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Valence Electrons

Valence Electrons. The electrons responsible for the chemical properties of atoms are those in the outer energy level. Valence electrons - The electrons in the outer energy level or shell the highest occupied energy level Inner electrons -those in the energy levels below.

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Valence Electrons

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  1. Valence Electrons • The electrons responsible for the chemical properties of atoms are those in the outer energy level. • Valence electrons - The electrons in the outer energy level or shell • the highest occupied energy level • Inner electrons -those in the energy levels below.

  2. Keeping Track of Electrons • Atoms in the same column... • Have the same outer electron configuration. • Have the same valence electrons. • Easily found: same as the main group number on the periodic table. • Group 2: Be, Mg, Ca, Sr, Ba. • 2 valence electrons

  3. Electron Dot diagrams • A way of keeping track of valence electrons. • How to write them? • Write the symbol. • Put one dot for each valence electron • Don’t pair up until they have to. X

  4. The Electron Dot diagram for Nitrogen • Nitrogen has 5 valence electrons. • First we write the symbol. N • Then add 1 electron at a time to each side. • Until they are forced to pair up.

  5. Electron Configurations for Cations • Metals lose electrons to attain noble gas configuration (full outer shell). • They make positive ions (cations) • If we look at the electron configuration, it makes sense to lose electrons: • Na 2,8,1 1 valence electron • Na+2,8 noble gas configuration

  6. Electron Dots For Cations • Metals will have few valence electrons (usually 3 or less) Ca

  7. Electron Dots For Cations • Metals will have few valence electrons • These will come off Ca

  8. Electron Dots For Cations • Metals will have few valence electrons • These will come off • Forming positive ions Ca2+ noble gas configuration

  9. Electron Configurations for Anions • Nonmetals gain electrons to attain noble gas configuration. • They make negative ions (anions) • Halide ions- ions from chlorine or other halogens that gain electrons • S (2,8,6) - 6 valence electrons • S2- (2,8,8) - a noble gas configuration.

  10. Electron Dots For Anions • Nonmetals will have many valence electrons (usually 5 or more) • They will gain electrons to fill outer shell. P P3-

  11. Stable Electron Configurations • All atoms react to achieve noble gas configuration. • Noble gases have 8 outer shell (valence) electrons. • This is also called the octet rule. Ar

  12. Ionic Bonding • Between metals and non-metals • Transfer of electrons • Full outer shells • Oppositely charged ions created • Ions held to one another by electrostatic attraction • Giant structure formed

  13. Ionic Bonds Characteristics of ionic compounds • Usually soluble in water • Electrical conductors when molten and when in aqueous solution. • High m.p. • Brittle, hard crystals

  14. Ionic Bonding • Anions and cations are held together by opposite charges. • Ionic compounds are called salts. • Simplest ratio is called the formula unit. • The bond is formed through the transfer of electrons. • Electrons are transferred to achieve noble gas configuration.

  15. Ionic Bonding Na Cl

  16. Ionic Bonding Na+ Cl-

  17. Ionic Bonding • All the electrons must be accounted for Ca P

  18. Ionic Bonding Ca P

  19. Ionic Bonding Ca2+ P

  20. Ionic Bonding Ca2+ P Ca

  21. Ionic Bonding Ca2+ P 3- Ca

  22. Ionic Bonding Ca2+ P 3- Ca P

  23. Ionic Bonding Ca2+ P 3- Ca2+ P

  24. Ionic Bonding Ca Ca2+ P 3- Ca2+ P

  25. Ionic Bonding Ca Ca2+ P 3- Ca2+ P

  26. Ionic Bonding Ca2+ Ca2+ P 3- Ca2+ P 3-

  27. Ionic Bonding = Ca3P2 Formula Unit Calcium Phosphide

  28. Classwork problems (a) Show the bonding between the following • Magnesium and Oxygen • Potassium and Chlorine • Calcium and Fluorine • Lithium and Nitrogen • Aluminium and Fluorine

  29. Properties of Ionic Compounds • Crystalline structure, usually solids • A regular repeating arrangement of ions in the solid • Ions are strongly bonded together. • Structure is rigid. • High melting points • Electrical conductors when melted • Electrical conductors in solution

  30. Crystalline structure

  31. Conducting electricity • Conducting electricity is allowing charges to move. • In a solid, the ions have charges but are locked in place. • Ionic solids are insulators. • When melted, the charged ions can move around. Melted ionic compounds conduct electricity. • To melt NaCl, it must get to about 800 ºC. • Dissolved in water (aqueous) the ions are now free to move and they conduct electricity.

  32. + - + - - + - + + - + - - + - + Ionic solids are brittle

  33. - + - + - + - + + - + - - + - + Ionic solids are brittle • Displacing the top layer (diagram) puts ions of the same charge near one another creating strong repulsion that breaks the crystal apart.

  34. Solubility • Ionic solids are often (but not always) soluble in water. • Solubility usually (but not always) increases with increasing temperature.

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