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

Transcription

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

2 Unit Objectives (Copy) To be able to: Explain why some elements react (form bonds.) Explain the difference between an ionic & a covalent bond. Identify the ion formed from a given atom & draw the Lewis Dot Diagram for both atom & ion. Write the proper formula & name for an ionic compound. Write the proper formula & name for a covalent compound.

3 The Chemical Bond (definition) The force that holds two atoms together Occurs using valence electrons

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

5 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.

6 Lewis Dot Diagram, cont. Practice: Together: let s do LDD for Hydrogen, helium, You practice: lithium, beryllium, boron, carbon, nitrogen, oxygen, fluorine, neon.

7 Lewis Dot Diagram of Main Group Elements (copy a few)

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

9 The Noble Gases All occur in nature BUT no compounds containing them are ever found in nature Common denominator is that they all have 8 valence e-s. (*except He, which has 2) This is what makes them stable/unreactive This is called Noble Gas Configuration (NGC)

10 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.

11 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.

12 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

13 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.

14 Metals = pink Conductors? Yes! Hold e-s? Loosely How many V.E s? Classes of Elements (Don t Copy) Nonmetals = green Conductors? No! Hold e-s? Tightly How many V.E. s? 5-7 Metalloids = blue In between

15 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

16 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 = » Ne Na Ar X

17 Formation of Ions The charge on an ion is called its oxidation number

18 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

19 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: O 2- = oxide ion

20 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 lose 3 e-s gain 5 e-s Step 2: Mathematically find the charge on the ion. Protons = 13+ Electrons = 10- Overall charge= 3+

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

22 Practice What is the charge on a nitrogen ion? Step 1: Is it easier for nitrogen to lose or gain electrons? Answer: N will gain 3 e-s. 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.

23 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.

24 TO DO: Label Your Periodic Table Label Groups 1, 2, 13, 15, 16, 17 w/the oxidation number of ea group. Group # Charge

25 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

26 POSITIVE ION Formation of an ionic bond, cont. Now opposite charges attract! NEGATIVE ION 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

27 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?)

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

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

30 Formation of an ionic bond, cont. (don t write) Note: you will not always have a 1:1 ratio of + to - ions. Ex: MgI 2 -see next slide

31 Formation of MgI 2 (don t write).....mg. + :I: Mg. + + :I: - (are they happy?) mg. + :I: :I: Mg 2+ + :I: - :I:

32 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: MgCl 2 The smallest unit of a Covalent compound is called a Formula Unit or Molecule ex: CH 4

33 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 34

34 Using the LCM to Write Ionic Formulas (Practice-don t copy) Ex: Li & F Ex: Li & O Ex: Al & O LecturePLUS Timberlake 35

35 Polyatomic Ions (Def): Charged particles containing more than one element! Ex: SO 3 2- = sulfite Copy the table from p 257 of text (ChemIH) onto YOUR P TABLE

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

37 Transition Metals (Don t Copy!) The d sublevel e-s are so close in energy to the actual (s sublevel) valence e-s, they sometimes act like valence e-s! Transition metals may sometimes have multiple oxidation states Sometimes an atom can lose all its valence e-s. Sometimes an atom can lose all its valence e-s AND some d sublevel e-s. See Table 5.4 on p 164 of OLD RED text: Common Ions of Select Transition Metals Ex: Fe 2+ & Fe 3+ Write the e- configuration LecturePLUS Timberlake 38

38 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-

39 Writing Formulas for Ionic Compounds containing Transition Metals Follow the same steps as for a binary ionic compound. LecturePLUS Timberlake 40

40 Naming Ionic Compounds Containing Transition Metals 1. Identify & name the cation. FeO 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. 2. Identify & name the anion. Ex: FeO

41 Quiz (Don t Copy) 1. Ionic bonds are formed by the of electrons. 2. Covalent bonds are formed by the of electrons. 3. CO is a/n ionic/covalent compound. 4. NaF is a/n ionic/covalent compound.

42 Websites (Don t Copy) Puzzle formation of ionic & covalent compounds groups_interactive.html Quiz about atomic structure, etc.