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Chapter 2


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BIOL 102
Peter T Boag

BIOL 102 Chapter 2: Chemical Basis of Life 2.1 Atoms *see hand written note 2.2 Chemical Bonds that Create and Stabilize Molecules Molecular formula: given formula for any molecule (ex. Oxygen: O , G2ucose: C H O6)12 6 Compound: molecule made of two or more different elements (ex. Carbon AND Oxygen: CO ) 2 Covalent Bond: a bond in which atoms share a pair of electrons if their outer shell is not full; this bond is strong, as the electrons act as if they belong to both atoms  Each element has a characteristic number of covalent bonds it can form with other atoms depending on the amount of valence electrons it has  Double bonds occur when the atoms share two pairs of electrons rather than one pair  Some atoms attract shared electrons more readily than others Electronegativity: the measure of an atom’s ability to attract electrons in a bond; Polar Covalent Bond: a covalent bond in which an electron’s orbit is closer to the atom with a higher electronegativity than the atom with lower electronegativity (skewed distribution of electrons) Polar Molecule or “Dipole”: Molecule whose atoms are bonded with a polar covalent bond (ex. H O – 2 electrons are closer to Oxygen than either Hydrogen; this gives H O2a region of partial negative charge and two regions of partial positive charge) Nonpolar Molecule: Molecule whose atoms are bonded with a nonpolar bond (ex. C or CH a2e 2 electrically neutral/nonpolar, as the electronegativity of Carbon is relatively similar to that of Hydrogen)  It is common for large molecules to have both polar and nonpolar bonds (ex. Detergent – nonpolar ends dissolve in skin oils, polar ends allow detergent to rinse off in water)  Hydrogen, Oxygen, Nitrogen, and Carbon are the most abundant elements in living organisms. Atoms are electrically neutral because of their equal number of electrons and protons. Ion: and atom with a positive or negative charge due to a lost (positive charge) or gained (negative charge) electron.  Some ions become more stable with the loss or addition of an electron (ex. Na has one electron on its valence shell, therefore it loses its third energy shell has a full valence shell when it loses one electron) Ionic Bond: occurs when a cation binds to an anion through the transfer of an electron Free Radical: a molecule containing a single unpaired electron in its outer energy shell  Free radicals can react with other molecules to steal electrons from one of their atoms, filling the orbital in the free radical; this process creates a free radical in the donor molecule, setting off a chain reaction  CON* Free radicals can be very harmful to living cells, as it causes rupturing to the cell membrane or genetic material  PRO* Free radicals in animals’ bodies may be used to kill invading bacteria  Free radicals in organisms need to be inactivated so they do not kill healthy cells; they need molecules that can donate electrons without becoming highly reactive (ex. Vitamins in fruits and vegetables contain flavonoids, which prevent reactivity and protect molecules; beneficial to health) Chemical Reaction: occurs when one or more substances/compounds are changed into other substances/compounds; when compounds breakdown into molecules; when electrons are added/taken from an atom  Source of energy (heat) is required for molecules to encounter each other in a chemical reaction  Heat is necessary in a chemical reaction for atoms/molecules to vibrate and move (Brownian motion); if not, temperature is “absolute zero”, which means atoms/molecules are stationary/unable to interact  Eventually reach equilibrium state  Chemical reactions in organisms occur in water environments Chemical Equilibrium: forward reaction rate is balanced by reverse reaction rate (when all reactants are converted to products) Catalyst: Substance that speeds up
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