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Chapter 4

Learn about the octet rule and how ions are formed in ionic compounds. Understand the naming and writing of ionic formulas, as well as the concept of polyatomic ions. Explore the different types of compounds, including covalent compounds, electronegativity, bond polarity, and the shapes and polarity of molecules.

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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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