Chapter 2.2: Hydrogen Bonds
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22 Terms
What is a hydrogen bond?
A weak, non covalent attraction between a partially positive hydrogen and an electronegative atom
What type of interaction is a hydrogen bond?
A special type of dipole-dipole interaction
When does hydrogen bonding occur?
When hydrogen is covalently bonded to a highly electronegative atom, usually oxygen or nitrogen
Why does hydrogen become partially positive in a hydrogen bond?
The electronegative atom pulls the bonding electrons toward itself, leaving H with a partial positive charge (δ⁺)
What attracts the partially positive hydrogen?
An unshared pair of electrons on another electronegative atom
Hydrogen bond acceptor
The electronegative atom that provides an unshared pair of electrons for the hydrogen bonds
When is a hydrogen bond strongest?
When the three atoms involved are arranged in a straight line
How many hydrogen bonds can one water molecule form?
Four
How does water form 4 hydrogen bonds?
It can donate 2 through its hydrogen atoms and accept 2 through oxygens unshared electron pairs
What happens to hydrogen bonds in liquid water?
They constantly break and reform
How are hydrogen bonds different in ice?
They form a more stable, organized structure
How many other water molecules can each H2O bond to in ice?
Four
Why does ice float?
Ice is less dense than liquid water
What happens to water when it freezes?
It expands instead of contracting
How strong are hydrogen bonds compared with covalent bonds?
Hydrogen bonds are much weaker than covalent bonds
Why can weak hydrogen bonds still have a major effect on water?
Water molecules form many hydrogen bonds, and their combined effect strongly influences water’s properties
What properties of water are affected by hydrogen bonding?
Its melting point, boiling point, and density
What types of molecules can form hydrogen bond with water?
Alcohols, amines, carboxylic acids, esters, aldehydes, and ketones
Why are hydrogen bonds important in biology?
They help stabilize the structures of DNA, RNA, and proteins
How do hydrogen bonds help DNA?
They connect complementary bases and help stabilize the DNA double helix
How do hydrogen bonds help proteins?
They help form and stabilize α-helices and B-pleated sheets