CHEMISTRY AND LIFE Characteristics of life is highly organized compared to inanimate objects can assimilate and use energy can respond to the environment can reproduce through use of the information encoded in DNA is composed of one or more cells Atoms invisible and indivisible cannot be further reduced through chemical reactions Sub particles protons neutrons electrons cannot exist by themselves as matter Most of atomic weight resides in nucleus What makes the elements different from each other Atomic Number Number of protons Proton number is primarily responsible for the chemical characteristic of the atom Neutrons add weight not identity to an atom Isotope an atom with greater or fewer neutrons Carbon 14 Carbon with 8 neutrons Atoms seek stability Electrons reside in defined energy levels around nucleus Number of electrons in outermost shell determine the atom s reactivityMolecule bonded atoms Three types of chemical bonds 1 Covalent Bonds strongest of the three bond types involves a sharing of electrons between atoms Polar covalent molecules electrons are shared unequally between atoms resulting in a molecule with slightly positive and negative ends Nonpolar covalent molecules electrons are shared equally molecule has no positive or negative end 2 Ionic Bonds Ions are atoms with greater or fewer electrons Compare covalent molecules have a fixed number of atoms ionic compounds do not 3 Hydrogen bonds an attraction of opposite charges individually weak collectively strong Hydrophilic reacts with water Hydrophobic does not react with water Water Unique characteristics less dense as a solid high heat capacity high cohesion universal solvent Acids and Bases Measured on pH scale concentration of hydrogen ions pH scale is logarithmic Acid donates hydrogen ions Base accepts hydrogen ions Carbon Carbon starting point for all important biological molecules can form four covalent bonds basis of hydrocarbon backbones Double bonds rigidify molecules Macromolecules Macromolecules are those that are constructed on a monomer polymer concept Monomer a single molecular building block Polymer three or more monomer units bonded together Water is formed when polymers are made condensation reaction water must be present to break down polymers Carbohydrates Three to get familiar with glucose ribose deoxyribose Glycogen how animals store energy Starch how plants store energy Cellulose a structural molecule Branching glycogen is more highly branched than starch Cellulose is unbranched hydrogen bonding between strands keeps water out
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