Chemistry of Life Chapter 3 Biology Mr. Gilbertson

Atoms n Smallest particle of matter which still retains the property of that material. n Made up of smaller particles n Mostly made up of empty space n So small that they cannot be seen even with the most powerful microscopes n Atoms an element are unique to that element but similar to all other atoms of that element

Elements n Any material that is made up of only one kind of atom n Examples: iron, carbon, gold, oxygen, lead, silver, etc. n There are 90 naturally occurring elements n 13 are man made n Total 103 elements listed n Each is represented by an atomic symbol

CHEMICAL BONDING n All atoms need to have a full outer energy level, filled with electrons to be stable. (for most 8 electrons) n Atoms with less than a full outer energy level will react (lose, gain, or share electrons) with other atoms, to fill the outer energy level and become stable.

COVALENT BONDS n When two or more atoms share electrons to form a molecule n A molecule is a group of atoms held together by covalent bonds n All organic molecules are covalently bonded and made up of molecules (molecular) n Normally the number of electrons and protons is the same in a molecule so they are usually neutral in terms of charge. n Sometimes the electrons are more strongly attracted to one end of a molecule, it is said to be polar

HYDROGEN BONDING n Electrons are shared between atoms, but sometimes they are more attracted to one of the bonded atoms than the other. n This forms a slight difference in charge from one end of a molecule (H 2 O) to the other. n It is said to have poles, or to be polar n Allows molecules to attract one another, opposite charges attract, like charges repel n Called hydrogen bonding – weak form of chemical bonding

IONIC BONDING n Ions are atoms that are charged due to a loss or gain of electrons n Atoms with less than three electrons in the outer energy level tend to lose electrons (they form positive ions) n Atoms with five or more electrons tend to gain electrons (they form negative ions) n When two oppositely charged ions are attracted to one another (one positive and one negative) an ionic bond is formed. n The bond between sodium (Na) and chlorine (Cl) is an ionic bond.

WATER MOST IMPORTANT MOLECULE TO LIFE n n INORGANIC MOLECULE n n UNIQUE PROPERTIES POLAR MOLECULE EFFECTIVE SOLVENT STRONG ADHESION STRONG COHESION RESULTS IN CAPILLARY MOVEMENT HIGH SPECIFIC HEAT

COHESION OF WATER O H H O H H O H H O H H O H H O H H O H H O H H O H H O H H O H H O H H O H H O H H O H H WATER FORMS AN ORGANIZED PATTERN OF MOLECULES ALL OF WHICH ARE ATTRACTED TO EACH OTHER

COHESION OF WATER n Caused by hydrogen bonding n Cohesion refers to the attraction between molecules of the same substance n Enables water to form a thin film or a drop n Molecules at the surface are linked tightly so they form a “skin” known as surface tension n Surface tension prevents water surface from stretching or breaking easily. n Requires more energy to evaporate.

ADHESION OF WATER n The attraction of molecules of different substances n Water is attracted to solid surfaces. n Causes some surfaces to get “wet” n Adhesion powers the process of capillary action in which water moves upward in narrow tubes such as plant stems n The attraction due to adhesion is stronger than the force of gravity so the water “climbs” the tube. (Max height is 32ft or 9.8m)

High Specific Heat of Water n Water absorbs heat more slowly than other substances n Organisms are able to get rid of excess heat by evaporation of water (sweat) n Enables organisms to maintain a constant temperature even in a changing environment. n Helps maintain homeostasis

AQUEOUS SOLUTIONS n Water is called the universal solvent n Almost anything will dissolve in water to some extent n A solution is a mixture in which one or more substances are uniformly distributed in another (kool-aid) n Many important substances in the body are dissolved in blood or other body fluids n Any solution in which one of the components is water is said to be an aqueous solution. n Aids in transportation of materials within cells and within organisms

POLARITY OF WATER O H H THE POLARITY OF WATER IS CAUSED BY THE UNEQUAL DISTRIBUTION OF ELECTRONS, SINCE THE ELECTRONS STAY WITH THE OXYGEN IT TENDS TO HAVE A SLIGHTLY NEGATIVE CHARGE

POLARITY OF WATER n Enables water to dissolve a great number of organic compounds (polar molecules) n Enables water to dissolve ionic compounds (mineral ions) n Nonpolar molecules do not dissolve well in water they tend to clump. n The nonpolar cell membrane tends to form a boundary past which polar water molecules cannot easily pass.

ACIDS AND BASES n In water there are some molecules which will dissociate into ions H + (Hydronium ion) and OH - (Hydroxide ion) n Any solution which produces a higher than normal concentration of H + ions is called an Acid n Any solution which produces a higher concentration of (OH - ) ions is a base or alkaline solution. n pH is a measure of the inverse H + ion concentration n A pH of 7 is neutral, a pH of less than 7 is acid, and a pH greater than 7 is a Base n If you add an acid and a base they will neutralize