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Atoms - • Bond is union b/w electrons in outer shell of...

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Atoms, Molecules, and Life CH. 2 8-31-09 What are Atoms? Fig. 2-1 Basic structural unit of matter (i.e. smallest pieces of stuff) o Protons- Positive charge o Electrons- negative charge o Neutrons- no charge Elements differ in # of protons (fig. 2-2) Has specific physical and chemical properties Can’t be broken down by chemical rxn’s Atomic mass = # of protons and neutrons Building-Up Principle Electrons fill the shell closest to the nucleus, then occupy the next shell o 1 st shell- 2 electrons o 2 nd shell- 8 electrons o 3 rd shell- 8 electrons o Example: Atomic # of Carbon is 6, 2 in 1 st shell 4 in 2 nd shell Isotopes Atomic mass = # of protons and neutrons Isotopes vary in number of neutrons Ions Ions are atoms that vary in the # of electrons in outer shell Atoms are most stable when outer electron shell is full
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Extra electrons = negative charge Fewer electrons create a positive charge Chemical Bonds, Molecules, and Compounds
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Unformatted text preview: • Bond is union b/w electrons in outer shell of atoms • Atoms bond to form molecules • Molecules may contain atoms of only one element O2 • Molecules of compounds contain more thatn one element H2O Important Bonds in Biological Molecules • Ionic Bonds o Attraction between Ions Sodium has 1 electron in outer shell: chlorine has 7 Sodium can lose 1 and chlorine can gain it Sodium becomes a + ion Chlorine becomes a - ion • Covalent Bonds o Atoms share a pair or pairs of electrons to fill outermost shell Single covalent bond • Plus 1 pair electrons Double covalent bond • Plus 2 pairs Triple • plus 3 o Nonpolar if atoms share electrons equally Hydrogen gas (H-H) o Polar if electrons spend more time orbiting one atom and less around another Fig. 2-4 • Hydrogen Bonds...
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