4.1: Question 4.E.20 PASS - which is the most polar bond?
- Page ID
- 452248
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Which is the most polar bond?
C–C
C–H
N–H
O–H
Se–H
- Answer
-
O-H is the most polar bond.
See LibreText 4.3 Covalent Bonding (section 4.3.3 Electronegativity)
- Strategy Map
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Step Hint 1. Assign your electronegativity values to each atom (use Pauling Electronegativity values from figure 4.3.3 of the LibreText). Recall electronegativity represents the tendency of an atom to attract electron density (see LibreText section 4.3.3) 2. Identify the electronegativity difference between the elements forming the bond. To do this, subtract the larger value from the smaller value.
3. Identify which bond has the largest electronegativity difference, that will be the most polar bond.
- Solution
-
C–C
Electronegativity difference = 0
C–H
C electronegativity = 2.5, H electronegativity = 2.1
Electronegativity difference = 0.4
N–H
N electronegativity = 3.0, H electronegativity = 2.1
Electronegativity difference = 0.9
O–H
O electronegativity = 3.5, H electronegativity = 2.1
Electronegativity difference = 1.4
Se–H
Se electronegativity = 2.4, H electronegativity = 2.1
Electronegativity difference = 0.3
O-H has the largest electronegativity difference so it is the most polar bond.
- Guided Solution
-
Download Guided Solution as a pdf
Guided Solution Hint This is a theory type problem that asks us to evaluate the covalent bonds between the elements given. We are asked to determine the most polar bond, which will be the bond with the most unequal electron distribution. See LibreText 4.3 Covalent Bonding (section 4.3.3 Electronegativity) Which is the most polar bond?
C–C
C–H
N–H
O–H
Se–H
The question asks you to identify which of the given bonds is the most polar, what property could relate to this? Electronegativity is a measure of the tendency of an atom to attract electrons or electron density. Which bond has the highest electronegativity difference? Recall that polar covalent bonds have an electronegativity difference between the electron sharing atoms. For this type of bond to occur the difference guideline is between 0.4 and 1.8. Within this range, the higher the difference, the more polar the bond.
See LibreText 4.3 Covalent Bonding (section 4.3.5 Electronegativity and Bond Type)
Complete Solution:
C–C
Same element type, no electronegativity difference so the bond is nonpolar.
C–H
C electronegativity = 2.5, H electronegativity = 2.
Electronegativity difference = 0.4
N–H
N electronegativity = 3.0, H electronegativity = 2.1
Electronegativity difference = 0.9
O–H
O electronegativity = 3.5, H electronegativity = 2.1
Electronegativity difference = 1.4
Se–H
Se electronegativity = 2.4, H electronegativity = 2.1
Electronegativity difference = 0.3
Difference less than 0.4 so the bond is nonpolar.
The bond with the highest electronegativity difference is between O and H, therefore it is the most polar bond.
Answer: O-H
For all bonds except C-C one of the atoms is H, so you can focus on the change in electronegativity of the atom H is bound to.
If you rank these atoms from highest to lowest electronegativity you will predict which bond with H will be the most polar.
Check your work!
The most electronegative atom bound to H above is O with an electronegativity of 3.5, so we would predict that O-H would be the most polar bond in the list.
Why does this answer make chemical sense?
The more electronegative an atom is, the stronger the attraction between its nucleus and outside electrons will be. Atoms that are smaller will have higher electronegativities as there are fewer electrons to shield the nucleus from this attraction. Oxygen is one of the most highly electronegative elements as its nucleus forms a very strong attraction to outside electrons such as with a hydrogen atom.
Electronegativity ranking from largest to smallest:
O > N > Se > C
(question source from page titled 7.E: Chemical Bonding and Molecular Geometry (Exercises) https://chem.libretexts.org/Bookshelves/General_Chemistry/Chemistry_1e_(OpenSTAX)/07%3A_Chemical_Bonding_and_Molecular_Geometry/7.E%3A_Chemical_Bonding_and_Molecular_Geometry_(Exercises), shared under a CC BY 4.0 license, authored, remixed, and/or curated by OpenStax, original source https://openstax.org/books/chemistry-2e/pages/7-exercises, Access for free at https://openstax.org/books/chemistry/pages/1-introduction)