Opposites Attract Using Chemistry to Explain Biology Atoms ● ● ● ● ● a - not tom - to cut a + tom = not cuttable Basic units of all matter Made up: o Neutron = neutral o Proton = positive o Electron = negative ● Electrons and protons are attracted to each other... ● But electrons move too much to join the protons in the nucleus Atoms ● When... o there are equal numbers of protons and electrons = no charge o there are more protons than electrons = positive charge o there are less protons than electrons = negative charge ● If an atom has a charge, called ion Compounds ● When two or more atoms (elements) bond to each other ● Compounds properties are very different from individual atoms ● Ex) Na + Cl = Salt https://www.youtube.com/watch?v=ODf_sPexS2Q https://www.youtube.com/watch?v=aK85PZX2xNE Compounds ● Created using bonds ● Three types of bonds... Ionic Bonds (The Taker and the Giver) ● ● ● ● ● Electron is transferred from one atom to the other atom One atom adds an electron and gains a negative charge One atom loses an electron and gains a positive charge Since the atoms are charged, they are ions Ex) Salt = NaCl o Na loses electron o Cl gains electron Covalent Bonds (The sharers) ● Neither atom has enough electrons ● Atoms share electrons ● Ex) Carbon dioxide Van der Waals Forces ● ● ● ● ● ● (The Stickers) Weakest of three bonds Covalent bonds don’t always share equally Some atoms attract electrons more than others When molecules close together, creates attraction “Sticky” Ex) Water, H2O o Electrons more attracted to oxygen (O) and stay near it more o Oxygen slightly more negative than hydrogen (H) Bonding Activity ● Form groups of four (student choice) ● Pretend you are all atoms trying to become compounds ● Create a simulation for all three types of bonds o Ionic o Covalent o Van der Waals ● When you are ready, come to Ms. Crocker. She will pick a bond for your group to act out Water - The Most Important Compound Most abundant Compound in all life ● Many unique properties make it suited to support life o Polarity o Hydrogen Bonds o Solubility o High specific heat capacity ● Polarity ● Caused by Van der waals forces ● Creates hydrogen bonds in H2O o Slightly negative O is attracted to slightly positive H ● Hydrogen bonds create cohesion and adhesion Hydrogen Bonds - Cohesion ● Slight charge of water molecules attract other water molecules http://www.youtube.com/watch?v=45yabrnryXk&t=0m46s Hydrogen Bonds - Adhesion ● Slight charge in water molecules makes it stick to other types of molecules Solubility ● Polarity means it can break apart ionic and polar molecules ● Ex) Salt Water o Negative Cl surrounded by positive H o Positive Na surrounded by negative O ● Nonpolar molecules stay separate o Ex) Oil (nonpolar) and Water (polar) do not mix ● Important for many characteristics of life o Ex) Dissolves solids in our body to be carried in our blood High Specific Heat Capacity ● Water needs a lot of energy to raise by 1 degree o Water is “sticky” due to cohesion, so needs more energy ● Helps to maintain an important characteristic of life - homeostasis ● Homeostasis maintains internal conditions like temperature, nutrient levels, and water content ● High water content means our temperatures don’t change easily Properties of Water Worksheet ● Working individually or in pairs with the person sitting next to you, fill out the worksheet ● We will discuss this in class ● Be prepared to share your answers Acids and Bases ● Water is constantly reacting (breaking apart) to form ions (charged molecules) o H2O → H+ & OH- (Ions - Broken apart) o H+ & OH- → H2O (Neutral - Reformed) ● In pure water - 1 in 550 million water molecules are ions pH Scale ● ● ● ● ● Measures H+ ions in a solution On a scale from 0 to 14 More H+ is lower on the scale 7 is neutral Logarithmic scale (something with a ph of 1 has 10x more H+ atoms than something with a pH of 2) pH Indicators ● Tests the amount of free H+ ions in a solution ● Will change different colors depending on the pH level of a solution ● Ex) Bromothymol Blue o http://www.youtube.com/watch?v=opsNV4VqAbk Acids ● Chemicals that contain more H+ than pure water ● More H+ than OH● pH is below seven ● Strong acids have a pH of 0-2 Bases ● Chemicals that contain less H+ than pure water ● Less H+ than OH● pH greater than 7 ● Strong bases have a pH of 11-14 Turn and Talk ● Why do you think strong acids and strong bases are so corrosive (damaging, can cause burns)? Turn and Talk ● What do you think happens when you mix a strong acid and a strong base? Buffers ● To maintain homeostasis, the body needs to maintain fluids between pH of 6.5 and 7.5 ● Uses buffers o can either be a weak acid or base (close in pH to the neutral of 7) o in presence of strong acid, acts as weak base to accept extra H+ o in presence of strong base, acts as weak acid to accept OHo reduces rapid pH changes ● Ex) Bicarbonate molecules in blood (HCO3-) pH Practice ● In your notes, identify the following as acid or base o Human Blood - 7.4 o Rain - 5.6 o Bleach - 12.6 o Stomach Acid - 1.5 o Battery Acid - 0 o Urine - 6 o Seawater - 8 ● Identify the strongest acid and strongest base ● Identify the weakest acid and weakest base