UNIT 7 DAY 1. Ionic Bonding Basics; Dot diagrams

Transcription

1 UNIT 7 DAY 1 Ionic Bonding Basics; Dot diagrams

2 U7D1: Ionic Bonding Basics HW: See Schedule; Lab Due Thursday Do Now: 1.Write your name, date and period on all packets. 2.Look through schedule 3. answer on the back of your schedule: How many electrons do most elements want in the valence shell? How can we determine if an atom will gain lose or share electrons? 11/25 U6 Test 82 12/2 U7 Notes Packet 83 12/2 U7 HW packet 84

3 Agenda 1. Any questions about Unit 6 test? 2. What is bonding? 3. Why bond? 4. Ion formation 5. Ion Lewis Structures 6. What have we learned??

4 Electronegativity (EN): Can help to determine how valence electrons behave in the presence of other valence electrons. Electronegativity is Attraction for electrons in a bond. Elements with the highest EN value: Nonmetals Ex. Elements with the lowest EN value: metals ex Fluorine Francium

5 the ElectroNegativity Difference (END) We can use the (END) to predict the type of bond, which forms between two atoms. The END is just the difference between the two bonding atoms electronegativity (use the absolute or positive value.) a) Use the periodic table to determine type of element (metal or nonmetal) b) look up the Electronegativity of the element (use the chart that you created of ref table S)

6 Element Type EN Value Li Metal 1.0 N Nonmetal 3.0 Example: the END between Li and N:

7 Element EN Element EN END Li Metal Na K O N C O Nonmetal F N H N Cl

8 What is the pattern? When an END is a LARGE difference: IONIC bond formed It s formed between a and metal a. nonmetal The electrons are stolen/transferred from the metal by the nonmetal and a (8 valence electrons). Stable octet When the END is a SMALL difference: Covalent bond forms These type of compounds are called molecules The bonds are formed between nonmetal and nonmetal Neither can steal away the electrons so the nonmetals share electrons to get an octet (or a duet in the case of H). Two types of sharing: Equally = bonding Nonpolar covalent Unequally: bonding polar covalent

9 END (ElectroNegativity Difference) Number Line We can use a END (ElectroNegativity Difference) Number Line to determine the type of bond formed. Draw this number line below the periodic table on your reference tables. Nonpolar covalent Polar covalent Ionic NM + NM NM + NM M + NM

10 I. What is bonding? Types of Bonding: Atomic Glue! The simultaneous attraction by two nuclei for electrons COVALENT BONDING- between 2 nonmetals or metalloid, ex. H 2 O Electrons shared: IONIC BONDING- between a metal and nonmetal,ex. NaCl Electrons transferred:

11 More about that next unit let s talk about Ionic Bonding! Ionic Bonding Basics & Formulas The how and why of Ionic Bonding!

12 II: Ions POSITIVE IONS: formed by metals losing electrons (oxidation) cation +ion called: # electrons lost = Charge on the ion

13 Negative ions Formed when nonmetals gain electrons (reduction) -ion anion called: charge on ion # electrons gained =

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15 III. Why do atoms form bonds? Let s look at electron configuration again. For IONS: When a positive (+) ion forms, cross out the valence electrons of the atom s configuration to get the new ion electron configuration. Atom Electron Configuration # of Valence electrons It s Ion Ion Electron Configuration # of e-1 now in outermost PEL Na Na

16 Negative ions: When a negative (-) ion forms, add the number of electrons equal to the ion charge to the valence shell of the atom s configuration to get the new ion electron configuration.

17 Complete the chart below Mg Ca +2 F -1 Cl Which shows up in the last column of the chart above? In which group on the periodic table do all but one member have this magical number of valence electrons?

18 Group 18 the Noble Gases These elements are very stable and non-reactive. They do not form compounds easily. Having this number of valance electrons is very stable. Atoms form bonds so that they can have this number of valence electrons and mimic the electron configuration of the noble gases. This is called the Stable octet

19 What Noble Gas does each of elements mimic when it forms an ion? Na has 11 e- s (2-8-1), Na +1 has 10 e- s (11e- s 1e- = 10 e- s) when Na forms Na +1, its electron configuration becomes (2-8) the same as Ne (atomic # 10) S has 16 electrons (2-8-6), S -2 has 18 e- s (16e- s +2e- s = 18 e- s) when S forms S -2, its electron configuration becomes (2-8-8) The same as Ar (atomic # 18)

20 You try Atom Atom s # of electrons Ion Mg Mg +2 Ca Ca +2 F F -1 Cl Cl -1 Ion s # of electrons When metals form ions, the electron configuration looks like the noble gas. When nonmetals form ions, the electron configuration looks like the noble gas at end of its row. We have not touched the nucleus, Ion s EC looks like Ne Ar Ne Ar previous so the ions are still the same element that they were, but with different properties than their neutral atom!!

