Biology 12 Name: KEY Cell Compounds, Bonds, Reactions - 1 Order of Subtopics Covered: 1. Chemical Bonds a. Ionic b. Covalent 2. Water a. Hydrogen Bonds b. Importance 3. Acids & Bases a. ph b. Buffers 4. Synthesis & Hydrolysis Chemical Bonds Compound: 2 or more ELEMENTS joined by CHEMICAL bonds. Chemical Bond: The ATTRACTIVE force that holds atoms together. Chemical Compounds Bond Type ph Organic/inorganic Ionic Covalent IONIC BOND: OPPOSITELY charged atoms (IONS) are attracted to each other. o About Ionic bonds: - Are relatively WEAK in biological systems - Ionic bonds readily DISSOLVE in water. - Very important examples are ACIDS and BASES.
What Happens 1) Atoms without full outer electron orbits aren t STABLE Recall that 1 st shell 2 e - 2 nd shell 8 e - 3 rd shell 8 e - 2) Neutral atoms GAIN electrons (metal) or LOSE electrons (non-metal); ions are more STABLE than neutral atoms. What it looks like 3) OPPOSITELY charged ions are attracted to each other; this is what forms the BOND COVALENT BOND: 2 or more atoms SHARE electrons equally (non-polar compound) or somewhat ASYMMETRICALLY (polar Compound). o About Covalent Bonds: - Happen between 2 NON-METALS - Are STRONG Bonds - Usually form GASES or LIQUIDS at room temp. - CARBON bonds covalently (organic compounds). What Happens 1) Atoms without full outer electron orbits aren t stable. Recall that 1 st shell 2 e - 2 nd shell 8 e - 3 rd shell 8 e - What it looks like 2) When combined, unstable NEUTRAL atoms will SHARE atoms to complete their outter shell.
o ELECTRON pairs that are involved in bonds spend time around BOTH ELEMENTS involved in bonding. - if equal compounds are NON-POLAR (Eg. F2) and DON T carry a charge. - if NOT EQUAL compounds are polar (Eg. H2O) and carry a charge. It is this unique property of water molecules that allows ionic compounds to disassociate (break apart easily in water) or allows for cohesion (sticking together)of water droplets. Water HYDROGEN BOND: HYDROGEN atom is shared between 2 ELECTRONEGATIVE atoms o One oxygen atoms ionically bonded to it & another oxygen atom from another water molecule. THE IMPORTANCE OF WATER (H2O): o o Is polar, & forms H-BONDS SO it can: 1) Act as SOLVENT for POLAR molecules UNIVERSAL solvent
2) Regulates TEMPERATURE 3) Acts as a LUBRICANT 4) Causes cohesion between water molecules results in SURFACE TENSION. 5) Causes HYDROPHOBIC INTERACTIONS because water molecules are polar. SO, compounds that are NON-POLAR will collect together in an effort to stay away from water - Eg. Oil is non-polar and doesn t mix with water. Acids and Bases ACIDS & BASES Acids are IONIC compounds & DISSOCIATE in water, releasing H + o eg. HCl Bases are IONIC compounds & dissociate in water, releasing OH - o eg. NaOH The STRENGTH of an acid or base depends on how well the ions dissociate in water. o HCl is STRONG and the H + and Cl - will almost COMPLETELY dissociate when placed in water. o CH3COOH is WEAK and the amount of CH3COO - and H + produced when placed in water is LOW. ph is the scale used to measure the ACIDITY; ph indicates the [H + ] o ph 1 = [H+] 10-1 ph 10 = [H+] 10-10 o difference of 1 unit is a 10 fold difference in ACIDITY and [H+]. - ph = 2 vs. ph = 4 100 fold difference in [H + ] (10 x 10) 0 1 2 3 4 5 6 7 8 9 10 11
BUFFERS: can accept EXCESS H + or OH - from a SOLUTION, thus removing freefloating H + or OH - from solution. can maintain relatively CONSTANT ph (to a limit) buffers do not CHANGE ph, but do help to keep it CONSTANT. Main buffers in biological systems: 1) Bicarbonate (HCO3) 2) Phosphates Synthesis and Hydrolysis 3) PROTEINS (most important buffers) Biological chemical reactions work OPPOSITE of each other. synthesis means TO PUT TOGETHER o 2 Names: CONDENSATION reaction, or DEHYDRATION synthesis o 2 molecules join by the REMOVAL of OH group from one and an H atom from the other water (H2O) hydrolysis means TO SPLIT WITH WATER o REVERSE of synthesis. o Organic molecules are HYDROLYZED into simpler building blocks by the addition of the EQUIVALENT of a water molecule. polymer means A LARGE MOLECULE MADE UP OF REPEATING SUBUNITS (MONOMERS) H2O H OH