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Electron-Dot Notation

Electron-Dot Notation. How does the interaction between nuclei & valence electrons affect how atoms interact together?. Electron-Dot Notation. Valence electrons are responsible for chemical bonding. Group 1: Alkali metals have 1 valence electron

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Electron-Dot Notation

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  1. Electron-Dot Notation How does the interaction between nuclei & valence electrons affect how atoms interact together?

  2. Electron-Dot Notation • Valence electrons are responsible for chemical bonding. • Group 1: Alkali metals have 1 valence electron • Group 2: Alkali-earth metals have 2 valence electrons • Electron-Dot Notation: • It only shows the valence electrons of an atom, which are indicated by dots placed around the element’s symbol.

  3. X Electron-Dot Notation • Write the symbol • Put one dot for each valence electron. • Don’t pair up the e- unless you have to.

  4. Electron Dot Notation: 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. Write the electron dot notation for…Remember:# Valence Electron = # electrons on outermost ring (last ring) • Na • Mg • C • O • F • Ne • He Na 1s22s22p63s1 Mg 1s22s22p63s2 C 1s22s22p2 O 1s22s22p4 F 1s22s22p5 Ne 1s22s22p6 He 1s2

  6. Electron-Dot Notation: Cations • Metals (L side of the Periodic Table) tend to lose electrons to attain greatest stability (8 valence electrons – Octet Rule). • This results in forming positive ions, cations. Example: Na 1s22s22p63s1 - 1 valence electron Na+ 1s22s22p6 – 8 valence electrons

  7. 20 Ca 40.078 Electron Dot Notation for Cations • Elements that have few valence electrons will tend to lose them, forming positive ions: cations. Calcium: 20 e- Ca2+: 18 e- 1s22s22p63s23p64s2 1s22s22p63s23p6 Ca2+ Ca

  8. Electron Configurations for Anions • Nonmetals (R of the periodic table) tend to gain electrons to attain stability • This results in forming negative ions, anions. Sulfur • S 1s22s22p63s23p4 - 6 valence electrons • S2- 1s22s22p63s23p6– 8 valence electrons S2- S

  9. Common Monatomic Ions: pg. 221

  10. Elements down a group have similar charges. • Group 1 (Alkali) elements produce 1+ ions • Group 2 (Alkali-earth)elements produce 2+ ions • Group 13 elements produce 3+ ions

  11. Group 14 elements produce 4- ions • Group 15 elements produce 3- ions • Group 16 elements produce 2- ions • Group 17 (Halogens) elements produce 1- ions • Group 18 (noble gases) elements (STABLE!) – do not produce ions

  12. Ionic Bonding & Ionic Compounds

  13. Ionic Bonding • Ionic Compounds: Composed of a cation and an anion that are bonded together • Ionic compounds are called salts.

  14. Properties of Ionic Compounds: Crystal Lattice • Ionic Compounds consists of positive and negative ions held together by ionic bonds. • They are ordered in a rigid structure, called a crystal lattice. • Crystal Lattice: a repeating arrangement of ions in the solid. • Ionic compounds have high melting points - because of strong forces between ions • It requires a lot of energy to melt an ionic compound

  15. Table salt Crystal Lattice: Table Salt, NaCl Ionic Bonding - Crystal Lattice

  16. - + - + + - + - - + - + + - + - - + - + Ionic solids are Brittle Strong repulsion breaks crystal apart. Force

  17. Ionic Bonding • Ionic Bonding: Formed when atoms completely give up electrons to other atoms, transferring of electrons.. • To achieve stability  8 valence electrons.

  18. - + Ionic Bonding • Example: Sodium & Chloride • Sodium: Group 1, 1 valence electron • Chloride, Group 17, 7 valence electrons • Sodium will give up its 1 valence electron so that it can achieve stability, meanwhile chlorine gains 1 to achieve stability • Mutual Benefits! transfer of electron Na Cl NaCl

  19. n = 3 n = 3 Ionic Bonding NaCl - n = 2 - - - - - - - - - - - - - - - - - - - - - - - - - + - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Na 1 valence electron Cl 7 valence electrons Na+ 8 valence e- Cl- 8 valence electrons Transfer of electrons to achieve a stable octet (8 electrons in valence shell).

