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The Relative Strength of Chemical Bonds
Name _______________________________________ Coursework Stamp #
Can we use macroscopic properties like boiling points and
melting points to infer the strength of chemical bonds?
Why? Chemical bonds can be categorized into four main groups: covalent, ionic,intermolecular, and metallic. Understanding these four categories of bondsallows chemist to explain and more importantly predict the properties ofsubstances and possible chemical reactions. In addition, chemistry dealspredominantly with things that we cannot see directly. We have to infer theproperties from evidence that we can see and measure.
Today you will be
practicing that skill.Complete these summaries AFTER you have finished this POGILSummarize what you learned from
Model 1
Summarize what you learned from
Models 2‐
Summarize what you learned from
Model 6
Use the scale below to rank the relative strength of the bonds.
Strongest
Weakest
2
Model 1: Review of Bond Types So far you have learned that differences in electronegativity are used todetermine some of the types of bonds that forms between two atoms. Beloware diagrams of ionic and covalent compounds.
Sodium Chloride
Water
Type of Bond
Difference in
electronegativityis large, medium,
or small
Electrons are shared evenly, shared unevenly,
or transferred
Types of Atoms
that typically
form this kind of
bond
Ionic
LARGE
TRANSFERRED
METALS &
NONMETALS
Polar Covalent
MEDIUM
SHARED
UNEVENLY
NONMETALS &
NONMETALS
Non‐polarCovalent
SMALL
SHARED EVENLY
NONMETALS &
NONMETALS
Using as much detail as you can, describe what holds atoms together in anionic bond like NaCl. Use the diagram above to help.
Answers will vary, but should include discussion about how the largeelectronegativity differences between anions & cations cause electrons to betransferred. 2.
Using as much detail as you can, describe what holds atoms together in acovalent bond like H
2
O.
Answer will vary, but should include discussion about how a relatively largeelectronegativity difference between nonmetals creates an uneven sharing ofelectrons.
Na
+
Cl
‐^
Na
+
Cl
‐
Na
+
Cl
‐
Na
+
Cl
‐^
Na
+
Cl
‐^
Na
+
Cl
‐ Na
+
Cl
‐^
Na
+
Cl
‐
Na
+
Cl
‐
Na
+
Cl
‐^
Na
+
Cl
‐^
Na
+
Cl
‐
Ionic Bonds
Covalent
Bonds
Intermolecular Forces
(hydrogen bond)
Explain what holds the atoms together in a metallic bond.
Metallic bonds are created between the positive protons in the nucleus to the “sea ofelectrons” moving around the positively charged nuclei.
How would you expect the strength of metallic bonds to compare with
the strength of covalent bonds? Explain your reasoning.
I would expect metallic bonds to be weaker than covalent bonds, because of their lowelectronegativities don’t pull the atoms closer together.
4
Model 2: Melting and Boiling Points
Nameformula
Types ofBonds
MeltingPoint (˚C)
BoilingPoint (˚C)
Sodium chlorideNaCl
Ionic
Copper(II) sulfideCuS
Ionic
Magnesium oxideMgO
Ionic
Calcium bromideCaBr
2
Ionic
Iron(III) sulfateFe
2
(SO
4
3
Ionic & Covalent
Sodium phosphateNa
3
PO
4
Ionic & Covalent
WaterH
2
O
Very Polar
Covalent
Polyvinyl alcohol(CHCOH)
n
Very polar
covalent
MethanolCH
3
OH
Polar
Covalent
MethaneCH
4
Non‐polar
Covalent
OxygenO
2
Non‐polar
Covalent
‐‐‐ Indicates the compound decomposes into a different compound prior to boiling.
The melting point of magnesium oxide is
2852 ˚C
and the boiling point is
3600 ˚C
. Magnesium oxide is a fine white powder. Describe what you think
you would see happen if you heated a small pile of magnesium oxide to atemperature of 2,853˚C?
The MgO would turn into a liquid at that
temperature.
There are three bond types listed in the table. Are there any patternsbetween the types of bonds and the boiling and melting points? Describe asmany patterns as you can see.
Ionic bonds have very high melting and boiling points, while non‐polarcovalent bonds have very low melting and boiling points. The melting andboiling points of polar covalent bonds are in between ionic and non‐polarcovalent.
Does the amount of charge or the distance between charges have a greaterimpact on the strength of the Coulombic Force?
(Remember that Coulombic force
is just a fancy name for the attraction and repulsion between charged particles.)
The distance between particles plays a larger role in Coulombicattraction than number of charged particles.
Should covalent or ionic bonds be stronger? Explain your reasoning in
terms of the separation (distance between) of the charges.
Covalent bonds should be stronger because the atoms are closertogether and are pulling on one another with more force than ionicbonds.
Model 6: Metallic Bonding ‐ A Fourth Bond TypeRead This! We have seen that two non‐metals tend to share electrons in a covalent bondbecause their electronegativities are so similar. When a metal and non‐metalbond, the large difference in electronegativities typically results in the transferof electrons and the formation of an ionic bond. Metals tend to have similarelectronegativities as other metals.20.
Do you think metallic bonds (bonds between metal atoms) will be more likeionic or covalent bonds? Explain your reasoning.
Answers will vary. This is simply a prediction, so there is no “right” or “wrong”answer
8
Model 4: Explaining the Relative Strength of Ionic Bonds andIntermolecular Forces
Ionic bonds form from the attraction between a (
full / partial
) positive
charge on the cation and (
full / partial
) negative charge on the anion.
Intermolecular forces form (
full / partial
) charges on adjacent molecules.
a.
Which force should be stronger, the intermolecular force (hydrogenbond) or an ionic bond? Explain your reasoning.
Ionic bonds should be stronger because they are formed by the full chargesbetween cations and anions. Model 5: Explaining the Relative Strength of Ionic and CovalentBonds
Typical Ionic Bond
Typical Covalent Bond
How far apart are the ions in a sodium chloride crystal?
282 pm
How far are the hydrogen nuclei from the middle of the shared electrons?
48 pm
Ionic bonds and covalent bonds are really just attractions between positiveand negative charges. How does the distance between the charges of atypical ionic bond compare to the distances in a covalent bond?
There is almost 6 times the distance between the nuclei of ionic bondsthan there is between the nuclei of covalently bonded atoms
Na
+
Cl
‐ Na
+
Cl
282pm ‐
+
+
+
+
+^ +
++ + +
Na
+
Cl
‐
Na
+
Cl
‐
Ionic Bond
+
+
+
+
+^ +
++ + +
Intermolecular force
(hydrogen bond)
Rank the three types of bonds from lowest to highest melting points andthen lowest to highest boiling points.Bonds with lowest
Bonds with highest
melting points
NP colvalent
P covalent
Ionic
melting points
Bonds with lowest
Bonds with highest
boiling points
NP covalent
P covalent
Ionic
boiling points
a.
Explain your rankings in the space below.
The rankings can be explained by the melting and boiling point data in Model2.