21 IV. Dot Diagrams of Ions: Metals lose their valence electrons A Dot Diagram of a metal ion is the [Ca] +2 ion s symbol & Its charge ONLY- no dots: Nonmetals gain electrons to have 8 valence electrons, A Dot Diagram of a nonmetal ion.. [ :F:.. ] -1 is the symbol with 8 DOTS and its charge:

22 You know what you need to do

23 V. IONIC BONDING BASICS When metals and nonmetals react together, the metal gives away its valence electron(s) to the nonmetal forming positive ions whose positive charge is equal to the number of valence electrons lost. The nonmetal gains the electrons and becomes a negative ion whose negative charge is equal to the number of valence electrons it has gained. The positive ion, cation, and the negative ion, anion, attract to each other forming a new compound. (opposite charges attract)

24 The three steps in forming an ionic bond are: Metal loses e- to nonmetal becoming a cation. 1. Nonmetal gains e- from metal to become an anion. 2. Cation and anion attract to form an ionic compound. 3.

25 Let s practice

26 More???? Neutral Metal s Dot Diagram Neutral Nonmetal s Dot Diagram Transfer of electrons from Metal to Nonmetal Resulting Dot Diagram Formula Al Cl So.. Fist to Five Fist (not understanding need help) Five (feel I can teach it) Show me where you stand

27 Ionic Formula Writing The number of each type of ion that will form the new compound will depend on the size or magnitude of the charges (oxidation states). The charges must add up to zero. Ex. sodium reacts with chlorine, sodium forms a Na +1 ion & chlorine forms a Cl -1 ion. Only one of each ion is necessary -> the charges add up to zero: (+1) + (-1) =0 the formula of the new compound, sodium chloride, is simply NaCl.

28 but what if the charges aren t equal and opposite? If sodium reacts with oxygen, sodium still forms a Na +1 ion but oxygen forms a O -2 ion. The new compound, sodium oxide, will require 2 Na +1 for every O -2 : 2(+1) + (-2) =0. The formula for sodium oxide is Na 2 O.

29 Remember: the charges are written as superscripts (Na +1 ) and the counters in formulas are written as subscripts (Na 2 O). Positive ions are written first and negative ions are written second in a formula. Lazy chemists do not bother to write 1 as counter in a formula. The element's symbol stands for the 1. Ionic formulas are always written in lowest terms. => an empirical formula. NaCl and Na 2 O are binary (2 element) ionic cds.

30 VI. DETERMINING CHARGES: The oxidation state or number is the charge or apparent charge an atom has in a compound. To determine the charge, simply look at the Periodic Table in the upper right corner for the oxidation states of the element. For nonmetals it is the FIRST (top) oxidation state ONLY. For many metals, there is only one possibility for the charge. Transition metals and those metals close to the crack, there are more than one charge.

31 Look up the charges on the following: Remember to write the charges as superscript Sr Ag Cl N Cs O Fe Fe Cu Cu P Br

32 WRITING BINARY FORMULAS The ions of the elements combine in such a way that the charges have to add up to zero. Metal or positive ion (cation) is written FIRST Nonmetal or negative ion(anion)is written SECOND. The number one,1, is not written in the formula ex. NaCl.

33 Only the number in the charge for each ion is crisscrossed down and turned into subscripts. Always check that the formula is in LOWEST terms. K +1 O -2 K O K 2 O 1 or K 2 O Pb +4 O -2 -> Pb O -> Pb 2 O 4 simplifies to PbO 2

34 So Let s look at the different combinations we can have Ions to be Bonded X +1 & Y -1 X +2 & Y -2 X +3 & Y -3 X +2 & Y -1 X +3 & Y -1 How to determine formula Cation Anion +1 and -1 add up to zero already +2 and -2 add up to zero already +3 and -3 add up to zero already It takes two -1 charges to cancel out the +2 charge It takes three -1 charges to cancel out the +3 charge Formula

35 Ions to be Bonded X +1 & Y -2 X +1 & Y -3 X +2 & Y -3 X +3 & Y -2 X +4 & Y -2 How to determine formula Cation Anion It takes two +1 charges to cancel out the -2 charge It takes three +1 charges to cancel out the -3 charge Common denominator: 2x3=6 it takes three +2 to make +6 and two - 3 to make -6 Common denominator: 2x3=6 it takes two +3 to make +6 and three - 2 to make -6 It takes two -2 charges to cancel out the +4 charge Formula

36 What have you learned? Periodic Tables out! 1. How many electrons do most atoms want in the outer shell? 2. The ion electron configurations of all atoms will match the nearest 3. What is the electron configuration for Li Metals form ions by electrons. 5. Draw the ion dot diagram for Aluminum. 6. Draw the ion dot diagram for CaO 7. How prepared did you feel for this check?