8/25/20111Living organisms are composed of about 25 chemical elementsMost Common ElementsIn the Human Body (96%)Essential Trace ElementsIn the Human Body (0.01%)Trace elements are common additives to food and water8/25/20112Elements can combine to form compoundsAtoms consist of protons, neutrons, and electronsIsotopes• Carbon-12: Protons-6 Neutrons-6 Electrons-6• Carbon-13: Protons-6 Neutrons-7 Electrons-6• Carbon-14: Protons-6 Neutrons-8 Electrons-6Carbon Will Always Have 6 ProtonsOnly The Number Of Neutrons Change in Isotopes!8/25/20113Radioactive isotopes can help or harm usElectron arrangement determines the chemical properties of an atomIonic bonds are attractions between ions of opposite charge8/25/20114Covalent bonds join atoms into molecules through electron sharingUnequal electron sharing creates polar moleculesHydrogen bonds are weak bonds important in the chemistry of lifePartial Positive EndPartial Negative End8/25/20115Hydrogen bonds make liquid water cohesiveWaters hydrogen bonds moderate temperature Ice is less dense than liquid water8/25/20116Water is the solvent of lifeThe chemistry of life is sensitive to acidic and basic solutionsAcidic Solutions have A High Concentration of H+ IonsNeutral Solutions have equal concentrations of H+ and OH-IonsBasic Solutions have a low concentration on H+ IonsThe search for extraterrestrial life centers on the search for water8/25/20117Chemical reactions make and break bonds, changing the composition of
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