Transcript Chapter 2
Chapter 2 The Chemical Context of Life Basic Terms Element = cannot be broken down to other substances Examples: Na, O, C, Cl Compound = combination of 2 or more different elements Examples: NaCl, CO2, CH4 Requirements for Life 92 natural elements… 25 are essential to life Carbon, oxygen, hydrogen, and nitrogen make up 96% of living matter Trace elements are needed, too, though Iodine…lack of = goiter!! Atomic Structure Atom = smallest possible amount of an electron that retains the element’s properties Subatomic particles: Protons = + charge Electrons = - charge Neutrons = neutral charge Atomic Structure Atomic Number: # of protons (also equals # of electrons…) Mass Number: # of protons + # of neutrons Examples Isotopes Def’n: atoms that have more neutrons than atoms of the same element Same number of protons, but different number of neutrons Therefore…different atomic mass! Radioactive Isotopes Radioactive Isotopes: Nucleus decomposes spontaneously, giving off particles and energy (ie. Carbon 14) Uses: Dating fossils Tracers marking something and finding it again later Energy Energy = the ability to do work Energy levels Further out = more energy Electron Orbitals Electrons move within orbitals Orbitals are 3-D spaces, not linear Valence Shells Valence shell = outermost energy level Valence shell determines an atom’s reactiveness Alone = reactive/unhappy! Paired = nonreactive/happy ! Chemical Bonding 2 types of bonding that occurs between atoms: Covalent bonding Ionic bonding Covalent Bonds Def’n: 2 atoms share a pair of valence electrons Valence = bonding capacity Covalent Bonds Nonpolar covalent bonds Polar covalent bonds Electrons are shared equally between 2 atoms Electrons are NOT shared equally between 2 atoms Whether a bond is nonpolar and polar is determined by an atom’s electronegativity Electronegativity = how much an atom wants to pull its electrons to itself Ionic Bonds Def’n: one atoms “donates” its electrons to the other Cation = atom that donates, + Anion = atom that receives, - Hydrogen Bonds A hydrogen atom that is covalently bonded to one electronegative atom is also attracted to another electronegative atom Usually between oxygen of one water molecule and hydrogen of another Individually weak, but strong together! Molecular Shape & Function Molecules have characteristic sizes and shapes Molecular shape is crucial in biology because it determines how biological molecules recognize and respond to each other with specificity Examples: ?? Applications Morphine Lock and key concept Morphine is designed to be the same shape as endorphins Therefore, morphine will bind to the endorphin binding site in the brain Brain will be tricked! Heroin works in the same way Chemical Reactions Def’n: the making and breaking of chemical bonds Reactants Products 1st Law of Thermodynamics: Energy can be neither created nor destroyed