11 216 covalent bonds types of chemical bonds covalent

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Unformatted text preview: Beta-carotene Vitamin A (2 molecules) Tables 2.11 & 2.16 Covalent Bonds Types of Chemical Bonds • Covalent Bonds • Ionic Bonds • Hydrogen Bonds • Atoms share electrons to fill valence shell • Electrons are shared in pairs • Each pair forms one bond Example: Water (H2O) Two atoms can share more than one pair of electrons • Oxygen: 6 valence e– – Needs 2 e – to fill shell – Gets 1 e – from each hydrogen atom • Double bonds: H O=O C=C H • Triple bonds: N≡N • Hydrogen: 1 valence e– – Each needs 1 e – to fill shell – Each gets 1 e – from oxygen H C C H Covalent bonds Heyer 3 Biological Chemistry Ionic Bonds • Based on electromagnetic attraction between ions of opposite charge • Ions: charged atoms – Loss of e–: positive charge on atom – Gain of e–: negative charge on atom Ionic bond between Na+ and Cl– form NaCl, table salt • Regular stacking of atoms cause salts to form crystals in absence of water • Salts: two ions of opposite charge bonded together Ions separate in presence of water • Dissociation: breaking of ionic bond • Dissolve: surrounding a molecule like NaCl with H2O • Why? Because water is a polar molecule. Water is a polar molecule • Nucleus of oxygen bigger than hydrogen • Bigger nucleus attracts e– better • Distribution of electrons is uneven around molecule Water is a versatile solvent Dissociated ions in water Negative Oxygen regions of polar water molecules are attracted to sodium cations (Na+). Na + – + – Positive hydrogen regions of water molecules cling to chloride anions (Cl–). Cl – – Na + + Cl – – + – + + + – + – + – – – Salt ions dissolving in water Na+ surrounded by Cl– surrounded by oxygen side of H2O hydrogen side of H2O Heyer Glucose dissolved in water • Solutes whose charges or polarity allow them to stick to water molecules dissolve in water – they form aqueous solutions 4 Biological Chemistry Aqueous Solutions Polar or ionic molecule dissolved in water forms a solution • Solution: solutes dissolved by a solvent • Solvent = water • Solutes = dissolved substance Water: the “universal solvent” • Many substances dissolve in water • Examples of water soluble substances: – Salts (ions, or electrolytes) – Sugars and other nutrients – Vitamins – Hormones A protein solution = protein dissolved in water Hydrogen bonds form between partial (∂) charges • Both intermolecular and intramolecular ß H of am...
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