Transcript Atomic and Molecular Structure

Atomic and Molecular
Structure
By Bret Greenberg and Justin Larmore
Valence and Core Electrons
• Valence electrons – in the outermost shell of an
•
•
atom determine the chemical properties of the
element
Core electrons – in the inner shells and are not
involved in chemical behavior
Chemical reactions involve the loss, gain,
sharing or rearrangement of valence electrons
Periodic Group
Na
1A
Core
Valence
1s22s22p6
3s1
Total Configuration
[Ne]3s1
Lewis Dot Structure
 Octet Rule – the element is most stable with all
•
•
•
eight electrons
Molecules and ions with the same number of
valence electrons and same Lewis Structure can
be called isoelectronic
Bond order – the number of bonding pairs
shared by two atoms in a molecule
Bond order = # of shared pairs linking X and Y
# of X-Y links
Making Lewis Dot Structures
1. Take the lowest electronegative atom and put it in
the middle
2. Determine total number of valence electrons
3. Place single bonds between each pair of bonded
atoms
4. Place electrons in pairs around surrounding atoms
(if extra pairs of electrons, attach them to the
central atom)
5. If central atom does not have eight, make lone
pairs into double or triple bonds
Am I Polar?
CTn
C = central atom; T = terminal (outside atom)
• Not polar if all terminal atoms are identical and
all the terminal atoms are arranged
symmetrically around the central atom
• If one terminal atom is different, or if one of the
terminal positions is occupied by a lone pair, it
will be polar
Chemical Bonds
• Ionic = one or more valence electrons is
transferred from an atom to another
creating positive and negative ions
• Covalent = the sharing of valence
electrons between atoms
Electron Geometry
Linear
Trigonal Planar
Tetrahedral Trigonal Bipyramidal Octahedral
Molecular Geometry
Trigonal Planar
Tetrahedral
Bent
Trigonal Pyramidal
Trigonal Bipyramidal
Seesaw
T-Shaped
Bent
Octahedral
Linear
Square Pyramidal
Square Planar
Electromagnetic Spectrum
Longest to shortest wavelength: radio waves, microwaves, IR, UV, X rays, gamma rays
Highest to lowest frequency: gamma rays, X rays, UV, IF, microwaves, radio waves
Useful Equations
• Wavelength (m) * Frequency (s-1) = Velocity (m*s-1)
• E=h*v
•
E = Energy of Radiation (J/photon)
h = Planck’s constant = 6.6260755 x 10-34 J*s/photon
v = frequency of radiation (s-1)
Wavelength (m) = h/(mv)
m = mass (kg)
v = velocity (m/s)
h = Planck’s constant = 6.6260755 x 10-34 J*s/photon
Periodic Trends
• Atomic radii: the average distance to the
outside of the electron cloud (picometers).
Periodic Trends
• First Ionization Energy: the energy needed
to remove the outermost electron from a
neutral atom.
Periodic Trends Continued
• Ion Size: size of the ion compared to the
original atom
Size increases as you move down and
across the periodic table
• Electronegativity: ability to attract an
electron
Electronegativity increases as you go up
and across the periodic table
Quantum Numbers
N = principle quantum number ranges from 1
to infinity
l = the angular momentum quantum number
•
•
•
•
•
l characterizes the sub shell of the orbital
When l=0 sub shell label is s
When l=1, sub shell label is p
When l=2, sub shell label is d
When l=3, sub shell label is f
ml is the magnetic quantum number
• - l < ml < l
ms is the magnetic spin quantum number
• Equal to +1/2
Valence Bond Theory
• Valence bond theory: the idea that bonds
are formed by overlap of orbitals
• Sigma bond: covalent bond that arises
from the overlap of two s orbitals
• Bonding electrons lie along bond axis
• Pi bonds: a bond formed by sideways
overlap of py and pz atomic orbitals
Energy Level Diagram
Antibonding
• No counterpart in valence bond theory
• Higher energy level than regular bonds
• Cancels sigma bonds when filling out
molecular orbital energy level diagram
The End
Chemistry
is the
Shiznit!