Lewis Structures Flashcards
Octet rule
Most atoms form bonds in order to obtain 8 valence electrons
Exceptions- Hydrogen 2, boron 6
How to find valence electrons
Down columns
Lewis dot structure
A molecular model that uses symbols and bonds to show relative positions of atoms
Steps to determine Lewis structure (1)
1-predict draw location
H always end
First element listed is normally central atom
Steps to determine Lewis structure (2)
Find number of valence electrons needed and then number they have, subtract the two to find the difference
Steps to determine Lewis structure (3)
Use the difference to divide it by two which gives number of bonds
Steps to determine Lewis structure (4)
Draw in bonds and then unpaired electrons to central atom
Steps to determine Lewis structure (5)
Count number of electrons to check work, should equal number have
True or false, most bonds are a blend of ionic and covalent characteristics
True
How to find bond type
Difference in electronegativity (subtract)
Electronegativity difference number for polar covalent
1.7-.3
Electronegativity difference number for no polar covalent
0-.3
How to find more polar using periodic table
Bigger difference between the atoms means more polar
Non polar covalent bond
Electrons Shared equally Symmetrical electron density Usually identical atoms ( • •) Ex CH
Polar covalent
Electronegativity are shared unequally
Asymmetrical electron density
Results in partial charges dipoles
( • Bigger •) neg
What is the molecular geometry of covalent molecules is based on
Valence shell electron pair repulsion theory
VSEPR
What results in the specific molecular shape and bond angles
Electron pairs arrange themselves to be as far as possible
Difference between unshared electrons and shared pairs space
Lone pairs take up more space then shared pairs
2 atoms to central, no lone pairs
Shape?
Bond angle?
Example?
Linear
180
Straight line
3 atoms to central, 0 lone pairs
Shape?
Bond angle?
Example?
Triangular planar
120
O
O -S-O
4 atoms to central, no lone pairs
Shape?
Bond angle?
Example?
Tetrahedral
109.5
H
H-C-H
H3 atoms to central, 1 lone pairs
Shape?
Bond angle?
Example?
Trigonometry pyramidal
107
H
H-N-H
:2 atoms to central, 2 lone pairs
Shape?
Bond angle?
Example?
Bent
104.5
Cl-S::
Cl
When is it polar
When no symmetrical (lone pairs or different atoms)
Or uneven sharing of electron pairs due to large difference in electronegativity between two atoms in the bond
IMF stands for
Intermolecular forces
Attractive forces between two molecules of the same compound
What does polarity depend on
Attraction
Which is stronger, polarity or chemical bonds
Chemical bonds
What IMF force do all molecules have
London dispersion
List weakest to strongest of imf forces
Weakest-London dispersion Dipole dipole Hydrogen bonding (Fstrongest)
London dispersion force
Attraction between two instantaneous dipoles
Asymmetrical electron distribution
All atoms
London dispersion diagram
Two separate oval molecules
For London dispersion how to tell a tie
Higher molar mass is a stronger IMF
Dipole dipole definition
Attraction between two permanent dipoles
Polar
Diagram for dipole dipole
Hydrogen bonded to carbon
How to tell a tie from dipole dipole
Greater difference in electronegativity means stronger IMF
Hydrogen bonding definition
Attraction between H-FON
Polar very strong
Not Chem bond
How to break a tie for Hydrogen bond
Increase in lone pairs in crease in IMF
FON order, F strongest IMF
IMF with phase change
Weaker when
Boiling point is lower
Melting point lower
Evaporation faster
IMF with phase change is stronger when
Boiling point higher
Melting point high
Evaporation slower
