Bonding
Bond order
(# bonding electrons - # antibonding electrons)/2 OR # electron pairs shared btwn two atoms
Bond breakage is exothermic or endothermic?
ENDOTHERMIC
Heat is a reactant for an _________ reaction
ENDOthermic
Formation of bonds is EXO or ENDO?
EXOTHERMIC
Heat is a product for an __________ reaction
EXOthermic
Formal charges are used to decide which Lewis structure is most probable when more than one can be drawn.
To calculate the formal charge count up all the electrons that belong to the atom itself, then subtract this value from the valence electrons for that atom. If you are short of the valence # then you get a + charge If there is an overage in the valence # you get a - charge
Calculate the heat of reaction for the complete combustion of one mole of methane. Use the bond energy data from the book.
Work this one out on paper and turn in to me.
What is the bond order for carbon-oxygen bond in CO?
bond order is 3 b/c it is a triple bond
Enthalpy of a reaction
ΔH (rxn) = Energy input - Energy output ΔH (rxn) = ∑(bond energy reactants) - ∑(bond energy products) OR ΔH (rxn) = sum of BE broken - sum of BE formed
Heat of reaction may be calculated using enthalpies of formations from tables of values
ΔH = ∑( ΔH f )products - ∑(ΔH f ) reactants
What is the bond order of the hydrogen oxygen bonds in water?
1
What is the bond order in oxygen?
2
What is the bond order in N₂?
3
What is the first period of the elements that would allow for an expanded octet?
3rd period b/c it is the first shell that allows 'd' orbitals
What is a coordinate covalent bond? Check out NH₃ + H⁺
A covalent bond in which one atom donates both electrons used in the chemical bond. N and P are good examples of atoms that have a lone pair which can be used to coordinate covalently bond.
Valence bond theory
Bonds are formed by overlapping atomic orbitals on adjacent atoms. Hybridization is part of this theory. Hybridization rationalizes the predicted structure of the molecule. It is NOT predictive. You must use VSEPR to get the structure first, then use hybridization to rationalize the bonding.
What is the bond order of the carbon hydrogen bond in methane, CH₄?
C-H is a single bond ∴ bond order is 1
Write the C-O , C=O , C≡O bonds in order of increasing length.
C≡O < C=O < C-O Single bonds are longest; Triple bonds are the shortest
ΔH = +
Endothermic
ΔH = -
Exothermic
T or F: The bond order of a double bond is 4
FALSE: bond order is 2 for a double bond
T or F: Lewis structures of ions are enclosed in parenthesis with the charge placed in upper right corner.
FALSE: use BRACKETS ex. [ ]⁻ ... NOT ( )⁻
Enthalpy of a reaction is also called ...
Heat of a reaction
T or F: Energy is released when bonds are formed.
TRUE
T or F: Formal charges must combine to give the charge on an ion or be zero for a compound
TRUE
T or F: Resonance structures use a double headed arrow between the different structures.
TRUE
T or F: Single bonds are the easiest to break
TRUE
T or F: Triple bonds are the shortest bonds
TRUE
T or F: hybridization helps explain the different bonding in carbon compounds
TRUE
T or F: the bond order can be a fraction
TRUE; the bond order in ozone is 3/2 b/c of resonance; the bond order in carbonate ion is 4/3 b/c of resonance
Bond length decreases with increasing bond order. Explain.
The added electron density between the nuclei reduces the distance btwn nuclei, hence shortens the bond
Draw the Lewis structure for NO a stable compound. What is odd about it? (pardon the pun)
Work this one out on paper and turn in to me.
Draw the Lewis structure for the nitrite ion.
Work this one out on paper and turn in to me.
Draw the Lewis structures for XeO₃ an explosive compound of xenon. Decide which structure(s) is best.
Work this one out on paper and turn in to me.
Repeat the combustion of methane, but this time calculate the heat of rxn using enthalpy of formation data found in your book.
Work this one out on paper and turn in to me.
(ΔH f) of an element in its standard state is ...
ZERO
What is the bond order for carbon-oxygen in CO₂
bond order is 2 b/c it is a double bond
The BEST Lewis structure is the one that has the smallest number of non-zero formal charges AND
has the smallest magnitude of charges AND will not have a positive charge on an electronegative atom or vice versa.
I found this site on bonding: check it out:)
http://cosm.georgiasouthern.edu/chemistry/general/molecule/resonan.htm
Hybridization
mixing of atomic orbitals to make new 'hybrid' orbitals of the same # with equal energy. ex. mix an 's' and a 'p' and you get two hybrid orbitals of equal energy that have s and p character and are called 'sp' orbitals
Resonance
occurs when there is more than one terminal atom that can form multiple bonds. The actual molecular structure is a "hybrid" of the Lewis structures drawn on paper.
bond dissociation energy
the energy required to break a chemical bond btwn gaseous atoms. Always Endothermic
Heat absorbed by a reaction tells you that ...
the rxn is ENDO and the vessel will feel cooler than before.
Heat released by a reaction tells you that...
the rxn is EXO and the vessel will feel warm (hot) when touched.
Which bonds require more energy to break? single, double, or triple bonds
triple require the most energy since the atoms are held together more tightly with added electron density btwn nuclei.
