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The Chemical Basis of Life

The Chemical Basis of Life. Elements, Atoms and Molecules Water’s Life-Supporting Properties Chemical Reactions. Living Organisms are Made of Elements. Living organisms composed of matter Matter: anything that occupies space and has mass

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The Chemical Basis of Life

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  1. The Chemical Basis of Life • Elements, Atoms and Molecules • Water’s Life-Supporting Properties • Chemical Reactions

  2. Living Organisms are Made of Elements • Living organisms composed of matter • Matter: anything that occupies space and has mass • Element: substance that cannot be broken down to other substances by ordinary chemical means • Chemists recognize 92 natural elements • Life requires 25 of these

  3. Chemicals of Life • Four make up about 96% of the human body • Ca, P, K, S, Na, Cl, Mg make up most of the rest • Trace: B, Cr, Co, Cu, F, I, Fe, Mn, Mo, Se, Si, Sn, V, Zn

  4. Elemental Deficiencies • Iron (Fe): anemia • Added to cereal • Iodine (I): goiter • Added to salt • New avenue: genetically improved foods (GM crops): Vitamin A

  5. Elements form Compounds • Compounds are composed of elements • Some have 2 elements, some have more • Compounds have novel properties • Some compounds have the same elements in the same proportions, but act differently

  6. Atoms • Smallest unit of matter that retains the properties of the element • Split into 3 particles: • Protons (+ charge) • Neutron (0 charge) • Electrons (- charge) • Nucleus: protons and neutrons • Electrons orbit the nucleus

  7. If the atom is the size of Yankee stadium, the nucleus is a fly in the center of the field and the electrons are the size of gnats buzzing around outside the stadium

  8. Elemental Differences • The number of protons defines an element: atomic number • Mass number: sum of protons and neutrons • Atomic mass: also includes electrons (very light) • Isotopes: differing numbers of neutrons- behave chemically identically to each other

  9. Radioactive Isotopes • Basic Research • Used to trace elements in organisms to see where they are active, where they go, etc. • We can literally see what happens to each atom in a compound as it is utilized • Medical Diagnosis • Can be used to find centers of chemical activity (cancer tissues have more activity) • Dangers • Damage to DNA (some man created some natural)

  10. Electrons Affect Chemical Properties • Electron orbits are called shells: • The inner-most: 2 e- • The outer shell for most elements: up to 8 e- • # in the outermost shell determines the reactivity of the element • Magic number: 8

  11. Covalent Bonds • Strong chemical bond • Two atoms share one or more pairs of outer shell electrons • Forms molecules (two or more atoms physically held together) • Two types: • Polar (unequal charges) • Non-polar (equal charges)

  12. Ionic Bonds • Tends to occur between elements with many/few electrons in outer shell • Element with many electrons takes one/some from element with few electrons • Forms ions (positive or negative charge)

  13. Hydrogen Bonds • H atoms involved in polar covalent bonds carry a slight positive charge • They can be attracted to atoms with slight negative charges (N, O are common) • H-bonds help define the properties of water, hold proteins together, hold DNA together, etc. • Biologically very important

  14. Chemical Reactions • Reactants ‘before’ arrow, products ‘after’ • Must be balanced

  15. Water’s Properties • Cohesion: H-bonds hold water molecules to each other • Trees, water-walkers • H-bonds help moderate temperature • Coastal areas have milder temps than inland areas (think SD compared to IE) • Evaporative cooling: when water evaporates, the molecules left behind have lower energy (cooler) • Used to cool greenhouses, people

  16. More Water Properties • Ice is less dense than water (UNUSUAL) • Each molecule forms H-bonds with 4 neighbors • Molecules end up maximally spaced • Ice floats! • Water is the solvent of life • Solution: liquid consisting of a uniform mixture of two or more substances • Solvent: dissolving agent • Solute: substance that is dissolved • Polar molecules dissolve readily in water. Why?

  17. pH • Compound that accepts H ions: base • Example: NaOH (sodium hydroxide) • Compound that donates H ions: acid • Example: HCl (hydrochloric acid) • Scale from 0 - 14

  18. Acid Precipitation • pH lower than 5.2 • Mostly caused by presence of sulfur and nitrogen oxides • Rain with pH 2 recorded on east coast, fog with pH 1.7 recorded in LA (probably Riv.) • Results from burning fossil fuels • How many drive SUVs? • Damaging forests, nutrient cycling, cities, ocean more acidic

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