Ranking bond types from strongest to weakest Note: I've already handed this in for homework and got the question wrong but don't understand why. Not looking for someone to do my homework for me, just trying to flesh out an area where I'm not yet proficient.
This is problem 4.10 from the book "Nanotechnology: Understanding Small Systems" 2nd ed. by Rogers, Pennarthur, and Adams. 
The exact wording of the problem states: 
"Rank the following bonds from strongest to weakest and provide the bond energy: the bond between hydrogen an oxygen in a water molecule; the bond between sodium and chloride in the NaCl molecule; the bond between atoms in a metal; the van der Waals bond between adjacent hydrogen atoms." 
I've found the exact bond strength of 3 of 4 of these. 
Na+ - Cl- bond = 830 zJ or 8.3E-19 J 
H-O bond = 760 zJ or 7.6E-19 J 
H-H bond = 0.14 zJ or 1.4E-22 J 
What I cannot find is the bond strength for metal-to-metal atoms. I tried specifically looking for copper, silver, and iron and couldn't find the bond strength between atoms. 
To complicate things further, this question has been asked numerous times in various iterations and other answers have stated that covalent bonds are stronger than ionic bonds, which are in turn stronger than metallic bonds. Everyone agrees H-H bonding is weakest. 
So is it just the case that Na-Cl is a particularly strong ionic bond and H-O is a particularly weak covalent bond such that this particular ionic bond is stronger than this particular covalent bond? Or are the other answers incorrect?
I should probably also note that based off of copper's heat of vaporization of 3630 J/g and its molar mass of 63.546 g/mol I calculated a bond strength of 383 zJ and WRONGLY concluded: 
ionic > covalent > metallic > H-H (van der Waals) 
So I got the question marked incorrect which probably means I didn't do the calculation for copper's bond strength correctly.
 A: The lattice
energies of ionic
compounds are
relatively large.
The lattice energy
of NaCl, for
example, is 787.3
kJ/mol , which is only slightly less
than the energy given off when
natural gas burns. The bond
between ions of opposite charge is
strongest when the ions are small.
For example, an HO–H bond of a
water molecule (H–O–H) has 493.4
kJ/mol of bond-dissociation
energy, and 424.4 kJ/mol is needed
to cleave the remaining O–H bond.
The bond energy of the covalent
O–H bonds in water is 458.9 kJ/
mol , which is the average of the
values.
Total for water 493+424 = 917.8
Clearly for 
H2O>Nacl 
For metals 
you need to plus BE along with E for vaporisation.
A: So I found some information in the Chemistry stackexchange that suggests that the correct order is:
covalent > ionic > metallic > VDW
The answer is provided here. However, it still doesn't make sense to me because I've looked up the values for these bond types and clearly the ionic bond in NaCl is strong than the covalent bond in water between hydrogen and oxygen.
I kind of give up on sorting this out because it seems like anywhere I check, there are people giving BOTH answers. Makes no sense!
