Do Now Describe and draw a picture of a ionic bond Describe and draw a picture of a covalent bond
KEY CONCEPT Water’s unique properties allow life to exist on Earth.
Life depends on hydrogen bonds in water. Water is a polar molecule. Polar molecules have slightly charged regions, due to uneven pull on electrons. O H _ + Nonpolar molecules do not have charged regions. Hydrogen bonds form between slightly positive hydrogen atoms and slightly negative atoms.
Hydrogen bonds are responsible for three important properties of water. high specific heat cohesion adhesion
Properties of water related to hydrogen bonds High Specific Heat - Large amount of energy needed to produce an increase in temperature. Important in regulating temperature of cells Cohesion - water molecules “stick” to each other Beads of water Surface tension Adhesion - water molecules “stick” to other substances Helps transport water from roots to leaves in plants
Many compounds dissolve in water. A solution is formed when one substance dissolves in another. A solution is a homogeneous mixture. Solvents dissolve other substances (greater concentration). Solutes dissolve in a solvent (lower concentration). solution
Do NOW What does “like dissolves like” mean?
“Like dissolves like.” Polar solvents dissolve polar solutes. Nonpolar solvents dissolve nonpolar solutes. Polar substances and nonpolar substances generally remain separate. Oil and Water
Acids and Bases Acids taste sour, are corrosive to metals, change litmus (a dye extracted from lichens) red, and become less acidic when mixed with bases. Bases feel slippery, change litmus blue, and become less basic when mixed with acids.
Some compounds form acids or bases. An acid releases a hydrogen ion when it dissolves in water. high H+ concentration pH less than 7 more acidic stomach acid pH between 1 and 3
A base removes hydrogen ions from a solution. low H+ concentration pH greater than 7 bile pH between 8 and 9 more basic
A neutral solution has a pH of 7. pure water pH 7
How do Acids and Bases work? Water can dissolve compounds into their individual ions Acids Compounds that contain hydrogen and release a hydrogen ion when put in an aqueous (water) solution Bases Substances that dissolve in water and release hydroxide ions (OH-) into solution. Neutralization acids release H+ into solution and bases release OH-. If we were to mix an acid and base together, the H+ ion would combine with the OH- ion to make the molecule H2O, or plain water Always produces water and a salt