Molecules/Energy/Polarity
In bonded atoms, are electrons usually shared equally
Unless the two atoms are identical, one atom typically has more electron-attracting power (or electronegativity) then the other
What happens to an atom with a higher electronegativity in a molecule
it has a negative partial charge because it is "holding on to" more than half of the electrons being shared in the molecule
What happens to an atom with a lower electronegativity in a molecule
it has a positive partial charge because it is "holding on to" less than half of the electrons being shared in the molecule
Name and bond angle of molecule with a steric number of 2
linear; 180; non-polar
What is the relationship between electron density and bond order
more electrons= higher bond order
Partial Charge equation
partial charge= Va-Na-paBa Va= number of valence electrons Na= number of unbonded electrons (loan pairs) pa= (ENa/ENa+ENb) Ba= number of bonding electrons (number of bonds)
What phase of matter has the strongest intermolecular forces
solid
Name and bond angle of molecule with a steric number of 4
tetrahedral; 109.5; non-polar
Enthalpy
the amount of energy released or absorbed in a chemical process; represented by ΔH
Bond energy
the energy required to break 1 mol of a specific chemical bond
If two covalent bonds are compared, how is it determined which is more polar
the one that results in partial charges with larger magnitude is considered more polar
What must the magnitudes of the different atoms' partial charges in a molecule equate to
the overall net charge of the molecule; thus if the net charge is zero the magnitude of both atom's partial charges must be equal
What is the relationship between bond order and bond length
the smaller the BO the longer the bond length
What does it mean when ΔH is negative
there is a release of energy during a chemical process and the reaction is exothermic
What is the relationship between AVEE and EN
they are proportional with one another with some slight deviation. On avg. the difference between EN and AVEE is a factor of 1.8
Name and bond angle of molecule with a steric number of 3
trigonal planar; 120; non-polar
Name and bond angle of molecule with a steric number of 4 loan pair 1
trigonal pyramidal; 109; polar
Endothermic reaction
when energy (heat/light) is absorbed
exothermic reaction
when energy is released (usually in the form of heat or light)
dipole moment equation and explanation of variables
μ= q * d μ= dipole moment q=magnitude of the two charges d= the distance (vector) between two charges
Bonds that have a higher bond energy...
Are stronger bonds
What is the "best" lewis structure
-the one with the fewest charges
7-Step method
1) Electrons needed for Octet/Duet rule2) Valence electrons3) Electrons shared= #1-#24) Bonds= #3/25) Add loan pairs6) Partial charge (higher X = partial charge negative; lower x = partial charge positive)7) Formal charges= valence electron- electrons assigned (box)
How do you draw a reaction energy diagram
1) consider the reaction taking place 2) break apart all of the reactant molecules and calculate their ΔH. Pay attention to coefficients 3) represent the atoms in terms of their moles 4) resemble those atoms into the product molecules and calculate their ΔH. Pay attention to coefficients 5) Calculate difference between the ΔH values
covalent bond
A chemical bond that involves sharing a pair of electrons between atoms in a molecule
polar covalent bond
A covalent bond in which electrons are not shared equally; there is a difference in electronegativity between the atoms
Electronegativity
A measure of the ability of an atom to attract electrons
Equation for AVEE and description of its components
AVEE= (aIs+bIp) /(a+b) a and b are the numbers of electrons in the s and p subshells of the valence see, Is and Ip are the ionization energies of those subshells
What is the periodic trend of AVEE and why
Across period: increases as you move right to left b/c core charge/nuclear charge increases Down a row: decreases because distance from nucleus increases
Why do homonuclear molecules have non polar bonds
Because there is no difference in electronegativity
How do you calculate bond order for regular lewis structures and resonance structures
Both: count the number of bonds and divide that number by the number of regions they are in
How to determine if you can expand an octet
Check to see if valence electron capacity for central atom has been reached. If not, you can rearrange the number of bonds used
How can a lewis structure demonstrate covalent and ionic bonds
Covalent: Based on the electron density-if the different atoms are all connected within the "cloud" of electron density Ionic: Based on the electron density- when the atoms of the lewis structure are detached and in separate "clouds" of electron density Ionic also based on charges : + and - charge indicate ionic
Is breaking bond endo or exothermic? Why?
Endothermic because energy is needed (or absorbed) too break atoms, being held together by bonds, apart
Is bond forming endo or exothermic? Why?
Exothermic because when bonds are formed they release energy (the same amount of energy required to break them)
exceptions to the octet rule
H= 2 electronsBe= 4 electronsB= 6 electrons
What does the average ionization energy of the valence electrons tell you/give insight to?
How tightly an atom holds its valence electrons Higher a valence electron's ionization energy, harder to remove it/tighter it is held
In terms of AVEE why is Na more likely to become NA+ than O is to form O+
O AVEE is greater than Na AVEE. More energy is required to remove an e from O than Na
What is the periodic trend of electronegativity
Same as AVEE
Why does H(g) has a ΔH=0 and H2(g) has a ΔH=-435.30?
There is no change in enthalpy b/c there is no chemical change in the production of H(g)
non polar covalent bond
a bond between identical atoms
dipole moment
a measure of the separation and magnitude of the positive and negative charges in polar molecules
Name and bond angle of molecule with a steric number of 3 loan pair 2
bent; 109; polar
Name and bond angle of molecule with a steric number of 3 loan pair 1
bent; 120; polar
What does it mean when ΔH is positive
energy is being absorbed during a chemical process and the reaction is endothermic
How do you calculate bond length for resonance structures
find the average of the lengths of different bonds associated with the structure
Intermolecular forces
forces of attraction between molecules
What phase of matter has the weakest intermolecular forces
gas
Atoms with a smaller atomic radius...
have shorter bonds and are therefore stronger