Review of Selected Material from Gen Chem I Part I: Bonding & Polarity (mostly from Chapters 8, 9 & 10 of Jespersen 6th ed) Dr. C. Yau Fall 2013

Quick Review: Use of the Periodic Table Size increases going down a column Size increases going from right to left Summary

Quick Review: Use of the Periodic Table What is meant by "first ionization energy?“ It is the energy need to pull one electron away from a neutral gaseous atom. e.g. Mg (g) + energy → Mg+ (g) + e- IE = +737 kJ/mol What does the sign of IE tell you? E has to be added to pull the electron off. How is IE related to the size of the atom? Would a large atom have a high or low 1st ionization energy? Why? Electrons of the larger atom are further from the nucleus and there easier to pull off (lower 1st IE).

Quick Review: Use of the Periodic Table What is the 1st ionization energy trend in the Periodic Table? The general trend is opposite to the trend in size: IE increases as we go UP a column. IE increases as we go from L to R. This is summarized by a diagonal arrow going from lower left to upper right. See next slide.

Highest IE Lowest IE

Smaller atoms should have higher ionization energy Electron is closer to the nuclear charge, thus held more tightly, harder to remove Electron is further from nuclear charge and also nuclear charge is shielded by more layers of innershell electrons. + e- + e-

Quick Review: Use of the Periodic Table What is meant by "electron affinity“ (EA)? It is the energy released when an electron is added to a neutral gaseous atom. e.g. F (g) + e- → F - (g) + 328 kJ The electron affinity of fluorine is – 328 kJ/mol. What does the negative sign tell us? It means E is released. The system is LOSING this amt of E. Element that “likes” electrons has a larger magnitude of EA (more negative EA).

Quick Review: Use of the Periodic Table What is meant by "electronegativity?" It is the ability of an atom in a covalent bond to pull the bonding electrons towards itself. How is it different from electron affinity? The e- is not totally pulled off. They are still being shared by the other atom in the bond.

Quick Review: Use of the Periodic Table How is it similar to electron affinity? It follows the same trend. The more electronegative element would generally have the higher electron affinity (more negative EA). What is the periodic trend for electronegativity? It increases as we move closer to the top right corner of the periodic table.

Electronegativity Trend KNOW WELL! 1. Electronegativity increases going up any column and going from left to right #1 F #2 O #3 (N and Cl) (Memorize this!) Nonmetals are more electronegative than metals. Electroneg. of H is near the metal/nonmetal border. It is more electroneg. than metals but less electroneg. than nonmetals. C has almost the same electroneg. as H.

What does the bold line tell us? Why do we need to know that? It separates metals from nonmetals.

Complete the following comparison: metal + nonmetal nonmetal + nonmetal metal + metal Ionic compound made of cations & anions. Molecule with covalent bonds Alloy (not a compound, just a homogeneous mixture How are alloys different from metalloids? Metalloids are elements along the bold line between metals and nonmetals.

Compare metals to nonmetals for the following attributes: 1st ionization energy Nonmetals > metals Magnitude of electron affinity Electronegativity

Quick Review: Use of the Periodic Table 11 Na 22.990 What information does this give you about Na? 11 protons 11 electrons if neutral How many neutrons?? 1 mole of Na weighs 22.990 grams. 1 atom of Na weighs…? 22.990 u

Use of the Periodic Table Quick Review Use of the Periodic Table 11 Na 22.990 Where are the 11 electrons? octet 1s2 2s2 2p6 3s1 Na+ Which electrons are we most interested in? Why? What would it like to do? It is likely to leave so that Na ends up with an octet. 3s1 only, because it is in the outershell. 15

Use of the Periodic Table Quick Review Use of the Periodic Table What information does this give you about Br? 35 Br 79.904 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5 It has 35 protons, 35 electrons, 79.904 amu per atom, 79.904 g per mole of atoms Which electrons are we most interested in? Why? What would Br like to do? 4s2 4p5 These are the valence electrons. Br would like to gain 1 e- to attain an octet.

Quick Review: Use of the Periodic Table What are valence electrons? How can we tell quickly how many valence electrons an element has? Why do we need to know this number? What are we going to do with it? They are electrons that are most likely to react, for A families, they are in the outershell. The number of valence electrons can be obtained by looking at the Group number in the periodic table. We need to know the number of valence electrons partly in order to write Lewis structures. 17

Quick Review: Chemical Bonding What happens when sodium atoms are mixed with bromine atoms? to form the ionic compound, sodium bromide. 18

Quick Review: Chemical Bonding What happens when chlorine atoms and mixed with bromine atoms? to form the molecular compound bromine chloride.

Quick Review: Chemical Bonding How is a Cl-Cl bond different from a Cl-Br bond? The Cl-Cl bond is nonpolar. The 2 electrons being shared are equally shared. The Cl-Br bond is polar because Cl is more electronegative than Br and the 2 electrons being shared are spend more time closer to Cl than to Br.

Quick Review: Polarity How is bond polarity different from molecular polarity? Bond polarity refers to one bond whereas molecular polarity refers to the entire molecule. Can you have a polar bond but a nonpolar molecule? Such is the case when the symmetry of the molecule allows the bond dipoles to cancel out. Can you have nonpolar bonds but a polar molecule? Yes No

Quick Review: Polarity Draw the Lewis structure of carbon dioxide. Is it polar? Draw the Lewis structure of sulfur dioxide. Draw the Lewis structures of (a) carbonic acid (b) phosphoric acid (c) chlorate ion. (Include non-zero formal charges on all atoms.) Give their geometries (including bond angles). State whether they are polar or nonpolar.