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The Chemistry of Life Chapter 2

The Chemistry of Life Chapter 2. Why are we studying chemistry?. Chemistry is the foundation of Biology. Everything is made of matter. Matter is made of atoms, it is anything that occupies space. Hydrogen 1 proton 1 electron. Oxygen 8 protons 8 neutrons 8 electrons. Proton. +.

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The Chemistry of Life Chapter 2

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  1. The Chemistry of LifeChapter 2

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

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

  4. Matter • Matter is found on the Earth in three physical states • Solid • Liquid • Gas

  5. Atoms • Each element consists of one kind of atom • An atom is the smallest unit of matter that still retains the properties of an element Nucleus (a) (b) Cloud of negative charge (2 electrons) 2 Protons Neutrons 2 Electrons 2 Figure 2.5

  6. The Structure of Atoms • Atoms are composed of subatomic particles • A proton is positively charged • An electron is negatively charged and found in orbitals – three-dimensional region around the nucleus. • A neutron is electrically neutral

  7. The World of Elements– substances that cannot be broken down chemically into smaller kinds of matter. H C N O Na Mg P S K Ca Different kinds of atoms = elements

  8. Atomic Number and Atomic Mass • Atomic Number is equal to the number of protons • The number of protons also equal the number of electrons in a neutral atom. • Atom Mass is equal to the number of protons + neutrons.

  9. Isotopes • They have the same number of protons and electrons • But they have a different number of neutrons

  10. Electron Arrangement and the Chemical Properties of Atoms • Electrons determine how an atom behaves when it encounters other atoms • Electrons orbit the nucleus of an atom in specific electron shells • The number of electrons in the outermost shell determines the chemical properties of an atom

  11. 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)

  12. Atoms of the four elements most abundant in life First electron shell (can hold 2 electrons) Outermost electron shell (can hold 8 electrons) Electron Hydrogen (H) Atomic number = 1 Carbon (C) Atomic number = 6 Nitrogen (N) Atomic number = 7 Oxygen (O) Atomic number = 8 Figure 2.7

  13. Compounds • Made of atoms of two or more elements in fixed proportions. Chemical Bonds • Attractive forces that hold together atoms. Molecule • Simplest part of a substance that retains all of the properties of the substance and can exist in a free state.

  14. 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?

  15. 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?

  16. 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)

  17. Elements & their valence shells Elements in the same column have the same valence & similar chemical properties

  18. – – – 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

  19. – – 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 bonds) • Van der Waals forces' are the attraction of intermolecular forces between molecules • Strong bonds • covalent bonds H2O Covalent bond

  20. Hydrogen Bonds Water molecules carry slight charges Electrons favor O over H Hydrogen bonds form between O of one and H of another + – O H + H – O H + HydrogenBonds + H +

  21. Ionic Bonds • When an atom loses or gains electrons, it becomes electrically charged Sodium atom (Na) Chlorine atom (Cl) • Charged atoms are called ions • Ionic bonds are formed between oppositely charged ions Complete outer shells Sodium ion (Na) Chloride ion (Cl) Sodium chloride (NaCl) Figure 2.8

  22. Covalent Bonds • A covalent bond forms when two atoms share one or more pairs of outer-shell electrons

  23. 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)

  24. 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!

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

  26. 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… + – – – – +

  27. 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

  28. Energy and Matter The motion and spacing between atoms of a substance determine the substance’s state. States of matter

  29. States of Matter • Solid – maintains a fixed volume and shape. • Molecules are linked closely • Particles of solids move less rapidly • Liquid – maintains a fixed volume. • Particles move more freely than those of a solid, gives liquid the ability to flow. • Gas – particles have little or no attraction to each other and fill the volume of the container they occupy. • Particles move most rapidly. Thermal energy must be added to the substance to cause a substance to change states.

  30. Energy and Chemical Reactions • One or more substances change to produce one or more different substances. • Energy is absorbed or released when chemical bonds are broken and new ones are formed. • Metabolism – term used to describe all the chemical reactions that occur in an organism.

  31. Chemical Reactions • Cells constantly rearrange molecules by breaking existing chemical bonds and forming new ones • Such changes in the chemical composition of matter are called chemical reactions Hydrogen gas Oxygen gas Water Products Reactants Unnumbered Figure 2.1

  32. Reactants and Products • Reactants are substances that enter chemical reactions. • Products are substances produced by chemical reactions

  33. Chapter 2 Energy and Chemical Reactions

  34. Activation Energy • This is the energy that must be added to the reaction for it to begin. So this is the amount of energy needed to start the reaction. • Activation Energy • Enzymes - are proteins that lower the amount of activation energy necessary for a reaction to begin in living systems. • They speed up metabolic reactions without being permanently changed • Enzymes are catalysts – they are chemical substances that reduce the activation energy needed for a reaction to take place.

  35. Oxidation / Reduction • Oxidation Reduction Reactions • A chemical reaction in which electrons are exchanged between atoms is called an oxidation-reduction reaction. • Oxidation reactions – a reactant looses one or more electrons, thus becoming more positive in charge. So in forming sodium chloride (salt), sodium looses an electron becoming more positive and is thus oxidized. It becomes the sodium ion. Na+ ion.

  36. Oxidation / Reduction (continued) • Reduction Reaction – a reactant gains one or more electrons thus becoming more negative in charge. When chlorine atom gains an electron to form the CL- ion, the atom undergoes reduction. • Redox Reactions always occur together.

  37. Chemistry of Life Properties of Water

  38. More about Water Why are we studying water? All life occurs in water • inside & outside the cell

  39. WATER AND LIFE • Life on Earth began in water and evolved there for 3 billion years • Modern life still remains tied to water • Your cells are composed of 70%–95% water

  40. The Structure of Water • Studied in isolation, the water molecule is deceptively simple • Its two hydrogen atoms are joined to one oxygen atom by single covalent bonds H H O Unnumbered Figure 2.2

  41. But the electrons of the covalent bonds are not shared equally between oxygen and hydrogen • This unequal sharing makes water a polar molecule () () () () Figure 2.11a

  42. Chemistry of water • H2O molecules form H-bonds with each other • +H attracted to –O • creates a sticky molecule

  43. The polarity of water results in weak electrical attractions between neighboring water molecules () Hydrogen bond () () () • These interactions are called hydrogen bonds () () () () (b) Figure 2.11b

  44. Water’s Life-Supporting Properties • The polarity of water molecules and the hydrogen bonding that results explain most of water’s life-supporting properties • Water’s cohesive nature • Water’s ability to moderate temperature • Versatility of water as a solvent

  45. Properties of Water 1. cohesion & adhesion • surface tension, capillary action 2. good solvent • many molecules dissolve in H2O • hydrophilic vs. hydrophobic 3. lower density as a solid • ice floats! 4. high specific heat • water stores heat 5. high heat of vaporization • heats & cools slowly Ice!I could use more ice!

  46. 1. Cohesion & Adhesion • Cohesion • H bonding between H2O molecules • water is “sticky” • surface tension • drinking straw • Adhesion • H bonding between H2O & other substances • capillary action • meniscus • water climbs uppaper towel or cloth Try that with flour…or sugar…

  47. The Cohesion of Water • Water molecules stick together as a result of hydrogen bonding Microscopic tubes • This is called cohesion • Cohesion is vital for water transport in plants Figure 2.12

  48. How does H2O get to top of trees? Transpiration is built on cohesion & adhesion

  49. Cohesionamong Water Molecules

  50. Surface tension is the measure of how difficult it is to stretch or break the surface of a liquid • Hydrogen bonds give water an unusually high surface tension Figure 2.13

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