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2010-01-27 16:17:09
Chapter 2 A

Cell Biology Chapter 2
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  1. Biology
    • Based on the principles of chemistry and physics

    • All living organisms are a collection of atoms and molecules

  2. Atoms
    • Smallest functional units of matter that form all chemical substances and that cannot be further broken down into other substances by ordinary chemical or physical means

    • Each specific type of atom is a chemical element

  3. 3 subatomic particles

    • Protons- positive, found in nucleus, same number as electrons

    • Neutrons- neutral, found in nucleus, number can vary

    • Electrons- negative, found in orbitals, same number as protons

    • Entire atom has no net electric charge - only in the chart

    • Some atoms have the same math

    • Big in the middle - Small on the outside

  4. Protons
    • Number of protons in an atom is its atomic number

    • The atomic number is also equal to the number of electrons in the atom so that the net charge is zero

  5. Periodic table
    • Organized by atomic number

    • Rows correspond to number of electron shells

    • Columns, from left to right, indicate the numbers of electrons in the outer shell

    • Similarities of elements within a column occur because they have the same number of electrons in their outer shells, and therefore they have similar chemical bonding properties

  6. Atomic mass
    • Protons and neutrons are nearly equal in mass, and both are more than 1,800 times the mass of an electron

    • Atomic mass scale indicates an atom’s mass relative to the mass of other atoms

    • Most common form of carbon has six protons and six neutrons, is assigned an atomic mass of exactly 12

    • Different from atomic #

    • Mass - All atoms put together

  7. Weight
    • Weight is derived from the gravitational pull on a given mass

    • EX:If a man who weighs 154 pounds on earth were standing on the moon, for example, he would only weigh about 25 pounds, but he would weigh 21 trillion pounds if he could stand on a neutron star. However, his mass is the same in all locations.

  8. Isotopes
    • Multiple forms of an element that differ in the number of neutrons

    • 12C contains 6 protons and 6 neutrons

    • 14C contains 6 protons and 8 neutrons

    • Atomic masses are averages of the weights of different isotopes of an element

  9. Hydrogen, oxygen, carbon, and nitrogen
    • Major atoms/elements in living organisms

    • Typically make up about 95% of the atoms in living organisms

    • Hydrogen and oxygen occur primarily in water

    • Nitrogen is found in proteins

    • Carbon is the building block of all living matter

    • Mineral elements - less than 1%

    • Trace elements - less than 0.01%

    • Essential for normal growth and function
  10. Chemical bonds and molecules
    • Molecule:2 or more atoms bonded together

    • Molecular formula

    • Contains chemical symbols of elements found in a molecule

    • Subscript indicates how many of each atom are present

    • Compound:Molecule composed of 2 or more elements

    • Molecule and Compound - composed of 2 or more elements

  11. Covalent bonds
    • Atoms share a pair of electrons

    • Occurs between atoms whose outer electron shells are not full

    • Covalent bonds are often the strongest of all chemical bonds, because the shared electrons behave as if they belong to each atom

    • Can share …

    • 1 pair of electrons – single bond H-F

    • 2 pairs of electrons – double bond O=O

    • 3 pairs of electrons – triple bond

  12. Polar covalent bonds
    • When two atoms with different electronegativities form a covalent bond, the shared electrons are more likely to be in the outer shell of the atom of higher electronegativity rather than the atom of lower electronegativity

    • Polar covalent bonds occur because the distribution of electrons around the atoms creates a polarity, or difference in electric charge, across the molecule

    • Water:Classic example of polar covalent bonds

    • Electrons tend to be in the more electronegative oxygen atom rather than either of the less electronegative hydrogen atoms

    • Molecule has partial negative charge region and a partial positive charge region

  13. Hydrogen bonds
    • Weak polar covalent bonds: H2O
    • --Represented as dashed or dotted lines
    • --Collectively, can form strong bond overall
    • --Holds DNA strands together
    • --Individually, weak bonds can form and break easily
    • --Substrate and enzyme bonding

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