The Chemical Context of Chapter 2 The Chemical Context of Life

Matter Anything that has mass and volume. Made up of elements An element is a substance that can not be broken down to other substances by chemical reactions. 92 elements occur in nature Two or more different elements bond together in a fixed ratio to form compounds which have different characteristics from the elements involved.

Essential Elements of Life Carbon Oxygen Hydrogen Nitrogen Calcium, Phosphorus, Potassium, Sodium, Chlorine, and Magnesium make up the remaining 4% of an organisms weight. Trace Elements Required by organisms in minute quantities Make up less than 0.01% of an organisms weight. Boron, Chromium, Cobalt, Copper, Fluorine, Iodine, Iron, Manganese, Molybdenum, Selenium, Silicon, Tin, Vanadium, and Zinc. Make up 96% of living matter.

Atom Structure Atom is the smallest unit of matter that still retains the properties of an element. Subatomic particles Neutrons Found in nucleus Neutral charge Mass about 1dalton or amu (atomic mass unit) Proton Positive charge Atomic number Mass number

Electrons Located outside nucleus Negative charge Mass equal to one two-thousandth of a proton or neutron. Kept close to nucleus due to opposite attraction to positively charged protons.

Transmutation Group Activity Isotopes Atoms of a given element with the same number of protons, but a different number of neutrons. Carbon 12 and Carbon 13 are stable isotopes, meaning that their nuclei do not have a tendency to lose particles. Carbon 14 is unstable or radioactive. Nuclear decay is spontaneous, giving off particles and energy. If proton number changes then, it transforms the atom to an atom of a different element. Transmutation Group Activity

Radioactive Isotopes Useful: Radioactive tracers to monitor biological processes in plants & animals. Archeological dating Medical uses Smoke detectors Food irradiation To solve crimes Pest control Energy source For more information check out The Berkeley Laboratory Isotopes Project's http://ie.lbl.gov/education/isotopes.htm Dangerous exposure of radiation from decaying isotopes can pose a hazard to life by damaging cellular molecules

Energy Levels of Electrons An atom’s electrons vary in the amount of energy they possess Energy level is correlated with its average distance from the nucleus Represented by electron shells (average distance of electrons from nucleus) 1st energy level, closest to nucleus has the lowest potential energy Electrons can move from one level to another only if the energy it gains or loses is exactly equal to the difference in energy between the two levels.

Optional Activity: Design a computer animated model of your favorite atom. Build an Atom Tutorial http://www.webwasp.co.uk/tutorials/b09-atom/tutorial.php

Chemical Properties Chemical behavior of an atom is determined by its electron configuration or the distributions of electrons in the atom’s electron shells especially the valence electrons. 1st electron shell holds a maximum of 2 electrons 2nd electron shell holds a maximum of 8 electrons 3rd electron shell holds a maximum of 18 electrons 4th electron shell holds a maximum of 32 electrons

Electron Orbitals Three-dimensional space where an electron is found 90% of the time. Orbitals S P D F No more than two electrons can occupy a single orbit. Therefore, p, d, and f orbitals are Actually made of a -x, -y, and -z planes or sublevels.

Electron Configurations The electron configuration of an atom is a form of notation which shows how the electrons are distributed among the various atomic orbital and energy levels.  The format consists of a series of numbers, letters and superscripts as shown below: 1s2 Log onto: Science Help On-line Chemistry for a quick tutorial in Electron Configurations http://www.fordhamprep.org/gcurran/sho/sho/lessons/lesson36.htm

Chemical Bonding Formation and function of molecules depend on chemical bonding between atoms. Atoms with incomplete valence shells can interact with certain other atoms in such a way that each partner completes its valence shell. Share valence electrons Transfer valence electrons

Covalent Bond Sharing of a pair of valence electrons by two atoms. An attraction of a particular kind of atom for the electrons of a covalent bond is called its electronegativity. The more electronegative an atom, the more strongly it pulls shared electrons toward itself Nonpolar covalent bond Bonds between two atoms with same electronegativity Polar covalent bond One atom is bonded to a more electronegative atom Strong chemical bond.

Ionic Bonds Unequal attraction of valence electrons More electronegative atom strips an electron completely away from its partner Anion Negatively charged ion Gained one or more electrons Cation Positively charged ion Lost one or more electrons Both atoms end up with their valence shells complete. Compounds formed by ionic bonds are called ionic compounds or salts. Environment affects the strength of ionic bonds. Ionic bond considered to be a weak bond. Attracted to each other. Attraction is called an Ionic bond.

Weak bonds Hydrogen Bonds Van der Waals Interactions Forms when a hydrogen atom covalently bonded to one electronegative atom is also attracted to another electronegative atom. Usually partners with oxygen or nitrogen in living cells. Van der Waals Interactions Occur only when atoms and molecules are very close together Constant motion of electrons can cause them to accumulate in one part of the molecule at any given time causing a “hot spot” of positive and negative charge allowing atoms and molecules to stick to one another. * Note: Although these bonds are individually weak, their cumulative effect is very strong. (Protein, Gecko lizard)

Compounds Formed when two or more elements of compounds bond together. Based on valence number C +4 + Cl -1 = CCl4 Type of bond formed based on electronegativity CCl4 will have polar covalent bonds When mixed in solution it is important to remember: 1 mole = grams = mass number Molecules = 6.02 x 1023 for a 1 liter solution

Molecular Shape and Function A molecules size and shape is very important to its function in the living cell. Determines how biological molecules recognize and respond to one another. Only molecules with complementary shapes are able to bind to each other by weak bonds. Molecular shape is determined by the position of the atoms’ orbitals. Endorphins bind to receptors on the surface of brain cells to relieve pain.

Chemical Reactions Change reactants into products while conserving matter. Most are reversible. Chemical equilibrium does not mean the reactants and products are equal in concentration, but only that their concentrations have stabilized at a particular ratio. “Dynamic Equilibrium”

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