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Lecture 3 BIO - Lecture 3 Chapter 2 Atoms Molecules The...

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8 Lecture 3: C h apter 2 – A toms & Mo l ecu l e s : The C hem i cal B a s i s of L i fe I. El e m e n t s & A t o m s are substance that cannot be broken down into simpler substances by ordinary chemical reactions A . I m por t ant El e m e n t s Carbon, Hydrogen, Oxygen, & Nitrogen are the most abundant elements in living things (about 96% of mass) 1. Carbon backbone of organic molecules 2. H ydrogen component of water 3. N it rogen component of proteins, nucleic acids, & chlorophyll 4. O xygen required for cellular respiration component of water B. A t om 1. N uc l eus contains protons (+) & neutrons (uncharged) 2. El ec t rons ( ) surround nucleus Each atom is a particular element identified by the number of protons (atomic number) Atomic Numbe r: fixed number of protons in the atomic nucleus Periodic Table : chart of elements arranged in order by atomic number Electron configuration : (Bohr Model) shows the electrons arranged in a series of concentric circles around the nucleus (2-8-8) C. A t o mi c M a s s sum of protons & neutrons D. A t o mi c M a s s U n i t (Dalton) Mass of a single proton or neutron Mass of an electron about 1/1800 of an A.M.U. Atomic mass typically written as a superscript & atomic number written as subscript; ex. 16 O E. I s o t ope – alternate form of an element with the same number of protons & electrons, but a different number of neutrons and therefore a different mass -radioisotopes emit radiation when they decay…autoradiography – in which raditation causes the appearance of dark silver grains in the photographic film. Unstable isotope goes through process of decay to stable isotope, by emitting radiation ( ϐ particles) F. O rb it a l s Electrons move rapidly in electron orbitals outside the nucleus 1. El ec t ron s he l l
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23 – electrons in orbitals with similar energies, said to be at the same principal energy level 2. V a l ence e l ec t rons most energetic electrons, which occupy the valence shell
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