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Chemical Bonding

This article provides an introduction to chemical bonding, explaining the different types of bonds (ionic, covalent, and metallic) and their properties. It also covers Lewis structures and electron transfer diagrams.

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Chemical Bonding

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  1. Chemical Bonding

  2. Introduction to Bonding

  3. Neutral or “free” atoms are rarely found in nature • Most elements exist as part of a compound • Compounds are chemically bonded atoms

  4. Chemical bond: strong attractive force that exists between atoms or ions in a compound.

  5. So, why do atoms form bonds?

  6. Atoms form bonds to become more stable.

  7. Bonding involves only valenceelectrons

  8. Remember… • The noble gases are particularly stable because their outer shell is full of electrons (usually 8)

  9. Octet Rule: • Atoms tend to gain, lose, or share electrons until they are surrounded by eight valence electrons(noble gas configuration)

  10. Types of Chemical Bonds • Ionic • Valence electrons are transferredfrom one atom to another. • Usually formed between a metal and a non-metal.

  11. This creates + ions and - ions which are then electrostatically attracted.

  12. 2. Covalent • Pairs of electrons areshared between atoms. • Usually formed between two non-metals.

  13. Two Types of Covalent Bonds A. Polar Covalent • Electrons are sharedunequally. • Usually between two different nonmetals.

  14. B. Non-Polar Covalent • Electrons are sharedequally. • Usually between atoms of the same element.

  15. Metallic • attraction between a metallic cation and delocalized electrons. • Delocalized electrons – valence electrons not held by any specific atom, but free to move from one atom to another. • “Electron Sea” • Usually formed between metals.

  16. Bond Properties ionic vs.covalent • formula unit (NaCl) molecule (CO2) • hard & brittle pliable • soluble in H2O PC: soluble in H2O NPC: insoluble in H2O

  17. Bond Properties ionic vs. covalent • high melting & low melting & boiling points boiling points • electrolytes non-electrolytes • electron Lewis structures transfer diagrams

  18. Formula unit • ionic compounds are not found as single molecules. • the simplest ratio of cations to anions • Example: ZnCl2represents the simplest combination of zinc and chlorine: one Zn 2+ ion and two Cl- ions

  19. WATER • Contains polar covalentbonds. • Called the “universal solvent” “Like dissolves like”.

  20. Properties of Metals • Luster • High density • Good heat conductor • Good electrical conductor • High melting/boiling points • Malleable & Ductile

  21. Calculating Bond Type

  22. Very few bonds are purely one type. • The degree to which bonds are ionic or covalent can be estimated by comparing their electronegativities.

  23. Remember: Electronegativity: the tendency of an atom to attract electrons to itself when chemically bonded to other atoms.

  24. Remember: Electronegativity • Increases as you move from left to right across PT • Decreasesas you move from top to bottom on periodic table

  25. To Calculate Bond Type: • Look up values on Table of Electronegativities. • Subtract. • Locate difference on Bond Type Chart.

  26. Bond Type Chart % ionic character 100% 50% 0.5% 0.0% 4.0 1.7 0.3 0.0 ionic polar nonpolar covalent covalent

  27. Examples • Ca and Br

  28. O and O

  29. H and S

  30. IONIC BONDS

  31. Ionization: formation of an ion by the loss or gain of one or more valence electrons.

  32. Cations: positive ions formed by the loss of one or more valence electrons. • Metals tend to form cations.

  33. 2) Anions: negative ions formed by the gainof one or more valence electrons • Non-metals tend to form anions.

  34. Remember: Oxidation Numbers tell you how many valence electrons an atom will lose or gain to become stable.

  35. We use Electron Transfer Diagramsto represent ionic bonds

  36. To write Electron Transfer Diagrams: Use equation format: • Left of arrow: show electron dot diagrams • Right of arrow: show ions formed and coefficients to give proper ion ratio

  37. Stop and do the Examples

  38. COVALENT BONDS

  39. Remember: • Covalent bonds are usually formed between non-metals

  40. We use Lewis Structuresto represent covalentbonds

  41. Understanding Lewis Structures • Element symbols represent the nuclei and core electrons.

  42. Element symbols represent nuclei and core electrons • Dashes between symbols represent shared pairs of electrons • Dot pairs around the outside of a symbol represent unshared electrons

  43. Single bond = 1 dash • Double bond = 2 dashes • Triple bond = 3 dashes

  44. Central atom is the least electronegative atom.

  45. Multiple bonds are most common with • Carbon • Nitrogen • Oxygen

  46. To Write Lewis Structures • Count the total number of valence electrons.

  47. Choose central atom (least electronegative)

  48. Connect remaining atoms to central atom with single dash.

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