Warm-Up: Drops On A Penny Complete the mini-lab on your desk. Write your answers on the paper provided and glue sideways into your composition book.

Biology Notes Biology & Biochemistry Part 3 Pages 40-43

How do the unique properties of water allow life to exist on Earth? Standard ____ Discuss the properties of water that contribute to Earth’s suitability as an environment for life: cohesive behavior, expansion upon freezing, and versatility as a solvent Essential Question 2.1 How do the unique properties of water allow life to exist on Earth?

I. Water Water is a molecule which means its atoms __________ electrons This makes water a _____________ molecule In water, there is one atom of ___________ and two atoms of __________ share covalent oxygen hydrogen

Remember….. Compounds are made of atoms. Water has 3 atoms total. This makes water a compound. We know that the atoms share electrons but WHY??????? Compounds are formed so that atoms can get full outer energy shells What is a full outer energy shell? 2 electrons on the first shell 8 electrons on the second shell

Although the electrons in water are _________, they are not shared _________ between the oxygen atom and the ____ hydrogen atoms polar molecule = a group of atoms that __________ electrons unequally resulting in charges on the atoms water is a _______ covalent molecule shared equally 2 share polar

Due to it’s polarity, (unequal sharing of electrons) the oxygen atom in water has a small ________ charge and each of the hydrogen atoms has a small __________ charge negative positive

Drawing of water as a polar covalent molecule:

The charges on a water __________ allow it to be attracted to and ________ with other water molecules Hydrogen Bond = the bond that forms between hydrogen and another ________ covalent molecule hydrogen bonds are considered to be very ______ and not nearly as strong as __________ or ionic bonds molecule bond polar weak covalent

Water’s _________ and the resulting __________ bonds that water can form with itself as well as other _______ covalent molecules allows water to have very special _________ These properties explain why water is important to _______ on _______ polarity hydrogen polar properties life Earth

II. The Properties Of Water Water is cohesive Cohesion = an attraction between ___________ of the same substance water is attracted and ______ to itself with weak __________ bonds e.g. molecules bonds hydrogen water droplets, dew

B. Water has surface tension Surface Tension = in bodies of water, the inward _____ of water molecules caused by _________ surface tension is the reason why certain bugs can ________ on water pull cohesion walk

Drawing of surface tension in a pond or lake:

Think about it…… Why do oceans not exhibit surface tension? Imagine we are all form a circle and have a sheet pulled tight on the edge. Still holding on we lean back. What happens if one person lets go? Oceans do not exhibit surface tension because of currents, wind, and objects that break the hydrogen bonds between the water molecules.

different polar C. Water is adhesive Adhesion = an attraction between molecules of __________ substances water is attracted to other ______ molecules different polar

Drawing of water in a glass showing adhesion:

D. Water can move by capillary action Capillary Action = the ability of water to move ___ thin tubes even defying _________ capillary action is due to ___________ e.g. up gravity adhesion xylem in trees, paper towels

sugar water / salt water E. Water is a universal solvent Solution = a mixture of two or more ____________ in which molecules are distributed _________ i.e. Solvent = the substance in which the solute __________ Due to water’s _________, solutes that are also ________ are attracted to water and tend to break apart and become surrounded by the _________ e.g. substances evenly sugar water / salt water dissolves polarity polar water see page 42

In the body, water is valuable as a solvent water dissolves ( _________ ________ ) the foods we eat breaks apart

Going back to oceans…. Another reason why oceans do not display surface tension is because of the salt….WHY? Water is attracted to the salt more than itself so it’s water is less cohesive to itself. Without cohesion, there can be no surface tension.

F. Water has a high heat of vaporization Heat of vaporization = the amount of _____ it takes for a substance to ___________ it takes a large amount of heat to _______ the hydrogen bonds between water molecules heat evaporate break

sweat body evaporate homeostasis this is valuable in the human body in the form of _______ when we exercise, heat accumulates in the _______ the heat is used to ___________ the water in the body sweat results and _____________ is maintained for body temperature sweat body evaporate homeostasis

G. Water expands when frozen

III. Acids, Bases & pH In some instances, when water is used to dissolve substances, some of the water molecules will break down to form ions (ion = an atom/compound that has gained or lost an electron forming an electrical charge on the atom/compound)

H2O → OH- + H+ H+ OH- Breakdown of water molecules to form ions: ____ = Hydrogen ion _____ = Hydroxide ion We can determine how ______ or ______ a substance is by measuring the amount of __________ ions formed when that substance is dissolved in water H2O → OH- + H+ H+ OH- acidic basic hydrogen

distilled (pure) water pH (potential of hydrogen) = the concentration (strength of amount) of ___ ions in solution (when the substance is dissolved in ______) pH is measured of a sale of _________ A pH of ____ is considered neutral A neutral solution is one that has an equal amount of ____ ions and ____ ions e.g. H+ water 0 - 14 7 OH- H+ distilled (pure) water

H+ acid = a substance that forms ____ in solution and has a pH of ______ this means there are more ____ ions than ______ ions e.g. 0 - 6 H+ OH- acid rain tomato juice stomach acid

base = a compound that forms ____ in solution and has a pH of ______ This means there are more ____ ions than ____ ions e.g. OH- 8-14 OH- H+ alkaline batteries detergents blood

In the human body a pH between ___ and ___ must be maintained as part of _____________ buffer = a substance used to help __________ pH within the body e.g. 6.5 7.5 homeostasis maintain Tums, calcium, pepcid AC, milk of magnesia