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Unit #6 Chemical Bonds / Stoicheometry / Nomenclature

Unit #6 Chemical Bonds / Stoicheometry / Nomenclature. Chemical bond -. A strong attractive force between atoms or ions in a molecule. They can be either ionic or covalent. Ionic bond -.

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Unit #6 Chemical Bonds / Stoicheometry / Nomenclature

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  1. Unit #6 Chemical Bonds / Stoicheometry / Nomenclature

  2. Chemical bond - A strong attractive force between atoms or ions in a molecule. They can be either ionic or covalent.

  3. Ionic bond - A chemical bond formed by the electrostatic attraction between oppositely charged ions. Simply stated: it results from the transfer of electrons. • Examples: NaCl, KBr, CaCl2, Fe2O3

  4. Covalent bond - Chemical bond formed by the sharing of electrons. • Examples: H2O, CO2, C6H12O6, CH3OH Remember: the single, double, and triple bonds drawn in unit #5. They were all covalent bonds.

  5. Covalent bonds may be either of two types: 1) Polar covalent - A bond between two different atoms caused by the unequal sharing of the bonding electrons. 2) Non-Polar covalent - • A bond between two atoms caused by the "equal" sharing of the bonding electrons.

  6. Chemical bonds can occur between: Metal : Non-metal (Ionic) Ex: KI, MoS2 Non-metal : Non-metal (Covalent) Ex: O2, N2O Metals ≠ DO NOT bond with metals. • They can form mixtures more commonly called alloys.

  7. Animations of Chemical Bonds Types of Chemical Bonds (Ionic, Polar covalent, & Non-polar covalent)

  8. Make certain that you remember the three different types of elements on the periodic chart. Make sure that you remember the location of the three different types of elements on the periodic chart

  9. Electronegativity - The measure of the attraction an atom has for shared electrons. (How much an atom wants electrons.)

  10. Animation of Electronegativity The "Ups and Downs" of Electronegativity

  11. Compare the electronegativities of the elements.

  12. How to use electronegativity to predict the type of chemical bond that will form: 1) Calculate the difference in electronegativity between the two elements that are going to bond. These values are on the back of your periodic chart, as well as in various chemistry texts.

  13. How to use electronegativity to predict the type of chemical bond that will form: The difference is determined by subtracting the smaller number from the larger. • The element with the larger electronegativity will tend to have possession of (“hog”) the shared electrons more than the other element.

  14. How to use electronegativity to predict the type of chemical bond that will form: If the difference is 1.6 or greater; the bond will be ionic.

  15. Example: NaCl 3.16 Cl = Na = 0.93 Ionic Bond 2.23 =

  16. How to use electronegativity to predict the type of chemical bond that will form: If the difference is less than 1.6, and 0.4 or greater; the bond will be polar covalent.

  17. Example: CO2 O = C = 3.44 2.55 Polar Covalent Bond 0.89 =

  18. How to use electronegativity to predict the type of chemical bond that will form: If the difference is less than 0.4; the bond will be non-polar covalent.

  19. Example: Cl2 Cl = Cl = 3.16 3.16 Non-Polar Covalent Bond 0.00 =

  20. Ionic bonding Remember definition of an ionic bond: • A chemical bond formed by the electrostatic attraction between oppositely charged ions. Simply stated: it results from the transfer of electrons. When do ionic bonds occur? • When a metal bonds with a non-metal or when the difference in electronegativity is 1.6 or greater.

  21. Ionic compound - A compound composed of positive and negative ions. It is always written with the cation first, the anion second. Ionic compounds dissolve in polar solvents.

  22. Ionic bonding - Occurs when electrons are actually transferred from the outer shell (the valence shell) of one atom or molecule to the outer shell (the valence shell) of another, oppositely charged, atom or molecule. • As a result both atoms usually attain filled valence shells with noble-gas configurations. • This process of electron transfer is always exothermic.

  23. Polyatomic ion - Ionic bonding can also involve polyatomic ions. • An ion composed of 2 or more atoms. The charge is assumed to be on the entire molecule. Example: CO3-2 • (Carbonate) has the -2 charge dispersed over the entire molecule.

