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UNIT 5: Chemical Bonding (overview) & Ionic Compounds

UNIT 5: Chemical Bonding (overview) & Ionic Compounds. Chem I/IH: Chapter 7. Unit 5: Chemical Bonding & Ionic Compounds ESSENTIAL QUESTIONS.

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UNIT 5: Chemical Bonding (overview) & Ionic Compounds

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  1. UNIT 5: Chemical Bonding (overview)& Ionic Compounds Chem I/IH: Chapter 7

  2. Unit 5: Chemical Bonding & Ionic CompoundsESSENTIAL QUESTIONS EQ #1: What are the properties and differences between ionic and covalent bonding, including predicting bonding polarity based on electronegativity differences. EQ # 2: What is the electron sea-model of metallic bonding and relate it to the properties of metals? EQ# 3: How can I determine the formula for a binary and tertiary ionic compounds? EQ# 4: How can I name ionic compounds when given the chemical formula?

  3. Lewis Dot Diagram • Definition: System of showing the valence e-s for an atom • Help us predict bonds

  4. Lewis Dot Diagram, cont. 1) Element symbol in middle 2) Valence e-s represented by dots • Place v.e.-s around the element symbol in 4 locations • Above • Below • Left • Right • Don’t pair up any, until 1 in each location. LEAVE ROOM FOR SOME PRACTICE PROBLEMS (1/2 PAGE)

  5. Predicting valence electrons in main group elements • The group number helps you identify the number of valence e-s. (Label your P. Table!)

  6. The Chemical Bond (definition) • The force that holds two atoms together • Occurs using valence (outermost) electrons

  7. The Noble Gases • All occur in nature because they are stable • BUT no compounds containing them are ever found in nature. They have no desire to form bonds. • Common denominator is that they all have 8 valence e-s, called an OCTET. (*except He, which has 2) • This is what makes them stable/unreactive • This is called “Noble Gas Configuration” (NGC)

  8. All “Other” Elements • have less than the ideal 8 valence electrons (or 2 valence electrons for VERY small atoms) • “want” NGC, so they can be stable.

  9. Two ways atoms can Get NGC 1. Lose/gain e-s (IONIC bond) • This occurs when the 2 atoms in the bond pull on their e-s w/different strengths • Typically occurs btwn a METAL & a NONMETAL.

  10. Two ways atoms can Get NGC 2. Share e-s (COVALENT bond) • This occurs when the 2 atoms in the bond pull on their e-s w/the same (or similar) strength • Typically occurs between 2 NONMETALS. • 2 minute video w/types of bonding

  11. NOTE (don’t copy, but READ!) • 2 metals will NOT form a new compound. Instead, they form an ALLOY, as discussed in our unit on Matter.

  12. 3 “Classes” of Elements(Don’t Copy) • Metals =pink Conductors? Yes! Hold e-s? Loosely How many V.E’s? 1-3 • Nonmetals =green Conductors? No! Hold e-s? Tightly How many V.E.’s? 5-7 • Metalloids =blue “In between”

  13. Ions & the Octet Rule • Ions are charged particles that have lost or gained e-s to satisfy the octet rule (8 valence e-s) • They will typically form in the way that requires the smallest gain or loss of e-s to complete an octet. • Ex: Na  Na+ + e- • Ex: Cl + e-  Cl- “cation” “anion”

  14. Ions & the Octet Rule, cont. • This also means that atoms will typically obtain the NGC of the nearest *noble gas • *“Nearest” means the one with the closest atomic number • Ex: Na (Z=11) obtains the NGC of Neon (Z=10), not Argon (Z=18) Z = 10 11 12 13 14 15 16 17 18 19 • Ne Na Ar • X

  15. Formation of Ions • The charge on an ion is called its “oxidation number”

  16. Formation & Naming of Ions, cont. • Metals tend to lose electrons • Have + oxidation # • Called “cations” • Metal ions are given the element name • Ex: Na+ = “sodium ion”

  17. Formation & Naming of Ions, cont. • Nonmetals tend to gain electrons • Have – oxidation # • Called “anions” • Nonmetal ions are given the element name w/an “-ide” ending • Ex: O2- = “oxide ion”

  18. How to Identify the Charge on an Ion Step 1: Decide which noble gas your element is closest to. (This is the electron whose e- configuration your atom will become like.) Ex: Aluminum • Ne = 10 e-s • Al = 13 e-s • Ar = 18 3-s Step 2: Mathematically find the charge on the ion. Protons = 13+ Electrons = 10- Overall charge= 3+ lose 3 e-s gain 5 e-s

  19. PracticeWhat is the charge on a magnesium ion? Step 1: Is it easier for magnesium to lose or gain electrons? Step 2: Mathematically find the charge on the ion. • Protons = 12+ • Electrons = 10- • OVERALL CHARGE = 2+ HINT: Magnesium is a metal with 2 valence e-s. Answer: Mg will lose 2 e-s.

