Lesson 7 Flashcards
Categories of Solids
Crystalline Solid
Amorphous Solid
a solid that Has rigid and long-range order and its atoms, molecules, or ions occupy specific
positions.
crystalline solid
In crystalline solid, The arrangement of particles is such that the net attractive intermolecular forces
are at their ___________.
The molecular forces responsible for the stability of a crystal can be ionic forces,
covalent bonds, van der Waals forces, hydrogen bonds, or a combination of these
forces.
maximum
A solid where there is an absence of a well-defined arrangement and long-range
molecular order
amorphous solid
Atoms or ions (described as crystalline structures) are thought of as being solid
spheres having well-defined diameters. This is known as the ____________ in which spheres representing
nearest-neighbor atoms touch one another.
atomic hard-sphere model
means a three- dimensional array of points coinciding with atom positions or
sphere centers.
lattice
A __________ is the basic structural (repeating) unit of a crystalline solid.
unit cell
Angle α is defined by edges ________
Angle β by edges _______
Angle γ by edges__________
-b and c
-a and c
-a and b
The Seven Types of Unit Cells
simple cubic
tetragonal
orthorhombic
rhombohedral
monoclinic
triclinic
hexagonal
____________ is a crystal structure with atoms located at each of
the corners and the center of all the cube faces.
face-centered cubic (FCC)
Some familiar metals having this crystal structure are ___________________
copper, aluminum, silver, and
gold.
The is a crystal structure with atoms located at each of
the corners and the center of all the cube faces.
face-centered cubic (FCC)
FCC area formula
a=2Rsqrt2
number of atoms per unit cell formula
Ni + (Nf/2)+(Nc/8)
Number of atoms in FCC
4
Two Important Characteristics of Crystal Structure
-coordination number
-atomic packing factor
______________ (for metals) wherein each atom has the same
number of nearest-neighbor or touching atoms;
coordination number
is the sum of the sphere volumes of
all atoms within a unit cell (assuming the atomic hard-sphere model) divided
by the unit cell volume.
atomic packing factor
apf formula
volume of the atoms in a unit cell/ total unit of cell volume
apf of fcc
0.74
_____________ is a crystal structure that has a cubic unit cell with atoms located at all eight corners and a single atom
at the center of the cube.
body-centered cubic (BCC)
bcc area
4R/sqrt3
number of atoms of bcc
2
atomic packing factor of bccsimple cubic (SC) crystal structure.
0.68
The possibility of a unit cell that consists of atoms placed only at the corners of a cube
do exist and it is called the ___________
simple cubic (SC) crystal structure.
the only simple-cubic element that has a
relatively low atomic packing factor.
polonium
In the _____________________, the top and bottom faces of
the unit cell is consist of six atoms that form regular hexagons and surround a single
atom in the center.
hexagonal close-pack crystal structure (HCP)
number of atoms in hexagonal close-pack crystal structure (HCP)
6
refers to the scattering of X-rays by the units of a crystalline solid.
x-ray diffraction
In 1912, _______, a German physicist recommended that
since the wavelength of X-rays is comparable in magnitude to the
distances between lattice points in a crystal, then the lattice
should be able to diffract X-rays.
Max von Laue
Constructive interference (a) and destructive interference (b)
constructive: same direction kaya may sum
destructive: iba direction kayawalang sum
Atoms in the
crystal absorb some of the
incoming radiation and then
reemit it; the process is called
the ______________
scattering of X rays.
An ____________ basically tells us the relative electron densities at
various locations in a molecule.
electron-density contour map
