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Bonding Between Atoms

Bonding Between Atoms. Why do Atoms Form Bonds?. To get a stable octet of valence electrons. Called a “noble gas configuration”. Changes in Energy. Energy is released when bonds form. (exothermic) Results in lower energy, more stability Know example…. Bonding Type #1. Ionic Bonding.

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Bonding Between Atoms

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  1. Bonding Between Atoms

  2. Why do Atoms Form Bonds? • To get a stable octet of valence electrons. • Called a “noble gas configuration”

  3. Changes in Energy • Energy is released when bonds form. (exothermic) • Results in lower energy, more stability • Know example…

  4. Bonding Type #1 Ionic Bonding

  5. Atoms Become Ions • Metals Lose Electrons: • become a (+) ion (cation) • Ex: Mg is 2-8-2 • Loses 2 electrons to become Mg+2 2-8 • Nonmetals Gain Electrons: • become a (–) ion (anion) • Ex: Cl is 2-8-7 • Gains 1 electron to become Cl-1 2-8-8

  6. Electron Transfer • As ions form, an exchange or transfer of electrons happens. Lithium (metal) 2-1 Fluorine (nonmetal) 2-7

  7. Electronegativity • Atoms in ionic compounds have large differences in their EN values ( > 1.7)

  8. Ex: EN Values • Metal Na = 0.9 • Nonmetal Cl = 3.2 • Nonmetal with higher EN “takes” electron(s) from the metal • The greater the EN difference, the more “Ionic Character”.

  9. A positively charged ion and a negatively charged ion attract each other. • This attraction forms an IONIC BOND - ion + ion

  10. Ionic compounds have a uniform crystalline lattice structure.

  11. Classic Example of Ionic Bond Formation • http://youtu.be/xTx_DWboEVs

  12. Drawing Lewis Dot Diagrams of Atoms, Ions and Ionic Compounds

  13. Properties of Ionic Compounds

  14. High Melting Point Attraction between the ions is very strong. Requires a lot of heat energy to separate ions and make solid crystal melt.

  15. Solubility in Water • Most ionics will dissolve in water, or be “soluble”. • When dissolved in water they are “aqueous” Ex: NaCl (aq)

  16. Water is a “polar molecule”. • Acts like a magnet to pull ions apart and into solution. • Ions are now “dissociated” or “hydrated” ions. • http://youtu.be/EBfGcTAJF4o

  17. Conductivity • Ionic compounds conduct when ions are “mobile” or free to move about.

  18. Conductivity • Ionic compounds conduct when: • Molten (melted/liquid) (l) • Aqueous (aq) Note: They DO NOT conduct when solid as the ions are locked in place.

  19. Types of Ionic Compounds • Binary: Contain ions of 2 elements Ex: MgCl2, Al2O3, NaCl

  20. Naming Binary Ionics • Name metal • Name nonmetal with “-ide” ending.

  21. Ternary: Contain 3 elements • Polyatomic ion present. • Contain both ionic and covalent bonds!! Ex: NaNO3, Ca3(PO4)2, NH4Cl Elements inside the polyatomic ion are covalently bonded (all nonmetals).

  22. Naming Ternary Ionics (with polyatomic) • Name Metal • Name polyatomic ion • If two polyatomics, name them both

  23. Ionic Compounds are Neutral Subscripts show ratio of ions Total positive and negative charges must balance so the compound is electrically neutral.

  24. Balance Formula Using Criss-Cross Method • Criss-Cross charges if necessary to balance the formula • Put parenthesis around polyatomic ions if more than one in formula

  25. When to Use a Roman Numeral • A Roman numeral is used when the metal can have more than one possible charge. • The Roman numeral indicates the charge the metal takes in that compound Ex: NiBr2 Nickel II Bromide NiBr3 Nickel III Bromide

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