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Chapter 4

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  1. Chapter 4 • Compounds and Their Bonds • Octet Rule and Ions • Ionic Compounds • Naming and Writing Ionic Formulas • Polyatomic Ions • Covalent Compounds • Electronegativity and Bond Polarity • Shapes and Polarity of Molecules • Attractive Forces in Compounds

  2. Evidence for the Octet Rule • Each filled shell (group 8A, noble gases) has eight valence electrons. • Noble gases tend not to react. • Stability of atom due to these eight electrons. • Atoms like sodium tend to always lose one electron. • Atoms like chlorine tend to always gain one electron.

  3. Octet Rule • Atoms in a compound will lose, gain, or share eight electrons. • Two types of compounds: Ionic and Covalent • Ionic – atoms gain or lose electrons to form ions. • Covalent – atoms share electrons

  4. Octet Rule

  5. Ionic Compounds • Metals will always lose electrons. • Group 1A metals will always lose one electron. • What is its charge (valence)? • Group 2A metals will always lose two electrons. • What is its valence?

  6. Ionic Compounds

  7. Ionic Compounds

  8. Ionic Compounds • Non-metals (in an ionic compound) will always gain electrons. • Group 7A will always gain one electron. • What is the valence of this group? • Group 6A (Oxygen and Sulfur) will always gain two electrons • What are their valences?

  9. Ionic Compounds

  10. Learning Check • Predicting charges… • What valence will Barium have? • What valence will Bromine have? • What valence will Aluminum have? • What valence will Nitrogen have?

  11. Common Valences

  12. Learning Check • Potassium (K) in a compound will • a) gain one electron • b) lose one electron • Potassium will have a valence of • a) –1 • b) +1

  13. Learning Check • Sulfur (S) in an ionic compound will • a) gain two electrons • b) lose two electrons • Sulfur will have a valence of • a) –2 • b) +2

  14. Ionic Compounds • All ionic compounds consist of both positive ions (cations) and negative ions (anions). • Why both? • Ionic compounds are always solids at room temperature with high melting points. • MP of NaCl = 801oC

  15. Ionic Compounds • An ionic formula is • always written with the cation first followed by the anion. • always electrically neutral – that means the total positive chargesmust equal the total negative charges. • always empirical – lowest whole number subscripts.

  16. Ionic Compounds • A subscript of “1” is always understood and never written. • ex) NaCl, consists of one sodium cation and one chlorine anion. • Subscripts of 2, 3, 4, etc. are added after each symbol when needed. • ex) Al2O3 consists of two aluminum cations and three oxygen anions.

  17. Ionic Compounds • Formation of an Ionic Compound using Lewis Dot symbols

  18. Learning Check • Show the formation of CaF2 and Li2S using Lewis Dot symbols.

  19. Ionic Compounds • Writing ionic formulas requires that all charges balance to make it neutral. • Ex) Al+3 , Cl-1 • +3 -1 • -1 • -1 • +3 + -3 = 0 • AlCl3

  20. Learning Check • Write formulas between each of the following ions. • Mg+2 , O-2 • Li+1 , N-3 • Sr+2 , Br-1 • Al+3 , S-2

  21. Nomenclature • Naming ionic compounds requires that you determine whether the cation (metal) has a fixed or a variable charge. • Main group metals have fixed charges. • Exception: Sn and Pb

  22. Nomenclature • Transition group metals have variable charges. • Exception: Ag and Zn • Naming an ionic compound whose cation has a fixed charge: • Name the metal (cation) first. • Name the non-metal (anion) second, but change its suffix to –ide.

  23. Nomenclature • Naming an ionic compound whose cation has a variable charge: • Determine the charge of the cation by deduction. • Name the metal (cation) first followed by its charge in (roman numerals). • Name the non-metal (anion) second, but change its suffix to –ide.

  24. Learning Check • Name the following compounds with FIXED charges. • NaBr • CaO • MgCl2 • Al2O3 • ZnF2

  25. Learning Check • Name the following compounds with VARIABLE charges. • FeCl2 • Cu2S • MnO2 • Cr2S3 • SnBr2

  26. Nomenclature • Writing formulas from a name. • Once again, an ionic compound is electrically neutral. • Must figure out how many of each ion is needed to make it neutral. • Roman numeral (if present) is that metals valence.

