Chapter 2 Chemical Context of Life Wakefield 2014

EVERYTHING IS MADE UP OF MATTER ANYTHING THAT TAKES UP SPACE & HAS MASS MADE UP OF PURE SUBSTANCES CALLED ELEMENTS ELEMENTS COMBINE TO FORM COMPOUNDS; MANY HAVING EMERGENT PROPERTIES Example: NaCl EVERYTHING IS MADE UP OF MATTER

M A T T E R

M A T T E R ABOUT 92 NATURALLY OCCURRING ELEMENTS 25 OF THESE ARE CONSIDERED ESSENTIAL TO LIFE 4 OF THESE MAKE UP 96% OF LIVING MATTER CARBON – C HYDROGEN – H OXYGEN – O NITROGEN – N REMAINING 4% OF LIVING MATTER IS COMPOSED OF P, S, Ca, & K TRACE ELEMENTS – REQUIRED IN MINUTE AMTS Fe, I, Mg etc.

Sub-Atomic Particles Neu = Neutral Pro = Positive Elec = Negative Nucleus = Center

Atomic Number & Mass Atomic # = # of Protons in the nucleus of the atom – never changes for each individual element Atomic Mass = Total of protons and the average # of neutrons of all Isotopes in the nucleus of an atom Isotope = Varying forms of an element due to varying #’s of neutrons

Isotopes

Isotopes All atoms of an element have the same # of protons Some atoms of an element have varying #’s of neutrons – isotopes of that element The more neutrons an isotope has the less stable it is Radioactive isotopes occurs when the nucleus of the atom decays spontaneously, giving off particles and energy – This decay leads to a change in the # of protons which eventually transforms it into another element due to the change in protons.

Radioactive Isotopes Many Useful Applicaitons: Date fossils Tracers Metabolism Production of DNA Cancer detection Kidney disorders Imaging PET Scans Hazardous – Radiation Poisoning Using Radioactivity

Energy Levels of Electrons Energy is the potential to do work Potential Energy – energy that matter and electrons possess because of its location or structure The different amounts of potential energy of an atom depends on the structure of the atom / the # and locations of its electrons Electrons are located in electron shells (electron levels or orbits) Each shell has a specific # of electron capacity See Page 36 of Text

Energy Levels of Electrons

Electron Configuration

Electron Configuration Chemical behavior depends mostly on the # of electrons in the atom’s outermost shell Valance Electrons - located in the outermost shell or valence shell If the atom’s valence shell is full it is unreactive otherwise it will readily react with other atoms Examples are the inert gases – He, Ne, Ar, etc.

Chemical Bonding Chemical Bond – achieved when atoms with incomplete valence shells interact with other such atoms Covalent Bond – occurs when the atoms share electrons in their valence shells – creates a molecule Ionic Bond – occurs when the atoms transfer valence electrons – form ionic compounds or salts

Chemical Bonding Molecule – formed when 2 or more atoms bond together by a covalent bond and has its own specific molecular formula (H2O) Compound – formed when the 2 atoms of a molecule are of different elements Single bond – 1 pair of shared valence electrons Double bond – 2 pairs of shared valence electrons Valence – bonding capacity of an atom

Chemical Bonding Electronegativity – attraction of a particular kind of atom for the electrons of a covalent bond

Covalent Bonding Nonpolar Covalent Bond – all electrons are shared equally

Covalent Bonding Nonpolar Covalent Bond Van der Waal Interaction - Example of weak nonpolar covalent bond So weak they only occur when atoms and molecules are VERY close together Biomimicary

Covalent Bonding Polar Covalent Bond – occurs when one atom is bonded a more electronegative atom; hence the electrons, though shared, are not shared equally

Ionic Bonding Occurs when electrons within the molecule are NOT shared but transferred – may create an ion – (+) or (-) charged particle Ions are critical in the energy transfer of cellular respiration Product - ionic compounds or salts Often found in nature as crystals The ratio of the molecular formula never changes but the shape of the crystal may

Ionic Bonding Occurs when electrons within the molecule are NOT shared but transferred – may create an ion – (+) or (-) charged particle Ions are critical in the energy transfer of cellular respiration Product - ionic compounds or salts Often found in nature as crystals The ratio of the molecular formula never changes but the shape of the crystal may

Molecular Shape & Function Each molecule has a unique shape and size Its precise shape is critical to its function Shape determines how biological molecules recognize and respond to one another

Chemical Reactions Always has a specific formula Make and break chemical bonds Energy is always involved – either used or released Reactants – starting materials Products – resulting materials Activation Energy – energy needed to initiate reaction

Chemical Reactions Chemical Equilibrium – occurs when reactions offset one another completely