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Periodic Groups and Trends

Periodic Groups and Trends. Periodic Table. Periodicity: regular variations (or patterns) of properties with increasing atomic weight. Both chemical and physical properties vary in a periodic (repeating pattern). Group: vertical column of elements (“family”)

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Periodic Groups and Trends

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  1. Periodic Groups and Trends

  2. Periodic Table • Periodicity: regular variations (or patterns) of properties with increasing atomic weight. Both chemical and physical properties vary in a periodic (repeating pattern). • Group: vertical column of elements (“family”) • Period: horizontal row of elements

  3. Activity: get out your black and white copy of the periodic table.

  4. On one side, color and label the metals, nonmetals, and metalloids. Another name for “metalloid” is “semi-metal”.

  5. Color and label the groups/families of elements on the other side of your paper. Remember to create a legend. noble gases Transition metals alkali metals halogens alkaline earth metals lanthanides actinides

  6. PERIODIC GROUPS • alkali metals • alkaline earth metals • transition metals • halogens • noble gases • lanthanides • actinides

  7. Alkali Metals • Group 1 on periodic table • Very reactive • Soft solids • Readily combine with halogens (ex. NaCl) • Tendency to lose one electron (to become an ion)

  8. Alkaline Earth Metals • Group 2 on periodic table • Abundant metals in the earth • Not as reactive as alkali metals • Higher density and melting point than alkali metals

  9. Transition Metals • Groups 3-12 on periodic table Important for living organisms (think vitamins: multivitamins (they have iron, zinc, chromium, etc.)

  10. Halogens • Group 7A on periodic table (***or GROUP 17) • “Salt former” – combines with groups 1 and 2 to form salts (ionic bonds)

  11. Noble Gases • Group 8 on periodic table (** or GROUP 18) • Relatively inert, or nonreactive • Gases at room temperature

  12. Lanthanides • Part of the “inner transition metals” • Soft silvery metals • Tarnish readily in air • React slowly with water

  13. Actinides • Radioactive elements • Part of the “inner transition metals”

  14. PERIODIC TRENDS • Atomic radii • Ionization energy • Ionic radii • Electronegativity

  15. Atomic Radii

  16. Atomic Radii • Trend: increases down a group • WHY??? • The atomic radius gets bigger because electrons are added to energy levels farther away from the nucleus. • Plus, the inner electrons shield the outer electrons from the positive charge (“pull”) of the nucleus; known as the SHIELDING EFFECT

  17. Atomic Radii • Trend: decreases across a period • WHY??? • As the # of protons in the nucleus increases, the positive charge increases and as a result, the “pull” on the electrons increases.

  18. Ionization Energy • Definition: energy required to remove outer electrons

  19. Ionization Energy • Definition: energy required to remove outer electrons

  20. Ionization Energy • Trend: decreases down a group • WHY??? • Electrons are in higher energy levels as you move down a group; they are further away from the positive “pull” of the nucleus and therefore easier to remove.

  21. Ionization Energy • Trend: increases across a period • WHY??? • The increasing charge in the nucleus as you move across a period exerts greater “pull” on the electrons; it requires more energy to remove an electron.

  22. Ionic Radii • Cations are always smaller than the metal atoms from which they are formed. (fewer electrons because metals LOSE electrons) • Anions are always larger than the nonmetal atoms from which they are formed. (more electrons because nonmetals GAIN electrons)

  23. Electronegativity • Definition: the tendency of an atom to attract electrons to itself when chemically combined with another element

  24. Electronegativity • Trend: decreases down a group • WHY??? • Although the nuclear charge is increasing, the larger size produced by the added energy levels means the electrons are farther away from the nucleus; decreased attraction, so decreased electronegativity; plus, shielding effect

  25. Electronegativity • Trend: increases across a period (noble gases excluded!) • WHY??? • Nuclear charge is increasing, atomic radius is decreasing; attractive force that the nucleus can exert on another electron increases.

  26. Summing Up Periodic Trends

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