Chapter 2.txt

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Chapter 2.txt
2011-01-02 23:07:33
AP Biology

Chapter 2
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  1. Acid, acidic
    [L. acidus, sour] Any water-soluble substance that releases hydrogen ions (H+) in water, yielding a pH below 7.0.
  2. Atom
    The smallest unit of an element that still retains the element�s properties.
  3. atomic number
    The number of protons in the nucleus of atoms of a given element.
  4. Base, basic
    Any water-soluble substance that releases hydroxyl ions in water to yield a pH greater than 7.0. Also the nitrogencontaining component of a nucleotide.
  5. Buffer system
    A weak acid and the salt that forms when it dissolves. The two work as a pair to counter slight shifts in pH.
  6. Chemical bonds
    A union between the electron structures of two or more atoms.
  7. cohesion
    A capacity to resist rupturing when placed under tension (stretched).
  8. Compound
    Molecule consisting of two or more elements in proportions that do not vary, as they can in mixtures.
  9. Covalent bond
    [L. con, together, + valere, to be strong] A sharing of one or more electrons between two atoms. In a polar covalent bond, the atoms share electrons unequally; in a nonpolar covalent bond, each atom gets an equal share of the electrons.
  10. Electron
    Negatively charged subatomicparticle. Electrons occupy orbitals around the atomic nucleus.
  11. Element
    Fundamental form of matter that cannot be degraded to a simpler form by ordinary means. All atoms of an element have the same atomic number.
  12. Evaporation
    Process of conversion of a liquid to a gas; requires energy input.
  13. Hydrogen bond
    A weak attraction that has formed between a covalently bonded hydrogen atom and an electronegative atom taking part in another covalent bond.
  14. Hydrogen ion, H+
    Free (or unbound) proton; one hydrogen atom that lost its electron and now bears a positive charge (H+).
  15. Hydrophilic
    [Gk. philos, loving] A polar molecule that dissolves easily in water; e.g., glucose.
  16. Hydrophobic
    [Gk. phobos, dreading] A nonpolar molecule that resists dissolving in water; e.g., oil.
  17. Ion
    Atom having an unequal number ofprotons and electrons; it carries a positive or negative electric charge.
  18. Ionic bond
    Ions interacting through the attraction of their opposite charges.
  19. Isotopes
    One of two or more atoms of the same element (same number of protons) that differ in their number of neutrons.
  20. Mass number
    Sum of protons and neutrons in the nucleus of an element�s atoms.
  21. Mixture
    Two or more types of molecules intermingled in proportions that can and usually do vary.
  22. Molecule
    Two or more covalently bonded atoms of the same or different elements.
  23. Neutron
    Type of subatomic particle in the nucleus of all atoms except hydrogen; has mass but no charge.
  24. Periodic table
    Tabular arrangement of elements in order of their increasing atomic number.
  25. PH scale
    Measure of the H+ concentration of a solution. pH 7 is neutral.
  26. Proton
    Positively charged subatomic particle in the nucleus of all atoms.
  27. Radioactive decay
    Natural, inevitable process by which an atom emits energy as subatomic particles and x-rays as its unstable nucleus spontaneously breaks apart; transforms one element into another in a predictable time span.
  28. Radioisotopes
    Any isotope that has an unstable nucleus.
  29. Salt
    Any compound that releases ions other than H+ and OH- in solution.
  30. Shell model
    Model for how electrons are distributed in an atom; all of the orbitals are shown as a nested series of shells.
  31. Solute
    [L. solvere, to loosen] Any substance dissolved in a solution.
  32. Solvent
    Any fluid (e.g., water) in which one or more substances are dissolved.
  33. Sphere of hydration
    A clustering of water molecules around molecules or ions of a solute by positive and negative interactions.
  34. Temperature
    Measure of molecular motion.
  35. Tracers
    Any substance with a radioisotope attached; researchers can track it after delivering it into a cell, a multicelled body, ecosystem, or some other system.