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Chapter 3 Atoms and Elements

Chapter 3 Atoms and Elements. 3.8 Periodic Trends. Valence Electrons. The valence electrons determine the chemical properties of the elements are the electrons in the outermost, highest energy level are related to the Group number of the element

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Chapter 3 Atoms and Elements

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  1. Chapter 3 Atoms and Elements 3.8Periodic Trends

  2. Valence Electrons The valence electrons • determine the chemical properties of the elements • are the electrons in the outermost, highest energy level • are related to the Group number of the element Example: Phosphorus has 5 valence electrons. 5 valence electrons P Group 5A(15) 1s22s22p63s23p3

  3. Groups and Valence Electrons All the elements in a group have the same number of valence electrons. Example: Elements in Group 2A(2) have two (2) valence electrons. Be 1s22s2 Mg 1s22s22p63s2 Ca [Ar]4s2 Sr [Kr]5s2

  4. Periodic Table andValence Electrons

  5. Learning Check State the number of valence electrons for each. A. O 1) 4 2) 6 3) 8 B. Al 1) 13 2) 3 3) 1 C. Cl 1) 2 2) 5 3) 7

  6. Solution State the number of valence electrons for each. A. O 2) 6 B. Al 2) 3 C. Cl 3) 7

  7. Learning Check State the number of valence electrons for each. A. Calcium 1) 1 2) 2 3) 3 B. Group 6A (16) 1) 2 2) 4 3) 6 C. Tin 1) 2 2) 4 3) 14

  8. Solution State the number of valence electrons for each. A. Calcium 2) 2 B. Group 6A (16) 3) 6 C. Tin 2) 4

  9. Learning Check State the number of valence electrons for each. A. 1s22s22p63s23p1 B. 1s22s22p63s2 C. 1s22s22p5

  10. Solution State the number of valence electrons for each. A. 1s22s22p63s23p13 B. 1s22s22p63s22 C. 1s22s22p5 7

  11. Electron-Dot Symbols An electron-dot symbol • indicates valence electrons as dots around the symbol of the element • of Mg shows two valence electrons as single dots on the sides of the symbol Mg ·· ·Mg ·or Mg ·or · Mg or · Mg ·

  12. Writing Electron-Dot Symbols The electron-dot symbols for • Groups 1A(1) to 4A(14) use single dots ·· Na··Mg··Al · ·C· · • Groups 5A(15) to 7A(17) use pairs and single dots. · ·· · · P· :O· ··

  13. Groups and Electron-Dot Symbols • in a group, all the electron-dot symbols have the same number of valence electrons (dots). Example: Atoms of elements in Group 2A(2) each have 2 valence electrons. 2A(2) · Be· · Mg · · Ca · · Sr · · Ba ·

  14. Learning Check  A. X is the electron-dot symbol for 1) Na 2) K 3) Al   B.  X  is the electron-dot symbol for  1) B 2) N 3) P

  15. Solution  A. X is the electron-dot symbol for 1) Na 2) K   B.  X  is the electron-dot symbol for  2) N 3) P

  16. Atomic Size • Atomic size • is described using the atomic radius • is the distance from the nucleus to the valence electrons • increases going down a group • decreases going across a period from left to right

  17. Atomic Size (continued)

  18. Atomic Radius Within A Group Atomic radius • increases going down a group

  19. Learning Check Select the element in each pair with the larger atomic radius. A. Li or K B. K or Br C. P or Cl

  20. Solution Select the element in each pair with the larger atomic radius. A. K is larger than Li B. K is larger than Br C. P is larger than Cl

  21. Ionization Energy Ionization energy • is the energy it takes to remove a valence electron from an atom in the gaseous state Na(g) + Energy (ionization) Na+(g) + e–

  22. Ionization Energy and Valence Electrons Ionization energy • decreases going down a group as the distance between the nucleus and valance electrons increases

  23. Ionization Energy The ionization energies of • metals are low • nonmetals are high

  24. Learning Check Select the element in each pair with the higher ionization energy. A. Li or K B. K or Br C. P or Cl

  25. Solution Select the element in each pair with the higher ionization energy. A. Li is higher than K B. Br is higher than K C. Cl is higher than P

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