Electro- negativity
What is the definition of electronegativity?
Relative ability of a bonded atom to attract shared electrons
What is a polar covalent bond?
A covalent bond in which the shared electron pair is not shared equally, but remains closed to one atom than the other.
Bond-breaking is an ____-thermic process and bond-forming is an ____-thermic process.
Endo, Exo
True or False: Metals are good conductors of electricity in the solid state, but not the liquid state. Why?
False. Metals are good conductors of electricity in both the solid and liquid states because the electron sea is mobile in both phases.
Depict HCl as a polar bond.
Arrow pointing from H to F, or using positive delta on the H and negative delta on the F.
What element has the highest electronegativity in the periodic table and with what value?
F, 4.0
Unequal sharing of electrons causes the more electronegative atom of the bond to be partially _______ and the less electronegative atom to be partially ______.
Negative, Positive
What is the formula to calculate enthalpy change using bond energies?
Delta H= Sum(Bonds breaking/Reactants) - Sum(Bond forming/Products)
Why can metals be shaped without breaking?
The electron sea allows the metal ions to slide past each other.
What is the formula to calculate oxidation number?
ON = # of valence electrons - (# of shared electrons + # of unshared electrons)
Electronegativity _______ down a group and _______ across a period. Why?
Decreases, Increases, Follows opposite trend as atomic size.
A bond with a difference in electronegativity of 0.1 is most likely which type of bond?
Non-polar covalent
True or False: In an endothermic reaction, the total bond energy in the products is less that in the reactants. Why?
True. Delta H results negative. Energy input to break the bonds is higher than energy output when forming the bonds.
Why are the melting points of metals only moderately high?
The melting process does not break the metallic bonds.
True or False: When calculating oxidation number, the more electronegative atom is assigned none of the shared electrons, while the less electronegative atom is assigned all of the shared electrons.
False, the MORE electronegative atom is assigned ALL the shared electrons.
Cl
Which of the following covalent bonds is the most polar: B-H, N-H, P-H, Al-H?Electronegativity Values: H=2.2, B=1.57, N=3.04, P=2.19, Al=1.61
N-H (0.84)
Estimate the enthalpy change in the following reaction:
H-H + F-F -> H-F + H-F
Bond energies (kJ/mold): H-H=436, F-F=155, H-F=567
-543 kJ/mol
Melting points ______ down a group and ______ increase across a period.
Decrease, Increase
Calculate the oxidation number of H in HCl.
ON = 1 - (0 + 0) = +1
Rank the following elements in order of increasing electronegativity: O, Cs, C, Sr, N
Cs Sr C N O
Which of the following has covalent bonding exhibiting the greatest polarity: S8, LiF, NF3, PF3, H2?
Estimate the enthalpy change in the following reaction:
H2 + Cl2 -> 2HCl
Bond energies (kJ/mol): H-H=436, Cl-Cl=242, H-Cl=431
-184 kJ/mol
Describe metallic bonding
Calculate the oxidation number of Cl in HCl.
ON=7 - (2 + 6) = -1