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