  20. PracticeWhat is the charge on a nitrogen ion? Step 1: Is it easier for nitrogen to lose or gain electrons? Step 2: Mathematically find the charge on the ion. • Protons = 7+ • Electrons = 10- • OVERALL CHARGE = 3- HINT: Nitrogen is a nonmetal with 5 valence e-s. Answer: N will gain 3 e-s.

  21. e- Configuration of ions • We can write electron configurations for ions, similar to how we write them for atoms. • Ex: on the previous slide, we said nitrogen gained 3 electrons.

  22. Formation of an ionic bond • When e-s are lost by 1 atom they are gained by another. • Therefore, cations & anions are formed at the same time! • Ex: Na & Cl

  23. Formation of an ionic bond, cont. POSITIVE ION NEGATIVE ION Now opposite charges attract! The attraction between + and - ions is what forms the bond. Positive ions and negative ions form a lattice Every positive ion is surrounded by negative ions and every negative ion is surrounded by positive ions

  24. Practice (don’t copy, but leave space in your notes for these examples) 1. Draw Lewis Dot Diagrams for sodium and chlorine ATOMS. 2. Show how e-s rearrange to form sodium & chlorine IONS. 3. Write the formula (cation, then anion) 4. Name this compound (cation, then anion) 5. (BONUS: What NG is each ion like?)

  25. Writing Ionic Compound Formulas Example: Aluminum Chloride Step 1: Al 3+ Write the cation with charge Step 2: Al Cl 3+ 1- Write anion with charge Al Cl Step 3: 1 3 “Drop & swap” charges as subscripts AlCl3 Step 4: Make sure subscripts are lowest ratio (“1” is never shown) 1 Al: 3 Cl 1:3 is lowest ratio

  26. Practice Together • Write the formula for calcium oxide. • Write the formula for magnesium fluoride • Write the formula for aluminum sulfide

  27. Formation of an ionic bond, cont. (don’t write) • Note: you will not always have a 1:1 ratio of + to - ions. • Ex: MgI2 -see next slide

  28. Formation of MgI2 (don’t write) .. .. • .Mg. + :I: → Mg.+ + :I: - (are they happy?) . .. .. .. .. .. • .Mg. + :I: :I: → Mg2+ + :I: - :I:- . . .. ..

  29. What Formulas Tell Us • …the elements that make up the compound • …the # of atoms of each element in a unit of the compound • The smallest unit of an Ionic Compound is called a “Formula Unit” ex: MgCl2 • The smallest unit of a Covalent compound is called a Formula Unit or “Molecule” ex: CH4

  30. Using Oxidation #s to Write Formulas for Ionic Compounds(Read but don’t copy) A compound has NO CHARGE on it, so a formula must have equal numbers of + & - charges. (use the LCM) LecturePLUS Timberlake

  31. Polyatomic Ions • (Def): Charged particles containing more than one element! • Ex: SO 32- = “sulfite” • Copy the table from p 257 of text (ChemIH) onto YOUR P TABLE

  32. Writing Ionic Compound with POLYATOMIC IONS Example: Aluminum Sulfite Step 1: Al 3+ Write the cation with charge Step 2: Al SO3 3+ 2- Write anion with charge Al (SO3) Step 3: 2 3 “Drop & swap” charges as subscripts Al2(SO3)3 Step 4: Make sure subscripts are lowest ratio (“1” is never shown) 2 Al: 3 SO3 2:3 is lowest ratio SUGGESTION: Put your polyatomics in parentheses every time! We NEVER change subscripts IN polyatomic ions

  33. Writing Formulas for Ionic Compound w/Transition Metals • If you are writing a formula from the name of a compound, follow the usual steps as for a binary ionic compound. (drop & swap, etc.) • The charge on the cation is GIVEN in the name. • Ex: manganese (IV) oxide • Mn 4+ and O 2-

  34. Writing Formulas for Ionic Compounds containing Transition Metals Follow the same steps as for a binary ionic compound. LecturePLUS Timberlake

  35. Naming Ionic Compounds Containing Transition Metals • Identify & name the cation. • Find the charge on the anion. • Find the total negative charge on all the ions. • Divide this total by the number of cations. • This is the charge on the cation. • Include the charge on the cation written as a roman numeral in parentheses. • Identify & name the anion. Ex: FeO FeO

  36. Websites (Don’t Copy) • “Puzzle” formation of ionic & covalent compounds http://www.learner.org/interactives/periodic/groups_interactive.html • Quiz about atomic structure, etc.

  37. Unit 5: Chemical Bonding & Ionic CompoundsSCALES

  38. Unit 5: Chemical Bonding & Ionic CompoundsKEY TERMS • valence electrons • octet • molecule • ionic compound • ion • cation • anion • binary compound • tertiary compound • electronegativity • molecular compound • covalent bond • single bond • double bond • triple bond • multiple bond • bond polarity • sea of electrons • VSEPR theory • polyatomic ion • metallic bond

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