BIOL 240 1st Edition Lecture 1Current LectureChapter 2: The Chemical Context of LifeI. Matter: takes up spacea. Elements (92 in nature)i. Essential elements: carbon, hydrogen, oxygen, nitrogen, phosphorous, and sulfurii. Trace elements: help with enzymesb. Compoundsi. More than one element bound togetherc. Atom: smallest unit with the properties of an elementi. Nucleus: houses protons and neutrons1. Protons: positive charge; determines element2. Neutrons: neutral charge; determines isotopeii. Around the nucleus: houses electrons1. Electrons: negative charge; determines overall charge and chemical behavioriii. Atomic number = number of protonsiv. Mass number = number of protons + number of neutronsv. Isotope: same number of proton as original element, different number of neutrons, same atomic number, different mass number1. Important because of: radioactivity (x-ray) and carbon dating (carbon-14)d. Energy levels of electronsi. The further away the electrons are from the nucleus, the greater the energy of the electrons1. When an electron drops from a higher shell to a lower shell, energy is lost2. When an electron jumps from a lower shell to a higher shell, energy is absorbedii. Chemical behavior of an atom depends on:1. Its valence shell: the outermost shell that contains electrons2. Its valence electrons: the electrons on the outermost shelliii. The Periodic Table follows a trend determined by the elements’ chemical behavior:1. 1st Row: elements with one valence shellThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.2. 2nd Row: elements with two valence shells3. 3rd Row: elements with three valence shells, etc.II. Chemical bondsa. Ionic: atoms combine to form molecules and ionic compoundsi. Valence shells go from incomplete to complete valence shellsb. Covalent: two atoms share a pair of valence electronsc. Compound vs. Moleculesi. Compound: different elements combinedii. Molecules: same element combinedd. Single bond vs. Double bondi. Single bond: only one pair of electrons are sharedii. Double bond: two pairs of electrons are sharede. Bond is formed when valence shell is fullf. Electronegativity: determines molecular shapei. Covalent1. Attraction of a particular atom for the electrons of a covalent bond2. Nonpolar covalent bond: equal pulling3. Polar covalent bond: unequal pullingii. Ionic1. So unequal in valence shell attraction that the electron is stripped away2. Bond is formed due to opposite chargeg. Weak chemical bondi. Advantage: Does not stay together very well if you want it to break apart, used in constant changing molecules/ compoundsii. Hydrogen