  27. Nomenclature • Rules: • Write the symbol for each element, including its charge. • Determine the number(s) of each ion required to produce a neutral compound. • Write the formula with the cation first and the anion second, including their subscripts.

  28. Learning Check • Write the formulas for: • sodium oxide • aluminum iodide • lead(II) sulfide • iron(III) fluoride • magnesium nitride

  29. Polyatomic Ions • A group of atoms bonded together with a net charge. • Most common: P, N, S, and C bonded from one to four oxygen atoms. • Less common: transition metals like Cr and Mn bonded to oxygen atoms. • Less common: Cl, Br, and I bonded to oxygen atoms.

  30. Polyatomic Ions Do not need to memorize these! But… being able to recognize them is ciritical! • NO3-1 = nitrate • NO2-1 = nitrite • OH-1 = hydroxide • HCO3-1 = bicarbonate • ClO3-1 = chlorate • ClO4-1 = perchlorate • MnO4-1 = permanganate • CO3-2 = carbonate • SO4-2 = sulfate • SO3-2 = sulfite • CrO4-2 = chromate • PO4-3 = phosphate • NH4+1 = ammonium

  31. Polyatomic Ions • These ions ALWAYSkeep there name. • Changing the name alters the meaning! • Ex) Na2SO4 = sodium sulfate • If you called this “sodium sulfide”, then the formula is: Na2S.

  32. Naming Compounds with polyatomic ions • Note: if the ammonium ion is present, then name it first followed by the name of the anion with the –ide suffix. • Identify the metal present as having a fixed or variable charge. • If fixed, name the metal. • If variable, name the metal followed by its charge in roman numerals.

  33. Naming Compounds with polyatomic ions • Name the polyatomic ion present – keeping its name EXACTLY the same as on the handout. • Ex) K2CO3 = • Ex) FeSO4 =

  34. Writing Formulas • Once again, all ionic formulas must have an equal number of positive and negative charges. • If more than one polyatomic ion is required, then it is put in parenthesis with a subscript outside of these.

  35. Learning Check • Name each compound. • Na3PO4 • Zn(OH)2 = • V(NO3)3 =

  36. Learning Check • Write the formulas for: • lithium nitrite • nickel(II) chlorate • aluminum sulfate

  37. Covalent Compounds • Covalent bonds form when two atoms share electrons to achieve an octet. • Simplest case is when two Hydrogen atoms form an H2 molecule. • Each atom has one electron. • Note that an “octet” for Hydrogen is two electrons.

  38. Formation of F2 • In F2 each F atom has seven valence electrons. • The odd electrons can pair up to form a bond.

  39. Formation of CH4, Methane • C has four valence electrons and each H has one. • These pair up to form four bonds.

  40. Multiple Bonds • In some cases, a multiple bond may be needed to satisfy the octet rule. • Ex) N2

  41. Making a Lewis Structure • In general, a Lewis Structure can be set up as follows. • Determine the total number of valence electrons from all atoms in the formula. • Set up a skeleton structure by putting the first element in formula in the middle. Place all the others around this central atom.

  42. Making a Lewis Structure • Draw a bond from the central atom to each external atom, then fill in the external atoms until each has an octet. • Count up all electrons and compare to the total in step #1. • If all are used, go to step #5. • If some are left, then place on central atom as lone pairs to complete its octet.

  43. Making a Lewis Structure • Check the central atom for an octet. • If yes, then you are finished. • If no, then you need to have some multiple bonds. • Do Lewis Structures for: • CF4, NCl3, SBr2, H2O, and CO2

  44. Naming Covalent Compounds • Covalent compounds use prefixes to indicate the number of atoms of each type. • one = mono (used only for second element!) • two = di • three = tri • four = tetra • five = penta • six = hexa

  45. Naming Covalent Compounds • Name the first element in the formula – add the appropriate prefix if there is more than one. • Name the second element in the formula – change the suffix to –ide – include a prefix to indicate the subscript even if it is “1”.

  46. Learning Check • Name: • CO2 • NO • NCl3 • PCl5

  47. Writing a Covalent Formula • Since electrons are shared, charges do NOT apply. • Simply look at the prefixes and apply them. • Ex) sulfur trioxide = • Ex) dinitrogen tetroxide =

  48. The “Big” Picture • A compound is IONIC if: • The first element in the formula or name is a metal or the NH4+1 ion. • A compound is COVALENT if: • The first element in the formula or name is a non-metal or metalloid.

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