Chemistry Exam 3 Flashcards
what is electronegativity?
the ability of atoms in a molecule to attract electrons to itself
What is the electronegativity trend?
Up and to the right on the periodic table
What is the most electronegative element?
Fluorine
What group of elements are not assigned electronegativity?
noble gases
When talking about the electronegativity trend what happens when the elements are right next to each other? and what is the exception?
If the elements are right next to each other they are non-polar. And the exception is when the atoms are in row 2
Non-polar Covalent Bond
electrons are shared EQUALLY (example: Cl2)
Polar Covalent Bond
electrons are shared UNEQUALLY (example: HCl)
Ionic Bond
electrons are NO LONGER SHARED
In lewis structures what atom goes in the middle?
The LEAST electronegative element that isn’t hydrogen
What is formal charge?
the charge that an atom (in a molecule) would have if all of the atoms had the same electronegativity
What is the formal charge formula?
FC= valence electrons - lines - dots
What is the best lewis structure?
The one with the most charges closet to oxygen & puts a negative charge on the most electronegative atom
What are resonance structures?
When there is more than one lewis structure for a molecule that differs only in the position of the electrons
Rules of Resonance Structures
- Resonance Structures must have the same conductivity.
- They must have the same number of electrons
- Formal charges must total the same
- Hydrogen can never be a central atom (usually carbon is)
What are some things that make a better resonance structure?
Better structures have:
1. fewer formal charges
2. smaller formal charges
3. negative formal charge on the more electronegative atom
What are some exceptions to the octet rule?
- ions or molecules with an odd number of electrons (Examples: ClO2, NO, and NO2)
- ions or molecules with less than an octet (hypovalence) (Examples: BF3)
- ions or molecules with more than eight valence electrons (hypervalent) (Examples: PCl5)
What is hypovalance?
less than an octet
What is hypervalance?
more than an octet (extra valance)
Where are hypovalance atoms usually found?
groups 2 & 3
Where are hypervalance atoms found?
third row or below
What is the VSEPR Model?
it stands for valance shell electron pair repulsion, and it dictates molecular shapes based on electrons
Practice: How many electron domains does each compound have?:
1. CO2
2. O3
3. PCl3
- 2 electron domains
- 3 electron domains
- 4 electron domains
What is the predicted bond angle for Linear electron domain geometry?
180 degrees
What is the predicted bond angle for Trigonal Planar electron domain geometry?
120 degrees
What is the predicted bond angle for Tetrahedral electron domain geometry?
109.5 degress
What is the predicted bond angle for Trigonal bipyramidal electron domain geometry?
120 & 90 degrees
What is the predicted bond angle for Octahedral electron domain geometry?
90 degrees
What does 3e- domains equal? (molecular geometries)
Trigonal Planar e- geometry
What does 2e- domains +1 lone pair equal?
Bent molecular geometry
What does 2e- domains equal?
Linear e- geometry
What does 4e- domains equal?
Tetrahedral e- geometry
What does 3e- domains +1 lone pair equal?
Trigonal planar molecular geometry
What does Molecular Polarity depend on?
Both the polarities of the individual bonds and the geometry of the molecule
Are carbon-hydrogen bonds polar or non-polar?
They are non-polar
What is the hybrid orbital for 3 electron domains (trigonal planar geometry)?
sp^2
What does blending an s and two p orbitals produce?
three sp^2 hybrid orbitals
What is the hybrid orbital for 4 electron domains (tetrahedral geometry)?
sp^3
What does blending an s and all 3 p orbitals produce?
four sp^3 hybrid orbitals
What is the hybrid orbital for 5 electron domains (trigonal bipyramidal geometry)?
sp^3d
What is the hybrid orbital for 6 electron domains (octahedral geometry)
sp^3d^2
What is hybridization only related to?
electron geometry
Is a single pond a pi or sigma bond?
sigma bond
Are double bonds a pi or sigma bond?
double bond are 1 sigma + 1 pi bond= pi bond
Are triple bonds a pi or sigma bond?
Triple bonds are 1 sigma + 2 pi bonds= pi bond
What is a physical change?
changes that alter only the state or appearance, but not the composition (no bonds are broken or reformed)
What is a chemical change?
changes that alter the composition of matter (bonds are broken or reformed)
What side of a chemical equation are reactants on?
the left side
What side of a chemical equation are products on?
the right side
What has to happen in a chemical reaction?
conservation of matter and equal number of atoms on both sides
Practice balancing equations
reference notes for practice problems
what does (s) stand for? (states of matter)
solid
what does (l) stand for? (states of matter)
liquid
what does (g) stand for? (states of matter)
gas
what does (aq) stand for? (states of matter)
dissolves in an aqueous solution
Practice stoichiometry
reference notes for practice problems
How do you find out what is the limiting reactant in a chemical reaction?
- Do two (or more based on given # of reactants) stoichiometry problems
- The one that makes the least product is the limiting reagent
Practice limiting reactant problems
Reference notes for example
What are the reactants in a combustion reaction?
they are usually carbon and always oxygen
What are the products in a combustion reaction?
always H2O and mostly CO2
What is the reactant in alkali metal reactions?
an alkali metal
