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, CO 2, CH 4

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 Electrons are shared equally between 2 atoms  Polar covalent bonds 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  1 st Law of Thermodynamics: Energy can be neither created nor destroyed