General Biology I- Txtbk Ch 2
General Biology I- Txtbk Ch 2
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Date Created: 07/09/14
The Chemical Context of Life Monolay July 7 ZQJ14 221 PM 21 Matter Consists of Elements and Compounds Matter anything that takes up space and has mass Elements and Compounds 0 Element substance that cannot be broken any further by chem Rxn gt 92 naturally occurring symbols derived from German or Latin 0 Compound 2 elements combined in a fixed ratio ie table salt NaCl The Elements of Life 0 Essential Elements 2025 of the 92 naturally occurring gt Similar but humans need 25 plants 17 gt O C H N make up 96 of living matter gt Ca P K S and others 4 0 Trace Elements required in small doses ie Fe needed by all life gt Iodine I needed by vertebrate thyroid to produce certain horomones 5 mg adequate for humans Paucity goiter abnormal growth of thyroid Evolution of Tolerance and Toxic Elements some species adapted to environments with toxic elements ie serpentine by means of natural selection 22 Elemental Properties Depend on Atom Structure Atom smallest unit of matter that still has the properties of an element Subatomic Particles protons neutrons electrons 0 Atomic Nucleus protons and neutrons tightly packed center of atom surrounded by electron cloud 0 Neutron and proton have almost identical mass measured by a daltonamu Atomic and Mass 0 Atomic of protons 2He 2 0 Mass sum of protons and neutrons ie2311Na ll protons 12 neutrons 0 Atomic Mass total mass of an atom Isotopes more neutrons than usual 0 Radioactive Isotope nucleus decays spontaneously giving off particles and energy ie 14C gt When decay changes of proton forms different element Radioactive Tracers 0 Radioactive isotopes used as diagnostic tools incorporated into biologically active molecules gt Ex kidney tests PET scanners Radiometric Dating measure ratio of different isotopes and calculate half lives time for 50 to decay 0 Uranium238 has half life of 45bill The Energy Levels of Electrons 0 Energy capacity to cause change gt Potential energy energy due to location or structure gt Atoms have PE due to distance from nucleus also determined by energy lvl gt Electron shell house e electrons with different energies at certain distance from nucleus First shell has lowest PE Chapter 2 Page 1 When e absorbs energy it moves further from the nucleus Electron Distribution and Chem Properties 0 lst shell 2e 2nd 8e 0 Valence e outermost e Valence shell outermost e shell Electron Orbitals 0 Orbital 3D space where e is found no more than 2 per orbital gt e shell contains e at particular energy lvl in orbitals of distinct shape and orientation gt First shell has ll ls 2nd shell 2s 2p gt Reactivity is a result of unpaired e 23 Form and Fxn of a Molecule Depend on Bonds Atoms with incomplete shells combines with others to form octet 8 e Chemical bond sharingtransferring of valence e that result in atomic attractions Covalent Bonds sharing of a pair of valence e by 2 atoms 0 Molecule 2 or more atoms held together by covalent bonds 0 Representing a molecule gt Molecular Formula H2 2 atoms of H gt Lewis dot Structure symbols surrounded by dots that represent valence e gt Structural Formula H H line single bond shared pair of e OO double bond 0 Valence bonding capacity that of e required to reach octet 0 Electronegativity attraction of an atom for the e of a covalent bond gt More eneg stronger pull towards that atom gt nonpolar standoff polar no equal sharing Ionic Bonds some sharing is so unequal that one atom strips the valence e away from another 0 Ion resulting oppositely charged atoms of A gt Cation Anion bc of opposite charges they are attracted gt Any two ions of opposite charges can for an ionic bond gt ion Also applies to charged molecules 0 Salt ionic compound compounds formed by ionic bonds gt May be affected by environment Weak Chemical Bonds hold many large biological molecules held in place Hydrogen Bonds H covalently bonded to e neg atom Ex H2O 2H 0 NH3 N 3H Van der Waals 0 Changing regions of and charge that enable atoms and molecules to stick e not evenly distributed and accumulate in one place or another 0 Allow gecko to stick to surfaces Molecular ShapeFXN 0 Shape determined by position of atom39s orbitals 0 Shape determines how molecules recognize and respond 24 Chem Rxn Make and Break Bonds 0 Chem RXn making and breaking of bonds leading to changes in matter composition gt Reactants starting materials products ending gt All are reversible gt Rate affected by concentration more molecules more interactions gt Chemical Equilibrium point at which reactions balanced still ongoing but no net effect Chapter 2 Page 2
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