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Predicting Charge from the Periodic Table

Predicting Charge from the Periodic Table. Energy & Stability. Rubberbands Springs Kleenex box Popper High Energy means Low Stability. Low Energy means High Stability. Memory Jogger. Stability in Chemical Systems. If it exists, it’s stable!

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Predicting Charge from the Periodic Table

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  1. Predicting Charge from the Periodic Table

  2. Energy & Stability • Rubberbands • Springs • Kleenex box • Popper High Energy means Low Stability. Low Energy means High Stability. Memory Jogger

  3. Stability in Chemical Systems • If it exists, it’s stable! • Of course, some things are more stable than others.

  4. Noble Gases – What they tell us • Group 18 or Group VIIIA or Group O. • Do not form compounds under ordinary conditions. They are extremely stable. • All have 8 valence electrons: great stability. Must also be low energy!

  5. Why do atoms gain or lose electrons? • They are trying to get the structure of the nearest noble gas! • What’s the nearest noble gas to • F • Na • S • Mg • H Memory Jogger Ne – the F adds 1 electron It’s still Ne – the Na loses 1 electron Ar – the S adds 2 electrons Ne – the Mg loses 2 electrons He – the H adds 1 electron

  6. Octet Rule • When we say that atoms are trying to get an octet, we mean … They are trying to attain the electron structure of the nearest noble gas. Strictly speaking, H wants only a duet.

  7. Lewis Structures of Atoms • Use dots around the symbol to represent the valence electrons. • What’s the Lewis structure for Cl? • For Ca? Memory Jogger : .Cl: : · Ca·

  8. p-block s-block

  9. Gain or Lose? • Atoms form ions to get to the nearest noble gas configuration. • Metals tend to have 1, 2, or 3 valence electrons. It’s easier to lose 1, 2, or 3 than gain 5, 6, or 7. • Remember – it’s all or nothing!

  10. Metals: Atoms to Ions • Na: 2-8-1  2-8-0, Na+1 • K: 2-8-8-1  • Mg: 2-8-2  • Al: 2-8-3  • Ca: 2-8-8-2  • Cs: 2-8-18-18-8-1 2-8-8-0, K+1 2-8-0, Mg+2 2-8-0, Al+3 2-8-8-0, Ca+2 2-8-18-18-8-0, Cs+1

  11. Lewis Structures for Positive Ions Na atom, 2-8-1: Na· Na+1, 2-8-0: [Na]+1 • The ions always have square brackets and a charge. • Lewis diagram of the ion has to reference the same shell as the Lewis diagram of the atom.

  12. Mg atom, 2-8-2 Mg. Mg+2, 2-8-0 [Mg]+2 Al atom, 2-8-3 Al· Al+3, 2-8-0 [Al]+3 Lewis Structures for Positive Ions . · · What do they have in common? No Dots!

  13. Gain or Lose? • Nonmetals tend to have 5, 6, or 7 valence electrons. It’s easier to add 1, 2, or 3 than lose 5, 6, or 7.

  14. Nonmetals: Atoms to Ions • S: 2-8-6  2-8-8, S-2 • F: 2-7  • N: 2-5  • Br: 2-8-18-7  • Se: 2-8-18-6  • P: 2-8-5  2-8, F-1 2-8, N-3 2-8-18-8, Br-1 2-8-18-8, Se-2 2-8-8, P-3

  15. Lewis Structures for Negative Ions : F atom, 2-7: .F: F-1, 2-8: [:F:]-1 Try S-2 and N-3 What do they have in common? : : : 8 DOTS!

  16. Noble Gases • They already have 8 valence electrons, except He which has 2. • They don’t form ions very easily.

  17. How many valence electrons • Group 1 or IA • Group 2 or IIA • Group 13 or IIIA • Group 14 or IVA • Group 15 or VA • Group 16 or VIA • Group 17 or VIIA • Group 18 or VIIIA

  18. Ba Te I Rb Sr O Kr Cs Ra Br N B Predict Likely Charges 0 +2 +1 -2 +2 -1 -1 +1 -3 +2 -2 +3

  19. Ionic Size Relative to Parent Atom • Depends on if it’s a positive ion or a negative ion. • How do you make a positive ion? • How do you make a negative ion? Remove electrons Add electrons

  20. Size of Ions • Positive ion - smaller than the parent atom. • Not only do you remove electrons, you wipe out a whole shell! • Negative ion – larger than the parent atom. • Trying to jam an extra electron into the cloud. Adds lots of repulsions.

  21. Metals are losers! • Metals lose electrons to form positive ions or cations. • Cations are always smaller than the parent atom.

  22. Nonmetals are winners! • Nonmetals gain electrons to form negative ions or anions. • Anions are always larger than the parent atom.

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