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Ions

Ions. Objectives. Determine the number of valence electrons in an atom of a representative element Explain how the octet rule applies to atoms of metallic and non- metellic elements Describe how cations and anions form. Valence Electrons.

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Ions

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  1. Ions

  2. Objectives • Determine the number of valence electrons in an atom of a representative element • Explain how the octet rule applies to atoms of metallic and non-metellic elements • Describe how cations and anions form

  3. Valence Electrons • Responsible for the chemical properties of atoms and are those in the outer energy level • Valence electrons – the s and p electrons in the outer energy level • The highest occupied energy level • Core electrons – electrons in the energy levels below highest levels

  4. Keeping Track of Electrons • Atoms in the same column... • Have the same outer electron configuration. • Have the same valence electrons. • The number of valence electrons are easily determined. It is the group number for a representative element • Group 2A: Be, Mg, Ca, etc. • have 2 valence electrons

  5. Valence electrons

  6. Valence Electrons • Usually only electrons used in chemical bonds!!! • This means that only valence electrons are shown in electron dot structures • To us older generations – formerly known as Lewis Dot Diagrams

  7. Electron Dot diagrams are… • A way of showing & keeping track of valence electrons. • How to write them? • Write the symbol - it represents the nucleus and inner (core) electrons • Put one dot for each valence electron (8 maximum) • They don’t pair up until they have to X

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

  9. Practice • Draw the Electron Dot Diagrams of the following: • Carbon • Argon • Calcium • Aluminum

  10. Octet Rule • Octet • 8 valence electrons • Associated with stability of the noble gases • Exception: Helium • He is stable with 2 valence electrons

  11. Octet Rule • In 1916, Gilbert Lewis used idea of noble gases to explain why atoms form certain kinds of ions and molecules • Octet Rule – in forming compounds, atoms tend to achieve a noble gas configuration – 8 e- in outer level

  12. Cations • Metals LOSE electrons (left side remember!?) to attain a noble gas configuration • When electrons are lost the resulting ion is POSITIVE • Naming – the name of a cation is the same as element • Example: sodium and sodium cation

  13. Cation Electron Configuration • Let’s look at configuration of Sodium to explain why metals result in cations: • Na  1s22s22p63s1 1 valence e- • Na  1s22s22p6 Noble gas configuration • Same as what element? • Which element is bigger? Why?

  14. Cations • Although names are the same, many chemical differences • Sodium metal reacts explosively with water • Sodium cation is unreactive • Why?

  15. Electron Dots for Cations • Metals will have few valence electrons (usually 3 or less) • More than 3 electrons lost is rare but is seen in transition metals • Let’s look at calcium – 2 valence electrons Ca

  16. Electron Dots for Cations • Metals will have few valence electrons • Metals will lose their valence electrons Ca

  17. Electron Dots for Cations • Metals will have few valence electrons • Metals will lose their valence electrons Ca2+ • No dots are shown for the cation • Name: Calcium ion

  18. Electron Dots for Cations • Try Scandium!

  19. Electron Dots For Cations • Let’s do Silver, element #47 • Predicted configuration is: 1s22s22p63s23p64s23d104p65s24d9 • Actual configuration is: 1s22s22p63s23p64s23d104p65s14d10 Ag = Ag1+(can’t lose any more, charges of 3+ or greater are uncommon)

  20. Electron Dots for Cations • Silver cannot lose any more electrons so it does not achieve a true noble gas configuration • Instead it is called “pseudo-noble gas configuration”

  21. Anions Versus Cations • Some transition metals have multiple possible oxidation states (charges). To name them, you add a ROMAN NUMERAL after the name of the element to indicate the charge: ion

  22. Electron Dots for Anions • Non-metals gain electrons to attain noble gas configuration • This results in negative charge (anion) • Sulfur – 1s22s22p63s23p4 • 6 valence electrons • S2- - 1s22s22p63s23p6 • Noble gas configuration

  23. Naming Anions • Name of an anion is usually the name of the element but you drop last syllable and add “ide” • Chlorine anions – chloride anions • Oxygen anions – oxygen anions

  24. Electron Dots for Anions • Halide ion – ion formed from a halogen element • Non-metals have 5 or more valence electrons • They will GAIN electrons to fill outer shell P 3- Called Phosphide ion SHOW dots!

  25. Stable Electron Configurations • All atoms react to try and achieve a noble gas configuration • Noble gases have 2 s and 6 p electrons • 8 valence electrons = stable

  26. Ionic Bonds and Ionic Compounds

  27. Objectives • Explain the electrical charge of an ionic compound • Describe three properties of ionic compounds

  28. Ionic Bonding • Ionic compounds – compounds composed of cations and anions • Usually metal + non-metal • Ionic bond – electrostatic forces that hold ions together in ionic compounds • Opposite charges are attracted to each other • Transfer of electrons

  29. Naming Ionic Compounds • Metal cation first then non-metal anion with –ide ending • NaCl • LiF • In these ionic compounds there is one sodium atom for every chlorine atom

  30. Balancing Ionic Compounds • Sometimes an ionic compound will have numbers in addition to symbols • Magnesium chloride = MgCl2

  31. Formula Units • Chemical formula – shows kinds and numbers of atoms in smallest representative unit of a substance • NaCl • Formula unit – the lowest whole-number ratio of ions in an ionic compound • MgCl2

  32. Formula • AlBr3 • H2O2 • C6H12O6

  33. Ionic Bonding Lets do an example by combining calcium and phosphorus: • All the electrons must be accounted for, and each atom will have a noble gas configuration (which is stable). Ca P

  34. Ionic Bonding Ca P

  35. Ionic Bonding Ca2+ P

  36. Ionic Bonding Ca2+ P Ca

  37. Ionic Bonding Ca2+ P 3- Ca

  38. Ionic Bonding Ca2+ P 3- Ca P

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

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

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

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

  43. Ionic Bonding = Ca3P2 Formula Unit This is a chemical formula, which shows the kinds and numbers of atoms in the smallest representative particle of the substance. For an ionic compound, the smallest representative particle is called a: Formula Unit

  44. Writing a Formula • Write the formula for the ionic compound that will form between Ba2+ and Cl- • Solution: • Balance charge with + and – ions • Write the positive ion first and negative ion second • Cross charges and write number as subscripts

  45. Learning Check Write the correct formula for the compounds containing the following ions: 1. Na+, S2- 2. Al3+, Cl- 3. Mg2+, N3-

  46. Naming Compounds • Binary ionic compounds: (what is binary?) • Cation first then anion • Cation = name of the element • Ca2+ = calcium ion • Anion = root + ide • Cl- = chloride • Answer: CaCl2 is calcium chloride

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