BIOL 150 1st Edition Chemistry Background continued Lecture 4 H O H Ol H H ClCl Na Cl Na ClCovalent bonds Ionic interactions Hydrogen bonds DNA is held together tightly by Hydrogen bonds Properties of atoms that form molecules less than 4 tend to lose electrons these will have more protons than electrons and will be positively charged ions 4 or more tend to share electrons 7 electrons tend to gain electrons These will have fewer protons than electrons and will be negatively charged ions What is an ion In sodium chloride salt sodium loses an electron and becomes positively charged and chlorine gains an electron and becomes negatively charged The two ions are attracted to each other Sodium chloride NaCl dissolves in solution because the sodium Na ions and chloride Cl ions each become surrounded by water molecules Water and Hydrogen bonds Collectively hydrogen bonds hold water molecules together a phenomenon called cohesion Cohesion also helps the transport of water against gravity in plants Water has a high specific heat it can absorb heat before changing its temperature HEAT is absorbed when hydrogen bonds break HEAT is released when hydrogen bonds form Ice floats because it is less dense than liquid water WHY Why don t most ponds or lakes freeze solid in cold winters These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Water and Hydrogen Bonds Molecules that can interact with water molecules ex molecules in the bloodstream or the soluble cytoplasm of a cell are hydrophilic molecules Molecules that do NOT interact with water molecules ex fatty acids lipids or proteins that will be found in membranes are hydrophobic molecules Example H H l H C OH O l H H Methane