Ch 2 The Chemical Basis of Life Element- substance that can’t be broken down into simpler substances.• # of protons makes each unique
Atom – smallest unit of matter• Composed of:• 1. Protons, +, in nucleus• 2. Neutrons, o, in nucleus• 3. Electrons, -, orbit nucleus in shells or levels http://www.youtube.c om/watch?v=sWVX_ rGzzQU&feature=rel ated Atom animation
Define & distinguish among atomic number, mass number, atomic weight, and valence• Valence is the number of electrons needed to fill the outermost shell of an atom.
Interactions between atoms:• Atoms strive to fill their outer shell w/ e-. To do this they’ll share e- or steal e-• 1st level max of 2• 2nd level – 8
Is this sodium atom satisfied? What could it do?
Compare these twoWhat do you notice is different? How doyou think that would affect its charge? +
Is Chlorine satisfied?What could it do? How do you think that would affect it? -
If I couldonly get rid Heyof this one Sodium,electron in my outer I’ll takeshell I’d be it! I satisfied! need one more to be satisfied!Hey, baby …I + Hey, babysuddenly … I feel the feel this same way.attraction It’s like we have this to you. bond…
Ionic bond – attraction between opp. charged ions• + charged ion – ion with less electrons than protons• - charged ion – ion with more electrons than protons
Covalent bond - atoms share electrons to bond… http://www.wellesley.edu/Biology/Concepts/Html/c ovalentbonding.html
Polar Covalent bond - atoms share electrons unequally to bond…
Molecule- 2 or more atoms that share e-• Represented by formulas• Ex: H2
Unique properties of H2O Bonds b/t the O and H atoms in H2O - polar covalent bond.• Polar covalent bond – unequal sharing of electrons.• Occurs b/c O “hogs” the electrons
Water is polarPolar – one side is +and other side is –Due to O hoggingelectrons.
1. Orgs depend on the cohesion of water molecules.• Cohesion – when H bonds hold a substance together. Contributes to transport of water against gravity in plants. Adhesion – the clinging of one substance to another Ex: Miniscus Surface tension – a measure of how difficult it is to stretch or break surface of a liquid. Due to H bonds Skin
H –bonds make water molecules stick to each other• Weak bonds between water molecules due to its polarity.
Jesus Lizzard• http://www.visionlearning.com/library/mod ule_viewer.php?mid=57&l=&c3=• Link above!
2. Water contributes to Earth’s habitability by moderating temperatures.• It absorbs heat from warmer air & releases heat into cooler air.• Ice cools drinks by absorbing heat• Heat – measure of the total quantity of kinetic E.• Temperature – measure of the intensity of heat due to the average kinetic E of the molecules.Swimmer in ocean has a higher temp than water but the ocean contain far more heat due to its volume.
• Specific heat – amt of heat that must be absorbed or lost for 1 g of that substance to change its temp by 1 C.• measure of how well a substance resists changing its temp.• Water - high specific heat. 1cal/g/C• To increase temp of H2O heat must be absorbed to break H bonds.• To decrease temp of H2O heat must be released to form H bonds. When enough H bonds are formed, it’s solid – ice.• This is why it actually gets a little warmer when the rain turns to snow… heat is released when the H bonds form.
Why is water important to life?3. Cools orgs when they sweat, pant, or roll in mud b/c the hottest molecules are leaving the surface - evaporative cooling.
Why is water important to life?4. Oceans and lakes don’t freeze solid b/c ice is less dense than water so it floats. Less dense b/c when H-bonds form, water molecules are farther apart.
Diffusion• Diffusion = random movement of molecules high concentration to less• Ex: smell of popcorn spreads The Diffusion Applet
Diffusion• Continues until all molecules are evenly spread out.• Dynamic equilibrium = concentration of molecules are even but molecules are still moving.• It’s how molecules get into & out of our cells
Diffusion• The faster the molecules are moving, the faster diffusion will occur.
Why is water important to life?5. Many substances dissolve in it because it is polar.
Terms to know…SoluteSolventHydrophilicHydrophobic
Solute concentration in aqueous solutionsMole – equal in # to the molecular wt. but upscaled to gramsMolecular wt – sum of wts of all atoms in a moleculeSo… to obtain 1 mol of sucrose (C12H22O11):C = 12 (daltons) x 12 (atoms present) = 144H = 1 x 22 = 22O = 16 x 11 = 176Molecular wt = 342 g
molarity• # of moles of solute per liter of solutionSo… to make a 1 molar solution of sucrose you would add 1 liter of water to 342g of sucroseA 0.2 molar solution of sucrose?Add 1 liter of water to 68.4g of sucrose (342 x 0.2)
Orgs are sensitive to changes in pHAcid – substance that increases the H+ of a solutionBase – substance that reduces the H+ of a solution & has more OH- ions.
pH scale• In any solution the product of the H+ and OH- is 10-14• from 0-14 used to show H+ concentrations• Each pH unit represents a tenfold diff in the concentration of H+• pH declines as H+ increases