Periodic trends

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This is a short presentation on the trends found in the periodic table.

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Periodic trends

  1. 1. Objectives <ul><li>Define atomic and ionic radii, ionization energy, electron affinity, and electronegativity. </li></ul><ul><li>Compare the periodic trends of atomic radii, ionization energy, and electronegativity, and state the reasons for these variations. </li></ul><ul><li>Define valence electrons, and state how many are present in atoms of each main-group element. </li></ul>Section 2 Periodic Trends
  2. 2. Atomic Radii <ul><li>The boundaries of an atom are fuzzy, and an atom’s radius can vary under different conditions. </li></ul><ul><li>To compare different atomic radii, they must be measured under specified conditions. </li></ul><ul><li>Atomic radius - one-half the distance between the nuclei of identical atoms that are bonded together. </li></ul>Section 2 Periodic Trends
  3. 3. Atomic Radii Section 2 Periodic Trends
  4. 4. Atomic Radii <ul><li>Atoms tend to be smaller as you go from left to right on the periodic table. </li></ul><ul><li>This is due to increasing positive charge in the nucleus, pulling the electrons closer to the center. </li></ul><ul><li>Atoms tend to be larger down a group. </li></ul><ul><li>This trend is due to the increasing size of the electron cloud as electrons fill up larger energy levels. </li></ul>Section 2 Periodic Trends
  5. 5. Atomic Radii Section 2 Periodic Trends
  6. 6. Ion definition Section 2 Periodic Trends <ul><li>Watch the video on entitled “Ion definition” found in this section of the course </li></ul>
  7. 7. Ionic Radii trends Section 2 Periodic Trends
  8. 8. Ionic Radii trends Section 2 Periodic Trends <ul><li>Positive ions tend to be smaller than neutral atoms. </li></ul><ul><li>The larger the positive charge, the smaller the ion. </li></ul><ul><li>Again, this is due to increasing positive charge in the nucleus, pulling the electrons closer to the center. </li></ul>
  9. 9. Ionic Radii trends Section 2 Periodic Trends <ul><li>Negative ions tend to be larger than neutral atoms. </li></ul><ul><li>The more negative the charge, the larger the ion. </li></ul><ul><li>This is due to the repelling forces between electrons, causing them to occupy a larger space around the atom </li></ul>
  10. 10. Ionization Energy Section 2 Periodic Trends <ul><li>The process to form an ion is called ionization. </li></ul><ul><li>The energy required to remove one electron from a neutral atom is called ionization energy . </li></ul><ul><li>Sometimes refered to as IE 1 or first ionization energy . </li></ul>
  11. 11. Ionization Energy Section 2 Periodic Trends <ul><li>Ionization energies increase across a period. </li></ul><ul><li>Caused by increasing effect nuclear charge </li></ul><ul><li>Higher positive charge more strongly attracts electrons in the same energy level </li></ul>
  12. 12. Ionization Energy Section 2 Periodic Trends <ul><li>Ionization energies decrease down a group. </li></ul><ul><li>Electrons removed from larger atoms are at higher energy levels, and are farther away from the nucleus. </li></ul><ul><li>Electrons are removed more easily due to their distance from the nucleus. </li></ul>
  13. 13. Ionization Energy Section 2 Periodic Trends
  14. 14. Ionization Energy Section 2 Periodic Trends <ul><li>Watch the “Ionization” in this lesson when you get to this slide before continuing. </li></ul>
  15. 15. Electron affinity Section 2 Periodic Trends <ul><li>The energy change that occurs when an electron is acquired by a neutral atom is called electron affinity. </li></ul><ul><li>Electron affinity generally increases across periods. </li></ul><ul><li>Electron affinity generally decreases down groups. </li></ul><ul><li>All these can be explained by effective nuclear charge and by the distance of an electron from the nucleus. </li></ul>
  16. 16. Electron Affinity Section 2 Periodic Trends <ul><li>Watch the video on “Electron Affinity” that is included in this lesson. </li></ul>
  17. 17. Valence electrons Section 2 Periodic Trends <ul><li>Compounds form because electrons are lost, gained, or shared between atoms. </li></ul><ul><li>Electrons involved in this behavior are called valence electrons. </li></ul><ul><li>Valence electrons are the outermost energy level electrons in an atom. </li></ul><ul><li>Atoms tend to want to have a full set of 8 valence electrons to be stable. </li></ul>
  18. 18. Valence electrons Section 2 Periodic Trends <ul><li>Watch the video on “Valence electrons” included in this lesson. </li></ul>
  19. 19. Electronegativity Section 2 Periodic Trends <ul><li>Valence electrons hold atoms together in compounds. </li></ul><ul><li>In many compounds, the negative charge of the electrons is concentrated closer to one atom than another. </li></ul>
  20. 20. Electronegativity Section 2 Periodic Trends <ul><li>Electronegativity is the ability of an atom in a compound to attract electrons from another atom in the compound. </li></ul><ul><li>Electronegativity generally increases across rows, and decreases down a group </li></ul>
  21. 21. Electronegativity Section 2 Periodic Trends <ul><li>Watch the video on “Electronegativity” found in this lesson. </li></ul>
  22. 22. Summary of periodic trends Section 2 Periodic Trends

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