1.3 Atoms and the Properties of Water

Notes

Living things are built mostly from the elements carbon, hydrogen, oxygen, nitrogen, phosphorus and sulfur. Water ($\text{H}_2\text{O}$) is the most common molecule in cells.

• Water is polar: oxygen pulls electrons more, so it is slightly negative and the hydrogens are slightly positive.
• Polar molecules form hydrogen bonds with each other.
• Cohesion: water sticks to water (surface tension). Adhesion: water sticks to other surfaces (water climbing a paper towel).
• Water has a high specific heat, so it resists temperature change.
• Ice is less dense than liquid water, so it floats and insulates lakes.
• Water is a great solvent for other polar and charged substances.
• The pH scale runs 0 to 14: below 7 is acidic, 7 is neutral, above 7 is basic.