Water is essential to life as we know it. Its molecular structure gives it properties that influence the chemistry of cells and the environments where organisms live.
A water molecule, H₂O, contains two hydrogen atoms joined to one oxygen atom by polar covalent bonds. Oxygen is more electronegative than hydrogen, so it attracts the shared electrons more strongly. This creates a slightly negative region near oxygen and slightly positive regions near the hydrogen atoms. The molecule has no overall charge, but its charges are unevenly distributed, making water polar.
All flashcards
What makes water a polar molecule?
Oxygen attracts shared electrons more strongly than hydrogen, creating a slightly negative oxygen region and slightly positive hydrogen regions. The molecule is neutral overall but has an uneven charge distribution.
What is a hydrogen bond?
It is an attraction between a partially positive hydrogen region in one molecule and a partially negative region, often oxygen, in another molecule.
What do hydrophilic and hydrophobic mean?
Hydrophilic substances interact readily with or dissolve in water. Hydrophobic substances, such as oils, do not interact readily with water.
Why is ice less dense than liquid water?
Hydrogen bonds hold water molecules in a crystalline arrangement with more space between molecules than in liquid water.
How does pond ice support aquatic life?
Because ice floats, it forms a surface layer that slows heat loss from the water below.
Quiz questions
Why does an oxygen atom in water carry a partial negative charge?Answer: Oxygen attracts the shared electrons more strongly than hydrogen does.
What is a hydrogen bond between water molecules?Answer: An attraction between a partially positive hydrogen region and a partially negative oxygen region.
Which substance is most likely to be hydrophobic?Answer: A nonpolar oil.
Why does ice float on liquid water?Answer: Hydrogen bonds hold frozen water molecules farther apart, making ice less dense.
How can floating ice help organisms in a pond during winter?Answer: The surface ice acts as insulation and slows the cooling of water below it.
Based on Biology 2e by Mary Ann Clark, Matthew Douglas, Jung Choi (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.