2. October 15 th 2009 Objectives  SWBAT Identify oxidation numbers for given ions  SWBAT State the definition of electronegativity  SWBAT explain electronegativity trends on the periodic table Catalyst  Write down the stable ion that will form for the following elements: Be able to explain why…  Na, Ar, O, Mg  Label the ions above as cations or anions

3. Catalyst Review  Na +1, because sodium needs to lose 1e- to be stable  Ar, because Argon is already stable, it does not lose or gain any e-.  O 2-, because Oxygen needs to gain 2e- to be happy  Mg 2+, because magnesium needs to lose two electrons to be happy

4. Agenda  Catalyst Review (15min)  Welcome to Unit 4 (5min)  Compounds and Chemical Bonds (10min)  Oxidation numbers (5min)  Electronegativity (20min)  Practice (25min)  Exit Ticket (10min)

5. New word  Oxidation Number – the positive or negative charge on an ion  What is the oxidation number of Sodium?  Argon?  Na +1  Ar  O 2-  Mg 2+

6. What to expect in Unit 4  You will learn about…  Compounds (ionic and covalent)  Chemical formulas  Electronegativity, ionization energy, polarity  Naming compounds  Valence electrons continued  Lewis structures  You will get to…  Make Ionic Personal Ads!  Speed Date!

7. Atom - the smallest particle of an element

8. What is a compound?  A compound is a pure substance  A compound is a combination of two or more different elements that are chemically combined Water molecules Add to Vocabulary Log!

9. Familiar Compounds and Their Formulas  Vinegar  Acetic acid  CH 2 COOH

10. Grain Alcohol  Ethanol  C 2 H 5 OH

11. Cane sugar  Sucrose  C 12 H 22 O 11

12. Stomach acid  Hydrochloric acid  HCl

13. What is a compound?  A compound is a pure substance  A compound is a combination of two or more different elements that are chemically combined Remember! Electrons do all the work in chemical bonds! Atoms do 3 things with electrons: 1.Give them away 2.Take them 3.Share them

14. What is a chemical bond?  A chemical bond is the force that holds two atoms together in a compound (attractive force)  There are two main types of bonds:  Ionic  Covalent

15. Chemical Bond Spotlight: NaCl (table salt) 2 different elements:  Sodium (Na)  Chlorine (Cl) 1 compound:  Sodium chloride (NaCl) NaCl NaCl

16. Chemical Bond Spotlight: NaCl (table salt)

17. Chemical Formula  A chemical formula is a combination of chemical symbols used to represent a compound.  A chemical formula contains the number of each atom in the compound.

18. Ratio Examples  KBr has 1 atom of K and 1 atom of Br  H 2 O has 2 atoms of H and 1 atom of O  CO 2 has 1 atom of C and two atoms of O

19. Subscript Numbers  Subscript numbers are small numbers placed to the lower right of element symbols and are used to show how many atoms of each element are present H2OH2OCO 2

20. Chemical Formulas  What is a chemical formula?  What is a subscript number?  What does the subscript number tell us? If there is no number, it is an implied ONE  Example: Na 2 CO 3  2 atoms Na (sodium)  1 atom C (carbon)  3 atoms O (oxygen)  6 total atoms (2 + 1 + 3 = 6) RATIO 2 Na : 1 C : 3 O

21. Chemical Formula Practice  Determine the number of each atom in the following compounds. 1. N 2 2. CO 3. H 2 CO 3 4. KOH 5. CaCO 3 6. KNO 3

22. What is electronegativity?  Electronegativity is…  The ability of an atom to attract electrons to itself in a chemical bond  How much an atom wants electrons  Electronegativity is expressed in numerical values of 4.0 or less  These numerical values are called Paulings  Higher number means the atom will attract electrons in a chemical bond

23.  Rb has an electronegativity value of.82 Paulings  Br has an electronegativity value of 2.96 Paulings  Which one wants an electron more?

24. Graphing Electronegativity  On two white boards in your groups:  Draw a line graph  X-axis: Element  Y-axis: Electronegativity  Part 1 – points = dots  Part 2 – points = squares

25. Elements and their Electronegativity (1) (Logistics manager copy down the chart for your group) ElementElectronegativity (Paulings) Hydrogen2.20 Lithium0.98 Sodium0.93 Potassium0.82 Rubidium0.82 Cesium0.79 Francium0.70

26. Elements and their Electronegativity (2) ElementElectronegativity (Paulings) Lithium0.98 Beryllium1.57 Boron2.04 Carbon2.55 Nitrogen3.04 Oxygen3.44 Fluorine3.98

27. What trend(s) do you notice?

28. Electronegativity Electronegativity decreases as you go down the periodic table and increases as you go left to right across the periodic table.

29. Practice Problems  Rank the following elements in order of increasing electronegativity based on location on the periodic table (smallest to biggest) Mg, Sr, Be, Ra Cl, Si, Al, S, P Radon, Strontium, Magnesium, Beryllium Aluminum, Silicon, Phosphorus, Sulfur, Chlorine

30. Let’s Think about the Trends…  Discuss the following question with your group…10 class points if you come up with the right answer.  Why do Alkali metals have such low Electronegativities and Fluorine such a high electronegativity?  Why aren’t electronegativities listed for the Noble gases?

31. The Answer…  Electronegativity tells us how much an atom wants to TAKE an electron. (- charge)  The alkali metals have low electronegativities because in order to be stable (happy) they need to GET RID of an electron. (+ charge)  Halogens have a high electronegativity because in order to be stable (happy) they need to GAIN an electron (- charge)  Noble gases are already happy, so they do not want to gain or lose an electron (EN of zero)

32. How does atomic size related to electronegativity? Atomic size is indirectly related to electronegativity ELECTRONEGATIVITY ATOMIC SIZE As electronegativity increases, atomic size decreases!

33. Why is this relationship true?  Atoms with HIGH ELECTRONEGATIVITIES hold their electrons very close!  Sooooo, the atomic size decreases High or low electronegativity? Large or small atomic size?

34. Practice Time! (15min) 1. T or F? Electronegativity decreases as you move left across the periodic table. 2. T or F? As you move down the Periodic Table, atoms get more electronegative. 3. Rank the following sets of elements in order of increasing electronegativity (small  big). Set A: Bh, Mn, Re, TcSet B: Sb, I, Ag, Ru Set C: Y, Ti, Sg, Ta 4. Rank the following sets of elements in order of decreasing electronegativity (big  small). Set A: Cl, At, I, F, BrSet B: Te, Xe, Sn, In Set C: Rb, K, Sr, Ca 5. Why do Alkali metals have a lower EN then Halogens? 6. Why don’t the Noble Gases have an EN? 7. What is the relationship of atomic size to electronegativity? 8. Why does this relationship exist? 9. What are the oxidation numbers for the following elements? A. Fluorine, Barium, Francium, Helium, Arsenic