4: Atomic and Molecular Structure
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coulombic potential does what
coulombic potential around the positive nucleus defines the energy and possible position of the electrons, which in turn define all possible properties of atoms and molecules.
second law of thermo determines
what happens or doesnt happen
overview of Bohr atomic model
• nucleus has Z = #protons, N = # neutrons mass: A = Z+N proton and neutron mass»_space; electron mass standard probability distribution for the place of electrons (distance from nucleus vs probability )
what are the quantum numbers
n, l, ml, ms n = principal # l = angular momentum qn, l= 0, 1, 2… (n-1) - l is limited by n ex: n= 2: l = 0, 1 m = magnetic quantum # - component of orbital angular momentum along a specific direction m = -l,- (l-1), -(l-2)….0,…. (l-2), (l-1), 1 m has 2l+1 possibilities ms: spin #, +/- 1/2
Schrödinger eqn
wave function = Y prob density function = Y^2 Schrödinger eqn (total energy = kinetic + potential energy) EY = HY
hydrogen atom soln of schrodinger
slide 11-13
orbital fillin principles - aufbau - hund’s rule - pauli exclusion principle
aufbau: electrons occupy orbitals of increasing energy Hund’s rule: electrons occupy all degenerate orbitals (same n and l quantum numbers) before putting two electrons in the same orbital pauli exclusion principle: no two electrons have the same set of 4 quantum numbers
do elements have a stable electron configuration ?
most dont, bc valence shell is usually not filled completely, so there will be net attractive forces to a similar neighbour noble gases have full valence shells, so theyre stable
what can we say abt elements of similar valence structure ?
similar properties
review orbital filling, and filling my periodic table
def electronegativity
tendency of a nucleus to pull an electron cloud towards it. depends on how shielded the nucleus is by the core electrons. it has important effects on chemical bonds
what side of periodic table has lower electronegativity ?
left
explain metallic bonding
atomic orbitals combine to form a delocalized electron cloud shared by a large number of electrons
def ionic, covalent bonds
Ionic: elements w greatly varying electronegativity bond, one takes neg charge, one takes pos covalent: similar electronegativity, the electron pair becomes shared in molecular orbital
van der Waals bonding hydrogen bonding
van der walls: weak bonding induced by fluctuating or permanent molecular dipoles hydrogen bonding: bonding between hydrogen protons and an available electron pair
study all curves in notes
on a force vs interatomic seperation curve, where is the ro, what does the well represent ?
ro = the bond length at the point where the sum of forces = 0 (r at x intercept) well = work done
what relationship do the force vs r and potential vs r curve share?
potential curve is the integral of the force vs r curve
what is the main type of bonding in ceramics
ionic
what material has covalent bonding
• polymers have it within each chain (but van der walls between each molecule) • diamonds
covalent bond hybridization
combining of s and p orbitals to form set of equivalent orbitals for bonding
metallic bonding (longer explanation) what does this bonding structure impact?
sea of delocalized valence electrons which move relatively freely around the ion cores constituted of the protons and core electrons. the bonds are non-directional. this bonding structure has an impact on electrical thermal, mechanical properties
which bonds are directional? non-directional?
directional: covalent, secondary non-directional: ionic, metallic
the force and potential created by chemical bonds influence what properties
• melting temp • Elastic modulus • thermal expansion coefficient • hardness • etc