Download Louisiana Tech University, Chemistry 281

GHW#3. Chapter 3. Louisiana Tech University, Chemistry 481. POGIL(Process
Oriented Guided Inquiry Learning) Exercise on Chapter 3. Electronic Structure of
Sloids.
Why?
Metals
How is metallic bond different from covalent and ionic bond? How metals were discovered and
affected the development of civilization? What is metallurgy? How are metals extracted from ores?
What are metallic properties? What bonding models are used to explain metallic bond? What is electronsea model of metallic bonding? How was molecular orbital theory (MO) based on LCAO (called band
theory) is used to explain metallic bonding? What is the difference between a conductor, insulator, and
semiconductor. What are valence band, conduction band and band gap? What is the difference between
thermal/photo (Intrinsic) semiconductivity and doped (Extrinsic) semiconductivity? How is a p-type
semiconductor and n-type semiconductor is created by doping? How the semiconductors did
revolutionized electronic industry? What is a transistor and integrated circuit?
Instructional Objectives
The student s understands the:
 The difference between metallic bond, covalent and ionic bond.
 Discovery of metals and importance to the development of civilization.
 Metallic properties and explain them using metallic bonding models.
 Band theory based on molecular orbital theory (MO) based and LCAO.
 The differences between a conductor, insulator, and semiconductor.
 The valence band, conduction band and band gap.
 Difference between intrinsic and and extrinsic semiconductivity.
 The difference between a p-type semiconductor and n-type semiconductor.
 The importance of semiconductors to electronic industry.
Success Criteria
Ability to answer the questions and apply concepts related to the topics given in the instructional
objectives.
RESOURCES
INORGANIC CHEMISTRY By Peter Atkins, Tina Overton, Jon Rourke, Mark Weller,
Fraser Armstrong, 4th Edition 2006.
New Concepts
Metals
Currently there are 86 known metals. Metals of Antiquity, were the metals upon which civilization was
based and there are seven: Au, Cu, Ag, Pb, Sn, Fe and Hg. Then Pt, Sb, Bi, Zn and As were discovered.
Earlier metals were extracted by smelting, by reduction with carbon and hydrogen, electroplating.
Metallurgy the study of the physical and chemical behavior of metallic elements and their mixtures,
alloys developed into a specific scientific discipline.
Metallic Properties
a) Good conductors of heat and electricity
b) Metallic luster
c) Malleable and ductile in their solid state
d) Have one to four valence electrons.
e) Low ionization potentials; they readily lose electrons.
f) Good reducing agents.
g) Have hydroxides which are bases or amphoteric.
h) Electropositive.
Metallic Bonding Models
The difference in chemical properties between metals and non-metals lie mainly in the fact those atoms
of metals fewer valence electrons and they are shared among all the atoms in the substance: metallic
bonding.
a) Electron-sea model of bonding
The metallic bond consists of a series of metals atoms that have all donated their valence electrons to an
electron cloud, referred to as an electron sea which permeates the entire solid. It is like a box (solid) of
marbles (positively charged metal cores: known as Kernels) that are surrounded by water (valence
electrons).
 Metallic bond together is the attraction between the positive kernels and the delocalized negative
electron cloud.
 Fluid electrons that can carry a charge and kinetic energy flow easily through the solid making
metals good electrical and thermal conductor.
 The kernels can be pushed anywhere within the solid and the electrons will follow them, giving
metals flexibility: malleability and ductility.
b) Molecular orbital theory
Molecular Orbital Theory applied to metallic bonding is known
as Band
Theory. Band theory uses the LCAO of all valence atomic
orbitals of
metals in the solid to form bands of s, p, d, f bands (molecular
orbitals) just
like simple molecular orbital theory is applied to a diatomic
molecule,
hydrogen(H2).
Types of conducting materials
a) Conductor (which is usually a metal) is a solid with a partially full band.
b) Insulator is a solid with a full band and a large band gap.
Valence band: The highest filled band of MOs
Conduction band: The lowest unfilled band of MOs
Band Gap: The energy separation between the top of the valence band and the bottom of the
conduction band.
c) Semiconductor is a solid with a full band and a small band gap.
Semiconductivity
Thermal/photo (Intrinsic) semiconductivity: Small conductivity created by the thermal/photo
excitations electrons from valence to conduction bands.
Doped (Extrinsic) semiconductivity:
Small conductivity created by a doping through loss/gain of electrons from valence/conduction bands,
respectively.
a) p-type semiconductor: Positive holes created in the insulator by an electron poor dopent.
b) n-type semiconductor: Electron holes created in the insulator by a electron rich dopent.
Diode: Diodes allow electricity to flow in only one direction. The arrow of the circuit symbol shows the
direction in which the current can flow.
Transistor: Has three terminals where, an application of voltage to the input terminal increases the
conductivity between the other two terminals and hence controls current flow through those terminals
for amplification, switching, voltage stabilization, signal modulation and many other functions.
Chapter 4. Metallic bonding
GHW# 3. Chapter 3. Key Questions (relatively simple to answer using the Focus Information)
1. Describe the importance of metals in the development of civilization.
2. What are the properties of metals that distinguish them from non-metals?
3. What is metallurgy?
4. Describe metallic bonding and properties in terms of:
a) Electron-sea model of bonding:
b) Band Theory:
5. Draw the s band (molecular orbitals) for ten Na on a line (one dimentional) and show bonding
and anti-bonding molecular orbitals and fill electrons.
6. Describe the metallic properties of sodium in terms of band theory.
7. Using a band diagram, explain how magnesium can exhibit metallic behavior even though its 3s
band is completely full.
8. Draw a Band diagram for carbon/silicon/germanium/tin, and label valence band, conduction
band and band gap?
9. Draw a band diagrams to show the difference between(Band gaps: C = 5.47, Si = 1.12, Ge
= 0.66, Sn = 0)
a) Conductor (Sn):
b) Insulator (C):
c) Semiconductor (Ge):
10. Draw a band diagram for thermal/photo (Intrinsic) and doped (Extrinsic) semiconductors and
explain the origin of semicondictivity?
a) Thermal/photo (Intrinsic) (Ge):
b) Doped (Extrinsic) (Si/As):
11. Draw a band diagram for a p-type (Si/Ga) and n-type (Si/As) semiconductors and show holes
and electrons that is responsible for semiconductivity.
a) p-type(Si/Ga):
b) n-type(Si/As):
12. What is a transistor with emitter (E), collector(C) and base (B),
and how it works?
13. What the difference between a transistor (semiconductor device) and vacuum tube?
14. Using the diagram explain how a diode work.
15. What is an integrated circuit?