Name: Period: Date: UNIT 12: Solutions Lesson 2: Electronegativity and Polarity!

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1 Name: Period: Date: UNIT 12: Solutions Lesson 2: Electronegativity and Polarity! By the end of today, you will have an answer to: What is electronegativity and how does it lead to molecules being polar or not polar? Do Now: (1) A student mixes sand in water and says that he has just made a solution. Explain why this student is incorrect. (2) When you make Kool Aid, what is the solute and what is the solvent? (3) Of the two substances above (sand and Kool-Aid), which is soluble in water and which is insoluble? Oil & Water Oil and water DO NOT mix because water is and oil is. What makes some molecules polar and others nonpolar? Electronegativity The ability of an atom to attract electrons when in a compound. When atoms bond, if there is a large electronegativity difference the electrons spend more of their time near one atom than the other atom. Consider H 2O Using Table S Picture What is the electronegativity of H? What is the electronegativity of O? Which of the two atoms is more attracted to the electrons? Water is Polar (a) What does it mean for water to be polar? Oxygen gas, which is (O 2) Picture What is the electronegativity of O? What is the electronegativity of O? Which of the two atoms is more attracted to the electrons?

2 Try these 1) Identify the bonds between atoms of each pair of elements as nonpolar covalent, polar covalent, or ionic. a) H and Br b) O and O c) Na and Cl d) Br and Br e) H and I f) NF 3 2) The chemical bond between which two atoms is most polar? (HINT: The bigger the difference in electronegativity, the more polar) (1) C N (3) S Cl (2) H H (4) Si O EXCEPTIONS Symmetrical molecules are nonpolar because no atom wins the tug of war! Nonpolar Molecule Picture CF 4 and CCl 4 CO 2 Summary For a molecule to be polar it needs: 1) In terms of charge distribution For a molecule to be non-polar it needs: 1) In terms of charge distribution 2) In terms of electronegativity 2) In terms of electronegativity

3 Name: Pd: Date: CW 12.2 Electronegativity and Polarity 10 points (1) Explain, in your own words, what is electronegativity? Where do you find it on the reference tables? (2) Explain, in terms of charge distribution and electronegativity, why water is polar? (3) Answer the questions in the chart below. CF 4 H 2O Why is it nonpolar, in-terms of charge distribution? Why is it polar, in-terms of charge distribution? Br 2 NF 3 Why is it nonpolar, in-terms of electronegativity difference? Why is it polar, in-terms of electronegativity difference? (4) Which formula represents a nonpolar molecule? (1) HCl (3) NH 3 (2) H 2O (4) CH 4 (5) Which atom has the weakest attraction for electrons in a bond with an H atom? (1) Cl atom (3) O atom (2) F atom (4) S atom (6) An atom of which element has the greatest attraction for electrons in a chemical bond? (1) As (3) Ge (2) Ga (4) Se

4 (7) Which formula represents a polar molecule? (1) H 2 (3) CO 2 (2) H 2O (4) CCl 4 (8) The chemical bond between which two atoms is most polar? (1) C N (3) S Cl (2) H H (4) Si O (9) Which term indicates how strongly an atom attracts the electrons in a chemical bond? (1) Alkalinity (3) electronegativity (2) Atomic mass (4) activation energy (10) Which molecule contains a nonpolar covalent bond? (11) Why is a molecule of CO 2 nonpolar even though the bonds between the carbon atom and the oxygen atoms are polar? (1) The shape of the CO 2 molecule is symmetrical. (2) The shape of the CO 2 molecule is asymmetrical. (3) The CO 2 molecule has a deficiency of electrons (4) The CO 2 molecule has an excess of electrons. (12) Explain, in terms of electronegativity, why a P-Cl bond is a molecule of PCl 5 is more polar than a P-S bond in a molecule of P 2S 5. (13) Explain, in terms of charge distribution, why a molecule of hydrogen cyanide is polar. (14) Explain, in terms of electronegativity difference, why the bond in a molecule of HF is more polar than the bond in a molecule of HI. [1]

5 Work hard. Be nice. Name: Pd: Date: HW 12.2 Electronegativity and Polarity 10 points 1) The atoms of which element in Group 16 (VIA) of the Periodic Table have the greatest tendency to gain electrons? (1) O (2) Se (3) S (4) Te 2) Based on Reference Table S, atoms of which of these elements have the strongest attraction for the electrons in a chemical bond? (1) Al (2) P (3) Si (4) S 3) Which element has an atom with the greatest attraction for electrons in a chemical bond? (1) As (2) N (3) Bi (4) P 4) As the elements of Group 17 are considered in order of increasing atomic number, there is an increase in (1) atomic radius (2) electronegativity (3) first ionization energy (4) number of electrons in the first shell 5) An atom of which element has the greatest attraction for the electrons in a bond with a hydrogen atom? (1) chlorine (2) silicon (3) phosphorus (4) sulfur 6) Which halogen has the least attraction for electrons? (1) F (2) Br (3) Cl (4) I Name: Pd: Date: HW 12.2 Electronegativity and Polarity 10 points 1) The atoms of which element in Group 16 (VIA) of the Periodic Table have the greatest tendency to gain electrons? (1) O (2) Se (3) S (4) Te 4) As the elements of Group 17 are considered in order of increasing atomic number, there is an increase in (1) atomic radius (2) electronegativity (3) first ionization energy (4) number of electrons in the first shell 2) Based on Reference Table S, atoms of which of these elements have the strongest attraction for the electrons in a chemical bond? (1) Al (2) P (3) Si (4) S 3) Which element has an atom with the greatest attraction for electrons in a chemical bond? (1) As (2) N (3) Bi (4) P 5) An atom of which element has the greatest attraction for the electrons in a bond with a hydrogen atom? (1) chlorine (2) silicon (3) phosphorus (4) sulfur 6) Which halogen has the least attraction for electrons? (1) F (2) Br (3) Cl (4) I

6 Work hard. Be nice. 7. Is the bond between N and H polar or non-polar? [1] 8. Which atom in a C F bond would be slightly negative? [1] 9. Explain, in terms of electronegativity difference, why the bond between hydrogen and oxygen in a water molecule is more polar than the bond between hydrogen and nitrogen in an ammonia molecule. [1] 10) The chemical bond between which two atoms is most polar? (1) C N (2) H H (3) S Cl (4) Si O 11) Which structural formula represents a nonpolar molecule? a. b. c. d. 7. Is the bond between N and H polar or non-polar? [1] 8. Which atom in a C F bond would be slightly negative? [1] 9. Explain, in terms of electronegativity difference, why the bond between hydrogen and oxygen in a water molecule is more polar than the bond between hydrogen and nitrogen in an ammonia molecule. [1] 10) The chemical bond between which two atoms is most polar? (5) C N (6) H H (7) S Cl (8) Si O 11) Which structural formula represents a nonpolar molecule? a. b. e. f.