Transcript Bonding in Solids

Bonding in Solids
Sovay, Jen and Miranda
Overview
• Physical properties of crystaline
solids, such as melting point
and hardness depend on the
arrangements of particles and
on the attractive forces
between them
Molecular Solids
• Molecular solids consist of atoms or
molecules held together by
intermolecular forces
• Intermolecular forces
• Dipole: dipole forces, london dispersion
forces, and hydrogen bonds
• Because forces are weak, Molecular
solids are soft
Properties of Molecular
Forces
• Depend on strengths of the
forces that exist between
molecules
• (Intermolecular forces that
depend on close contact are not
as effective, the melting pt is
lower)
Covalent-Network Solids
• -Consist of atoms held together
by covalent bonds
• -stronger than intermolecular
forces
• -these solids have higher
melting points and are harder
than molecular forces
Ionic Solids
• -Ions held together by ionic
bonds
• -Strength depends on charges of
ions
• -Structure can be classified as
few basic types
Basic Types of Ionic
Structures
• NaCl, HF, KCl, AgCl, and CaO
• For Na : each cation is surrounded by it’s six
neighboring anions because the Na ions have a
coordination number of 6
• CsCl - Each Cs ion is surrounded by eight
CL, Coordination # is 8 for CS
• Difference in coordination number is accounted for
by the larger size of Cs
• ZnS – Each of the small Zinc ions are
tetrahedrally surrounded by four S ions
(face centered cubic)
• CaF2, BaCl2, PbF2 – (face centered cubic)
all have twice as many anions as cations
Metallic Solids
• -Consist entirely of metal
atoms
• -Has several structures
• - Bonding too strong to be
due to London Dispersion
• Not enough valence e- to be
due to ordinary covalent
bonds
Metallic Solids
(continued)
• Bonding is due to valence
electrons that are delocalized
throughout the entire solid
• Vary greatly in bonding strength
• Mobility of electrons
Molecular Solids
Bonding Energy
•
•
•
•
Dispersion – 1.0 KJ/mole
Hydrogen Bond – 12-16 KJ/mole
Ionic – 50-100 KJ/mole
Covalent – 100-1000 KJ/mole
http://www.mikeblabber.org/oldwine/chm1045/notes/f
orces/Bonding
http://csma31.csm.jmu.edu/chemistry/augustine/gsci101/Topi
cs/Bonding_In_Solids/primary_bonding_summary.pdf
Bonding in Solids Cheat Sheet
Type of
Crystal
Forces
holding
units
together
General
Properties
Examples
Molecular
Inter molecular
forces
Soft, low melting
point, poor conductor
of heat and electricity
Ar, CO2, I1,
H2O,
C12H22O11
Ionic
Ionic
bonds
Hard, brittle, high
melting point, poor
conductor of heat and
electricity
NaCl, LiF,
MgO, CaCO3
Covalent
Covalent
bonds
Hard, high melting
point, poor conductor
of heat and electricity
C (diamond
or graphite)
Si, SiO2
Metallic
Metallic
bonds
Soft to hard, low to
high melting point,
good conductor of
heat and electricity
All metallic
elements
(Na, Mg, Ti,
Cu, Fe…)
Bond Type Triangle
Shows classification of bonding types based on
average electronegativity differences
http://chemed.
chem.purdue.
edu/genchem/
topicreview/b
p/materials/m
aterial1.html
Create your own CsCl
Model
• CsCl is an
ionic crystal
with a
coordination
number of
six. The red
and yellow
gummy bears
are the Cland the Blue
Gummy bear
is the Cs+
Questions
• What kinds of attractive forces exist
between particles in a) molecular
crystals; b) covalent network
crystals; c) ionic crystals; d) metallic
crystals
• A) hydrogen bonding, dipole dipole
forces, London dispersion forces
• B) covalent chemical bonds
• C) Ionic bonds
• D) Metallic Bonds
Questions
• Covalent bonding occurs in both molecular
and covalent network solids. Why do these
two kinds of solids differ so greatly in their
hardness and melting points?
• In molecular solids, relatively weak
intermolecular forces bind the molecules
in the lattice, so it requires little energy to
disrupt these forces.
• In covalent network solids, covalent bonds
join atoms into an extended network.
Melting or deforming a covalent network
solid requires breaking these bonds, which
requires a large amount of Energy
Questions
• A white substance melts with some
decomposition at 730 degrees
Celsius. As a solid, it is a
nonconductor of electricity, but it
dissolves into water to form a
conducting solution. Which type of
solid might this be?
• Must be ionic because of relatively
high melting point and properties as
a conducting solution
Questions
• Which will have a higher melting
point and why? A) B, BF3; B) Na,
NaCl; C) TiO2, Ti Cl4
• A) B, covalent network lattice like
C(s), versus weak dispersion forces
in BF3
• B) NaCl, ionic vs metallic bonding
• C) TiO2, higher charge on the O2