  20. Calcium gives up two valence electrons – one to each fluorine atom.

  21. Chemical Formulas • Chemical Formulas indicate the number of atoms of each kind in a compound. CaCl2 • Binary Compound: Two Types of atoms Calcium Chloride 2 Chloride atoms 1 Calcium atom “Chlorine” becomes ‘Chloride” when it gains electrons Cations always come first

  22. Formulating Binary Ionic Compounds: Criss-Cross Rule Steps 1. Write out names with space Calcium Chloride 2. Write symbols & charge of elements 3. criss-cross charges as subscripts, drop the + and - signs 2+ Ca Cl 1- 4. combine into formula (“1” is never shown) Ca Cl 1 2 CaCl2

  23. Criss-Cross Rule: Aluminum Oxide Note: The name of the cation is given first, then the anion. Step 1: Aluminum Oxide Step 2: Al3+ O2- Step 3: Al O 2 3 Step 4: Al2O3

  24. Criss-Cross Rule: Magnesium Oxide Step 1: Magnesium Oxide Step 2: Mg2+ O2- Step 3: Mg O 2 2 Step 4: Mg2O2 Step 5 MgO (Reduce to lowest terms) :

  25. Criss-Cross Rule Criss-cross rule: ** Warning: Reduce to lowest terms. Ir3+ and Br1– Al3+ and O2– Ba2+ and S2– Ir1 Br3 Al2 O3 Ba2 S2 Al2O3 BaS IrBr3

  26. Ionic Bonding Ca +2 Ca P -3 +2 Ca P -3 +2 • All the electrons must be accounted for!

  27. P3- P 3- Ca2+ Ca2+ Ca2+ Ionic Bonding Ca2+ Ca3P2 Ca2+ P3- Ca2+ Formula Unit P3-

  28. Polyatomic Ions • Ionic bonding can occur with polyatomic ions, because sometimes, a cation or an anion can be a polyatomic ion…which is - • A charged group of atoms, resulting from an excess of electrons ( - ) or a shortage of electrons (+) • Stays together, functions as a unit

  29. Common Polyatomic Ions

  30. Writing Formulas with Polyatomic Ions

  31. Binary Compounds: Formulas • http://www.chemfiles.com/flash/formulas.html

  32. Bonding Activity – Why the criss-cross rule?

  33. Br1- Br1- Br Br K e- e- Br1- Br1- bromine atom potassium atom e- O2- potassium ion bromide ion Mg2+ K1+ K1+ K1+ K1+ K bromine atom potassium atom bromide ion potassium ion potassium bromide KBr magnesium bromide potassium oxide MgBr2 K2O

  34. Br1- Br1- Br1- PO43- O2- N3- Al3+ Ca2+ Pb4+ Mg2+ S2- K1+ K1+ K1+ OH1- OH1- NH41+ NO31- ? Cu2+

  35. Review: Naming Ionic Compounds

  36. Rules of Naming Ionic Compounds • The name of cations do not change. Examples: Sodium, Na+ Hydrogen, H+ • The ending of monatomic anions change to –ide. Examples: Chlorine  Chloride, Cl- Nitrogen  Nitride, N3- • The name of polyatomic ions do not change. Examples: Bromate, BrO3-Carbonate, CO32-

  37. Rules of Naming Ionic Compounds • Some cations have multiple charges. These are represented by roman numerals. • This system of naming is called the Stock system. Examples: Lead (IV): Pb4+ Lead (II): Pb2+ Lead(IV) oxide vs. Lead (II) oxide Pb4+ O2- Pb2+ O2- Pb2O4 Pb2O2 PbO2 PbO We must use the Stock system to distinguish which lead we are referring to.

  38. Nomenclature: Binary Compounds – Stock System

  39. Practice: Formula Name barium oxide • BaO ____________________ • ________________ sodium bromide • MgI2 ____________________ • KCl ____________________ • ________________ strontium fluoride • ________________ cesium fluoride NaBr magnesium iodide potassium chloride SrF2 CsF

  40. Practice: Which iron is used in these chemical formula? • Fe2O3 Iron(III) oxide • FeS Iron(II) sulfide Which copper is used in this chemical formula? • Cu(ClO4)2 Copper(II) perchlorate Which gold is used in this chemical formula? Au2O

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