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Chemistry for Changing Times
12th Edition
Hill and Kolb
Chapter 3
Atomic Structure:
Images of the Invisible
John Singer
Jackson 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
Electrolysis
Anode: A positive
electrode.
Cathode: A negative
electrode.
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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 Experiment
1897, 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 Charge
1909, 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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Radioactivity
1895, 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 Experiment
Using 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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Isotopes
Isotopes 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
A
X
Z
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
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