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SUMMARY
Electrons in Atoms
(Section 29.1) The Bohr model fails to fully describe atoms because
it combines elements of classical physics with some principles of
quantum mechanics. To explain the observed properties of an
atom, electrons must be described with a wave function that is
determined by solving the Schrödinger equation. As a result, some
properties of the atom are quantized, including orbital and spin
angular momentum. The quantum numbers 1 n, l, ml , s 2 specify
the quantum-mechanical states of the atom, and according to the
Pauli exclusion principle, no two electrons in an atom can occupy
the same state.
0C02
0C02
1s
r
0
2s
r
0
2s
1s
r
r
Atomic Structure
(Section 29.2) We can imagine constructing a neutral atom by starting with a bare nucleus with Z protons and adding Z electrons, one
by one, respecting the Pauli exclusion principle. To obtain the
ground state, we fill the lowest-energy states (those closest to the
nucleus, with the smallest values of n and l) first, and we use successively higher states until all the electrons are in place. By filling
the atomic states we begin to learn the chemical properties of
atoms, which are determined principally by interactions involving
the outermost electrons.
Nucleus: 13e
1s subshell: 22e
2s subshell: 2e
Diatomic Molecules
(Section 29.3) An ionic bond is a bond between two ionized atoms—
one atom gives at least one electron to fill a vacancy in the shell of
the other. In a covalent bond, the electron cloud tends to concentrate between the atoms—the positive nucleus of each atom is
attracted to the somewhat centralized electron cloud. There are also
weaker bonds such as the van der Waals and hydrogen bonds.
Covalent bond
H2
Structure and Properties of Solids
(Section 29.4) A crystalline solid is characterized by long-range
order, a recurring pattern of atomic positions that extends over
many atoms. Liquids have short-range order. We can understand
many macroscopic properties of solids, including mechanical,
thermal, electrical, magnetic, and optical properties, by considering their relation to the microscopic structure of the material.
Face-centered
cubic
Semiconductors
(Sections 29.5–29.7) A semiconductor is a material with an electrical
resistivity that is intermediate between those of good conductors
and those of good insulators. A hole is a vacancy in a bond where
there would normally be an electron— the hole acts like a positive
charge. In n-type semiconductors, the conductivity is due to the
motion of electrons; in p-type, holes act as the moving charges.
A transistor can be made by layering two p-n junctions—the
resulting devices can act as power, current, or voltage amplifiers.
Superconductivity
(Section 29.8) As the temperature decreases in a superconductor, the
resistivity at first decreases smoothly. But then at the critical temperature, a phase transition occurs and the resistivity suddenly
drops to zero. One recently discovered superconductor has a a critical temperature of 160 K. When we place a superconductor in a
magnetic field, eddy currents are induced that exactly cancel the
applied field everywhere inside the material—a magnetic field can
never exist inside a type-I superconducting material.
Conduction electron
–
Eg
E
–
Hole
Band gap
–
+
–
+
–
–
–
–
–
–
S
E
Conduction band
Valence band
Body-centered
cubic