  24. This electron is transferred to the Chlorine ion, leaving this shell empty and the chlorine with a full shell. Na Cl 1 Sodium ion + 1 Chlorine ion yields 1 Sodium chloride molecule (an ionic compound).

  25. Animation ofIonic vs. Covalent Bonding The Formation of Sodium chloride and Dihydrogen monoxide

  26. Properties of ionic compounds: Most are: • Crystalline solids • (crystal: molecules, atoms, ions are arranged in a 3-dimensional repeating pattern.)

  27. Properties of ionic compounds: Most have: • Example: • NaCl melts at 8010C, boils at 14130C. Compare to covalent compounds (polar) NH3: melts at -77.70C, boils at -330C; (non-polar) O2: melts at -218.40C, boils at -182.960C. • Very high melting and even higher boiling points.

  28. Properties of ionic compounds: Most: • Dissolve in polar solvents (Ex: water)

  29. Properties of ionic compounds: Most: • Conduct electric current when: • In a molten state. • Dissolved in polar solvents (Ex: water).

  30. Quick review of necessary concepts: Where are the metals located on the periodic chart? Where are the non-metals located? Considering the number of valence electrons an atom has, when does an atom gain or give electron(s)? If an atom "gives" away electrons, what happens to its oxidation state (charge) and what does it become? If an atom "gains" electrons, what happens to its oxidation state (charge) and what does it become?

  31. Example 1: Ca 2 How many valence electrons does it have? Does it gain or give electrons? Gives How many does it give? 2

  32. Example 2: F 7 How many valence electrons does it have? Does it gain or give electrons? Gains How many does it gain? 1

  33. Example 3: Gallium & Iodine Can you balance the formula created by combining the above two elements? GaI3 This will lead to the next section: "Stoicheometry".

  34. Stoicheometry Balancing the charges on ions that are forming a molecule so that they add up to zero. • The total electrons gained must equal the number lost. Balancing chemical equation so the number of particles of reactants is equal to the number of particles of products.

  35. 4 Steps to "balancing" an ionic compound: Step 1: • Write the cation and the anion next to each other, leave some space between them.

  36. 4 Steps to "balancing" an ionic compound: Step 2: • Write the absolute value of the cation's charge as the subscript to the anion. (If this value is "1", you don't have to write anything.)

  37. 4 Steps to "balancing" an ionic compound: Step 3: • Write the absolute value of the anion's charge as the subscript to the cation. (If this value is "1", you don't have to write anything.)

  38. 4 Steps to "balancing" an ionic compound: Step 4: • Write the above determined subscripts in lowest terms.

  39. Write the balanced formula formed by combining the following ions: K & P Example 1:

  40. Write the balanced formula formed by combining the following ions: Al & O Example 2:

  41. Write the balanced formula formed by combining the following ions: Mo (VI) & O Example 3:

  42. Sometimes, you may have a formula and you will need to determine the charge on the cation (this occurs when naming transition element compounds). Use the following steps to achieve this goal:

  43. Transition element Elements that have "d" and "f" sub-levels. (See unit #3 if necessary to review "d & f sublevels").

  44. Transition Element Stoicheometry: Step 1: Write the formula, and separate the cation and anion with a cross.

  45. Transition Element Stoicheometry: Step 2: Multiply the charge of the anion with the subscript of the anion (this will always be a negative number); and write this number in the lower right corner of the cross.

  46. Transition Element Stoicheometry: • Write the absolute value of the number calculated above (in step 2) in the lower left corner of the cross. Step 3:

  47. Transition Element Stoicheometry: • Divide the number calculated in step 3 above by the subscript of the cation. This calculated value is the charge of the cation. Step 4:

  48. Transition Element Stoicheometry: Example 1: WS2 W S2

  49. Transition Element Stoicheometry: Example 2: CrO3 Cr O3

  50. Transition Element Stoicheometry: Example 3: MoO Mo O

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