module 4 Flashcards
are composed of electrons, protons, and neutrons.
Atoms
The magnitude of each charged
particle in an atom is
1.6 × 10-19 Coulombs.
is the amount of matter that has a mass in grams equal to the atomic mass
in amu of the atoms.
mol
The number of atoms in a mole is called
Avogadro number, Nav = 6.023 × 1023.
Most solids have atomic densities around
6 × 1022 atoms/cm3
The mean
distance between atoms is the_____ This is an important number
that gives the scale of atomic structures in solids.
inverse of that, or 0.25 nm.
The inter-atomic bonds are primarily of two kinds what are they?
Primary bonds and Secondary
bonds.
Covalent and Metallic bonds are relatively very strong, and grouped as
primary bonds,
van der Waals and hydrogen bonds are relatively weak, and
termed as
secondary bonds.
Metals and Ceramics are entirely held together by
primary bonds
They provide
the links between polymer molecules in polyethylene (and other polymers) which make
them solids.
secondary bonds
This bond exists between two atoms when one of the atoms is negative
(has an extra electron) and another is positive (has lost an electron). Then there is a
strong, direct Coulomb attraction.
Ionic Bonding:
electrons are shared between the atoms, to
saturate the valency. The simplest example is the H2 molecule, where the electrons spend
more time in between the nuclei of two atoms than outside, thus producing bonding.
Covalent Bonding:
are characterized by high thermal and electrical conductivities.
Thus, neither covalent nor ionic bondings are realized because both types of bonding
localize the valence electrons and preclude conduction. However, strong bonding does
occur in metals.
Metallic Bonding:
Since the electrons may be on one side of the atom
or the other, a dipole is formed: the + nucleus at the center, and the electron outside.
Since the electron moves,
the dipole fluctuates.
