Chapter 10 Structures of Solids and Liquids

1. Chapter 10 Structures of Solids and Liquids 10.3 Electronegativity and Polarity

2. Electronegativity: Trends Among Groups and Periods of the Periodic Table • http://education-portal.com/academy/lesson/electronegativity-trends-among-groups-and-periods-of-the-periodic-table.html

3. Electronegativity Electronegativity • is the relative ability of atoms to attract shared electrons • is higher for nonmetals, with fluorine as the highest with a value of 4.0 • is lower for metals, with cesium and francium as the lowest with a value of 0.7 • increases from left to right going across a period on the periodic table • decreases going down a group on the periodic table

4. Electronegativity • The most commonly used method of calculation is that originally proposed by Linus Pauling, commonly referred to as the Pauling scale. • Linus Pauling's book, How to Live Longer and Feel Better,advocated very high intake of Vitamin C.

5. Some Electronegativity Values for Group A Elements

6. Electronegativity generally increases from left to right across a period Electronegativity decreases down a group for representative elements Fluorine is the most electronegative element (4.0)

7. Learning Check Using the periodic table, predict the order of increasing electronegativity for the elements O, K, and C.

8. Solution The metal K on the left of Period 4 has the lowest electronegativity of the three elements. The nonmetal O on the upper right of Period 2 has the highest electronegativity. The nonmetal C, which is on the left of O in the periodic table, has a lower electronegativity than O, but a higher electronegativity than K. Order of increasing electronegativity: K, C, O

9. Nonpolar Covalent Bonds A nonpolar covalent bond • occurs between nonmetal atoms • consists of an equal (or almost equal) sharing of electrons • has a zero (or close to zero) electronegativity difference of 0.0 to 0.4 Examples: Atoms Electronegativity Type of Bond Difference NN3.0 - 3.0 = 0.0 Nonpolar covalent ClBr3.0 - 2.8 = 0.2 Nonpolar covalent HSi 2.1 - 1.8 = 0.3 Nonpolar covalent

10. Polar Covalent Bonds A polar covalent bond • occurs between nonmetal atoms • consists of atoms that share electrons unequally • has an electronegativity difference range of 0.5 to 1.7 Examples: Atoms Electronegativity Type of Bond Difference OCl3.5 - 3.0 = 0.5 Polar covalent ClC3.0 - 2.5 = 0.5 Polar covalent OS 3.5 - 2.5 = 1.0 Polar covalent

11. Comparing Nonpolar vs Polar Covalent Bonds

12. Ionic Bonds An ionic bond • occurs between metal and nonmetal ions • is a result of electron transfer • has a large electronegativity difference (1.8 or more) Examples: Atoms Electronegativity Type of Bond Difference ClK3.0 – 0.8 = 2.2 Ionic NNa3.0 – 0.9 = 2.1 Ionic SCs 2.5 – 0.7 = 1.8 Ionic

13. Electronegativity and Bond Types

14. Predicting Bond Types

15. Learning Check Use electronegativity differences to classify each of the following bonds as nonpolar covalent (NP), polar covalent (P), or ionic (I): A bond between A. K and N B. N and O C. Cl and Cl D. H and Cl

16. Solution Atoms in Electronegativity Type of Bond Difference Bond A. K and N 2.2 ionic (I) B. N and O 0.5 polar covalent (P) C. Cl and Cl 0.0 nonpolar covalent (NP) D. H and Cl 0.9 polar covalent (P)

17. Polar Molecules A polar molecule • contains polar bonds • has a separation of positive and negative charge called a dipole indicated by a dipole arrow • has dipoles that do not cancel

18. Nonpolar Molecules A nonpolar molecule • may contain identical atoms (nonpolar bonds) • may have a symmetrical arrangement of polar bonds that cancel dipoles

19. Determining Molecular Polarity The polarity of a molecule is determined from its • electron-dot formula • shape • polarity of the bonds • dipole cancellation

20. Polar or Nonpolar? Which one is polar: CO2 or H2O? H2O CO2

21. Dipole Moment and Polarity

22. Molecular Polarity • Provides information on a substance’s chemical and physical properties • Melting points and boiling points H2O vs. CH4 Bp: 100 oC Bp: -161 oC • Explains solubility of substances • Likes dissolve in likes.

23. Learning Check Identify each of the following molecules as (P) polar or (NP) nonpolar: A. PBr3 B. HBr C. Br2 D. SiBr4

24. Solution Identify each of the following molecules as (P) polar or (NP) nonpolar: A. PBr3 (P) pyramidal; dipoles don’t cancel; polar B. HBr (P) linear; one polar bond (dipole); polar C. Br2 (NP) linear; nonpolar bond; nonpolar D. SiBr4 (NP) tetrahedral; dipoles cancel; nonpolar

25. Halogens are highly reactive, and as such can be harmful or lethal to biological organisms in sufficient quantities. This high reactivity is due to the atoms being highly electronegative due to their high effective nuclear charge. They can gain an electron by reacting with atoms of other elements. Fluorine is one of the most reactive elements in existence, attacking otherwise inert materials such as glass, and forming compounds with the heavier noble gases. It is a corrosive and highly toxic gas. The reactivity of fluorine is such that if used or stored in laboratory glassware, it can react with glass in the presence of small amounts of water to form silicon tetrafluoride (SiF4). Thus fluorine must be handled with substances such as Teflon (which is itself an organofluorine compound), extremely dry glass, or metals such as copper or steel which form a protective layer of fluoride on their surface

26. Nonbonding pairs affect molecular polarity; they pull the electron density strongly.

27. MOLECULAR GEOMETRY AND VSEPR Valence Shell Electron Pair Repulsion • VSEPR is used to predict the molecular geometries of compounds based on the number of electron groups attached to the center atom of the molecule. • Most important factor in determining the geometry is minimizing the relative repulsion between electron pairs. • Molecules’ or ions’ geometry reflects arrangement that favors minimal electron repulsion.