Lesson 2 Crystalline Solids

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The SOLID
STATE:
Structures,
Properties; and
Bonding
Lesson 2
Learning Objectives
1. Compare the properties of crystalline and amorphous solids
2. Classify crystals according to the attractive forces between the component
atoms, molecules or ions (molecular crystals, covalent-network crystals, ionic
crystals and metallic crystals)
3. Relate the properties of different types of solids to the bonding or interaction
among particles in these solids; and
4. Predict the strongest force responsible for the formation of a given solid
How do atoms ARRANGE
themselves to form solids?
CRYSTALLINE
AMORPHOUS
Crystalline & Amorphous Solids
Terms
– Unit cell
– Lattice points
– Coordination number
– Packing efficiency
-
UNIT CELL
– the smallest group of atoms of a substance
that has the overall symmetry of a crystal of
that substance, and from which the entire
lattice can be built up by repetition in three
dimensions.
– The smallest subunit of a crystal lattice that
can be repeated over and over to make the
entire crystal.
Lattice
– is an array of points that defines the
positions of the particles in a crystal
structure.
Coordination Number
– In a crystal, the number of
nearest neighbors
surrounding a particle. In a
complex, the number of
ligand atoms bonded to the
central metal ion.
Packing Efficiency
– is defined as the percent of the total
volume of a solid occupied by
(spherical) atoms.
– It must always be less than 100% because
it is impossible to pack spheres (atoms are
usually spherical) without having some
empty space between them.
Types of Cubic Unit Cells
CRYSTALLINE
 Crystals have an orderly arrangement of their
constituent particles
 Crystals have a specific geometric shape with
definite edges
 Crystalline solids have a sharp melting point on
which they will definitely melt
 Crystals have a long order arrangement of their
particles
 Crystalline solids cleavage (break) along
particular points and directions.
 also known as True Solids
AMORPHOUS
 particles are randomly organized
 have no geometry in their shapes
 amorphous solid will have a range of
temperature over which it will melt
 have a short order arrangement. Their particles
show a lot of variety in their arrangement.
 cleavage into uneven parts with ragged edges.
 Super-Cooled Liquids.
Examples of Non-crystalline Solids
CHARCOAL
RUBBER
PAPER WEIGHT
PLASTIC CONTAINER
Examples of Crystalline Solids
Salt crystals
Brown Sugar crystals
Snow flakes
Amythest cluster
 What are the four types of crystals? What form of
unit particles makes up each type of crystal?
What forces bind the unit particles of each type of
crystal?
What are the properties of each type of crystal?
Metallic Crystals
– Metallic crystals are made of atoms that readily lose electrons to form positive
ions (cations), but no atoms in the crystal would readily gain electrons.
– The metal atoms give up their electrons to the whole crystal, creating a structure made
up of an orderly arrangement of cations surrounded by delocalized electrons that move
around the crystal. The crystal is held together by electrostatic interactions between the
cations and delocalized electron. These interactions are called metallic bonds. This
model of metallic bonding is called the “sea of electrons” model
METALLIC CRYSTALS
Observed property
Dense
High melting point
Good electrical
conductor
Good heat conductor
Malleable and ductile
Lustrous
Inference about the structure
Atoms are packed close together.
Strong attractive forces hold the
atoms in the crystal.
Charged particles move through the
crystal.
Particles can move through the
crystal.
When the crystal is deformed or
stress is applied, the attractive forces
are not broken.
Light is easily absorbed and emitted
back.
IONIC CRYSTALS
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