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The Periodic Table of Elements - General Biology Context

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  • Who created the first coherent periodic table of elements?
    Dmitri Mendeleev in 1869, arranging elements by increasing atomic mass and leaving blank spaces for undiscovered elements.
  • How are elements arranged in the modern periodic table?
    Elements are arranged in ascending order of atomic number in 18 columns (groups) and 7 rows (periods).
  • What defines a chemical family in the periodic table?
    A chemical family corresponds to a column where elements share the same valence electron configuration.
  • What is the valence electron configuration of alkali metals?
    Alkali metals have a valence configuration of ns1 and tend to form +1 cations.
  • What are the main characteristics of alkaline earth metals?
    They have a saturated s subshell ns2 and form +2 cations; highly reactive and not found free in nature.
  • Which group contains the halogens and what is their valence configuration?
    Group 17 elements with ns2 np5 valence electrons, tending to gain one electron to form -1 anions.
  • What is special about noble gases in the periodic table?
    Noble gases have saturated outer subshells (ns2 np6), making them very stable and mostly inert.
  • What are the four blocks of the periodic table based on electron subshells?
    s-block, p-block, d-block (transition metals), and f-block (lanthanides and actinides).
  • How does atomic radius change across a period and down a group?
    Atomic radius decreases across a period due to increasing nuclear charge and increases down a group due to added electron shells.
  • How do ionic radii compare to atomic radii?
    Cations are smaller than their atoms; anions are larger than their atoms due to electron loss or gain.
  • What is ionization energy (EI)?
    The minimum energy required to remove an electron from a gaseous atom or ion.
  • How does ionization energy vary in the periodic table?
    Ionization energy increases across a period and decreases down a group, generally opposite to atomic radius trends.
  • What is electron affinity (EA)?
    The energy change when an atom gains an electron; reflects the atom's ability to form an anion.
  • Which elements have the highest electron affinities?
    Halogens have the highest electron affinities because they form stable anions isoelectronic with noble gases.
  • What is electronegativity?
    The tendency of an atom to attract electrons in a covalent bond.
  • How does electronegativity vary in the periodic table?
    Electronegativity increases across a period and decreases down a group.
  • What is the Mulliken scale of electronegativity?
    Electronegativity proportional to the average of ionization energy and electron affinity.
  • What is the Pauling scale of electronegativity?
    Based on bond energies; fluorine is assigned the highest value of 4.0.
  • How is metallic character defined in the periodic table?
    Elements whose oxides are basic and soluble in acid are metals; metallic character decreases with increasing electronegativity.
  • What is the redox character of metals and non-metals?
    Metals tend to be reducing agents (electron donors); non-metals tend to be oxidizing agents (electron acceptors).