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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
The Chemical Basis of Life
  • Elements, Atoms and Molecules
  • Water’s Life-Supporting Properties
  • Chemical Reactions
living organisms are made of elements
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
chemicals of life
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
elemental deficiencies
Elemental Deficiencies
  • Iron (Fe): anemia
    • Added to cereal
  • Iodine (I): goiter
    • Added to salt
  • New avenue: genetically improved foods (GM crops): Vitamin A
elements form compounds
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
  • 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

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

elemental differences
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
radioactive isotopes
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)
electrons affect chemical properties
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
covalent bonds
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)
ionic bonds
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)
hydrogen bonds
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
chemical reactions
Chemical Reactions
  • Reactants ‘before’ arrow, products ‘after’
  • Must be balanced
water s properties
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
more water properties
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?
  • Compound that accepts H ions: base
    • Example: NaOH (sodium hydroxide)
  • Compound that donates H ions: acid
    • Example: HCl (hydrochloric acid)
  • Scale from 0 - 14
acid precipitation
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