BIOL 1140 1st Edition Lecture 2 Outline of Last Lecture I. Characteristics of LifeOutline of Current Lecture II. Structure of Elements Continueda. Atomic Mass b. Isotopesc. Ionsd. Electron Shellse. Covalent Bondsf. Ionic BondsCurrent LectureI. Elements a. The same element can different atomic massi. Mass = protons + neutronsii. Different atomic mass versions called isotopes1. Example: Carbon. Atomic number 6. a. Must have 6 Protons and 6 Electrons to make carbons chemically neutral 2. Example: Nitrogen Atomic Number 7a. Always has 7 protons, must have 7 electrons to be neutral b. If carbon had 6 neutrons, atomic mass is 12 (P+N=AM)c. If carbon had 8 neutrons, atomic mass if 14d. Protons always the same, neutrons can vary by isotopeb. Isotopesi. Forms of an element with a different number of neutrons than the usual number1. Always have same atomic number (number of protons)2. Different atomic mass (Protons plus neutrons)ii. Radioisotopes - unstable isotopes1. Give off radiation energya. Can be harmful, useful (medicine- MRI, CAT Scan), used to determine age of fossilc. Ionsi. Form of an atom with different number of electrons 1. Atom can gain or lose electrons in chemical reactionsThese 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. Example: Na has 11 protons, 11 electrons. If lost an electron, (11p,10e), it is unbalanceda. Positively charged Ion. Written NA+ d. Electronsi. Arranged in Shells1. Reaction can be predicted based on number and arrangement of electrons in atom 2. Each shell can only hold a certain number of electrons ii. 1st Shell (inner most shell) holds up to 2 electronsiii. 2nd Shell holds up to 8iv. 3rd shell holds up to 8 1. If an atom only has 1-2 electrons, only 1st shell is used 2. If an atom has 6 electrons, then 2 will go in 1st shell, remaining 4 will go in 2nd shellv. We will never work with atoms above 18 electrons.vi. Atoms are most stable when outermost shell is full 1. Inert Atoms (He, Ne, Ar) already have full outer shells and are unreactivevii. Atoms will interact with other atoms to fill their outermost shells 1. Chemical Bonds- attractive forces holding atoms together e. Covalent Bondsi. Shared electrons1. CH4 - Methanea. Carbon has 6 electronsi. 2 in 1st shellii. 4 in 2nd shellb. Hydrogen has 1 electron. c. Carbon + 4 Hydrogen = full outer shell of 8 electrons (plus 2 inner electrons) ii. Drawn as H-Hiii. Electronegative1. "electron hog", don’t share electrons well2. Oxygen, Nitrogen are examples iv. Nonpolar Covalent Bonds1. Electrons are shared equallyv. Polar Covalent Bonds1. Electrons NOT shared equallya. One atom has stronger pull on the electrons f. Ionic Bondsi. Ion - An electronically charge atom or Molecule1. Positively charged ion: forms when electron is lost2. Negatively charged ion forms when electron is
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