atomic Structure:
Images of the Invisible
John SingerJackson Community College, Jackson, MI
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Electricity and the Atom
Electrolyte: A compound that conducts electricity when molten or dissolved in water.
Electrodes: Carbon rods of metallic strips that carry electrical current.
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E
Anode: A positive electrode.
Cathode: A negative electrode.
Electrolysis
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Ions
Ion: An atom or group of atoms with a charge.
Anion: A negative ion.
Cation: A positive ion.
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Cathode Ray Tubes
Mid-1800s: Crookes’ tube
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Thomson Experiment1897, Joseph John Thomson:
Determined the charge:mass ratio of cathode rays (discovered electrons).
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Goldstein’s Experiment: Positive Particles
1886, Goldstein: Observed positive rays using a perforated cathode.
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Electron Charge1909, Robert Millikan:
Using the oil-drop experiment, Millikan discovered the charge of an electron.
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X-Rays
1895, Wilhem Roentgen:
Using a cathode ray tube, Roentgen discovered X-rays.
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Radioactivity1895, Antoine Becquerel:
Discovered radioactivity.
Marie Curie and husband Pierre characterized radioactivity.
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Three Types of Radioactivity
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Three Types of Radioactivity
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Rutherford Gold Foil ExperimentUsing an apparatus similar to that shown below, Ernest Rutherford discovered the atomic nucleus.
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Rutherford Gold Foil Experiment
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Subatomic Particles
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Atomic Structure
Atomic number: The number of protons in a nucleus.
Mass number: The sum of protons and neutrons in a nucleus.
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IsotopesIsotopes have the same atomic number, but have different mass numbers (same number of protons, but different number of neutrons).
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Nuclear Symbol
Z
X
A
X = Element symbol
A = Atomic number
Z = Mass number
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Electron Arrangement:The Bohr Model
Flame tests: Different elements give different colors to a flame.
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Electron Arrangement:The Bohr Model
Continuous spectra: When light emitted from a solid substance is passed through a prism, it produces a continuous spectrum of colors.
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Electron Arrangement:The Bohr Model
Line spectra: When light from a gaseous substance is passed through a prism, it produces a line spectrum.
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Electron Arrangement:The Bohr Model
Quantum: A tiny unit of energy produced or absorbed when an electron makes a transition from one energy level to another.
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Electron Arrangement:The Bohr Model
When electrons are in the lowest energy state, they are said to be in the ground state.
When a flame or other source of energy is absorbed by the electrons, they are promoted to a higher energy state (excited state).
When an electron in an excited state returns to a lower energy state, it emits a photon of energy, which may be observed as light.
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Electron Arrangement
Energy states or levels are sometimes called shells.
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Electron Arrangement:The Quantum Model
The Quantum model of the atom is a probability-based model. It is composed of principle energy levels, sublevels, and orbitals.
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Electron Arrangement:The Quantum Model
Principle energy levels (shells): Roughly correlate to the distance that an electron is from an atom’s nucleus.
Sublevels (subshells): Each principle energy level (n) is divided into n sublevels.
Orbitals: Orbitals are a region in space representing a high probability of locating an electron. Each sublevel has one or more orbital.
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Electron Arrangement:The Quantum Model
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Electron Arrangement:The Quantum Model
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Electron Arrangement:The Quantum Model
Electron configurations: Allow us to represent the arrangement of the electrons in an atom.
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Electron Arrangement:The Quantum Model
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Electron Arrangement:The Quantum Model
The order-of-filling chart:
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Electron Arrangement:The Quantum Model
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Electron Configurations and the Periodic Table
The periodic table is considered by many to be the most predictive tool in all of chemistry.
It is composed of vertical columns called groups or families and horizontal rows called periods.
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Electron Configurations and the Periodic Table
Groups (families): Vertical columns in the periodic table. Groups contain elements with similar chemical properties.
Periods: Horizontal rows in the periodic table. Elements in a period demonstrate a range of properties from metallic (on the left) to nonmetallic (on the right).
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Electron Configurations and the Periodic Table
Valence electrons: • Valence electrons are the electrons in the
outermost principle energy level of an atom.
• These are the electrons that are gained, lost, or shared in a chemical reaction.
• Elements in a group or family have the same number of valence electrons.
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Electron Configurations and the Periodic Table
Some groups in the periodic table have special names:
• Alkali Metals: Group 1A – Valence electron configuration: ns1
• Alkaline Earth Metals: Group 2A– Valence electron configuration: ns2
• Halogens: Group 7A– Valence electron configuration: ns2np5
• Noble Gases: Group 8A– Valence electron configuration: ns2np6
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Electron Configurations and the Periodic Table
• Metals, Nonmetals, and Metalloids:– Metals
• Metallic luster, conduct heat and electricity, malleable, and ductile. Examples are sodium and copper.
– Nonmetals• Dull luster, nonconductors, and brittle. Examples are sulfur and bromine.
– Metalloids• Demonstrate properties of both metals and
nonmetals. Examples are silicon and arsenic.
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Electron Configurations and the Periodic Table