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The Chemistry of Life

The Chemistry of Life. Why are we studying chemistry?. Chemistry is the foundation of Biology. Everything is made of matter Matter is made of atoms. Hydrogen 1 proton 1 electron. Oxygen 8 protons 8 neutrons 8 electrons. Proton. +. Neutron. 0. Electron. –. The World of Elements.

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The Chemistry of Life

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  1. The Chemistry of Life

  2. Why are we studying chemistry? Chemistry is the foundation of Biology

  3. Everything is made of matter • Matter is made of atoms Hydrogen 1 proton 1 electron Oxygen 8 protons 8 neutrons 8 electrons Proton + Neutron 0 Electron –

  4. The World of Elements H C N O Na Mg P S K Ca Different kinds of atoms = elements

  5. Life requires ~25 chemical elements • About 25 elements are essential for life • Four elements make up 96% of living matter: • carbon (C) • hydrogen (H) • oxygen (O) • nitrogen (N) • Four elements make up most of remaining 4%: •phosphorus (P)•calcium (Ca) •sulfur (S) •potassium (K)

  6. Bonding properties • Effect of electrons • electrons determine chemical behavior of atom • depends on numberof electrons in atom’s outermost shell • valence shell How does this atom behave?

  7. What’s themagic number? Bonding properties • Effect of electrons • chemical behavior of an atom depends on number of electrons in its valence shell How does this atom behave? How does this atom behave?

  8. Elements & their valence shells Elements in the same row have the same number of shells Moving from left to right, each element has a sequential addition of electrons (& protons)

  9. Elements & their valence shells Elements in the same column have the same valence & similar chemical properties Remember some food chainsare built on reducing O to H2O & some on reducing S to H2S

  10. – – – Chemical reactivity • Atoms tend to • complete a partially filled valence shell or • empty a partially filled valence shell This tendency drives chemical reactions… and creates bonds

  11. – – H2 (hydrogen gas) Hydrogen bond Bonds in Biology H2O • Weak bonds • hydrogen bonds • attraction between + and – • hydrophobic & hydrophilic interactions • interaction with H2O • van derWaals forces • (ionic) • Strong bonds • covalent bonds H2O Covalent bond

  12. H H O Oxygen H – H – Covalent bonds • Why are covalent bonds strong bonds? • two atoms share a pair of electrons • both atoms holding onto the electrons • very stable • Forms molecules H — H H2 (hydrogen gas) H2O (water)

  13. H – H–C–H – H Multiple covalent bonds • 2 atoms can share >1 pair of electrons • double bonds • 2 pairs of electrons • triple bonds • 3 pairs of electrons • Very strong bonds More isbetter!

  14. Nonpolar covalent bond • Pair of electrons shared equally by 2 atoms • example: hydrocarbons = CxHx • methane (CH4 ) balanced, stable,good building block

  15. H Oxygen H Polar covalent bonds • Pair of electrons shared unequally by 2 atoms • example: water = H2O • oxygen has stronger “attraction” for the electrons than hydrogen • oxygen has higher electronegativity • water isa polar molecule • + vs – poles • leads to many interesting properties of water… + – – – – +

  16. Hydrogen bonding • Polar water creates molecular attractions • attraction between positive H in one H2O molecule to negative O in another H2O • also can occur wherever an -OH exists in a larger molecule • Weak bond H H O Let’s go to the videotape!

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