Back ©Bires, 2002 Slide 1 Bires, 2009 Chapter 5: Periodic Trends The investigation and understanding of the atom is what chemistry is all about! Topics rearranged from your text. Over the next week, you should read pages Periodic Law: …

Back ©Bires, 2002 Slide 2 Bires, 2009 The Periodic Table –a collection of all the known elements into a model that groups elements with similar properties. Groups –Vertical columns of elements with similar properties. Periods –Horizontal rows of elements with atomic mass and similar electron configurations.

Back ©Bires, 2002 Slide 3 Bires, 2009 Periodic Table History Dmitri Mendeleev –Russian chemist, ordered the known elements according to properties and masses. (Gaps?) Henry Moseley –arranged the elements according to atomic number (# of protons). –This is the system we use today. Periodic Law –chemical and physical properties of elements are periodic functions of their atomic numbers. –The elements in the periodic table are arranged according to Periodic Law (why He is over N.G.s) c 1869 c 1911

Back ©Bires, 2002 Slide 4 Bires, 2009 Octets! Octets: –filled s and p orbitals in the same, highest level. –Have noble gas-like configurations –Have special stability (atom’s goal). Both atoms and ions can have complete octets. Valence ElectronsValence Electrons –Electrons in the highest level (s and p) –Given, taken, shared in chemical reactions –creates trends in the properties of elements …

Back ©Bires, 2002 Slide 5 Bires, 2009 Periodic Trends – Atomic Radii As electrons are added to the outside of atoms, in the same period, the atom’s radius decreases. Why? As new shells are added, radius increases. Text Page 141 Smaller from left to right

Back ©Bires, 2002 Slide 6 Bires, 2009 Periodic Trends – Ionization Energy Ionization Energy - the energy required to strip an electron from an atom. As more electrons are added to a shell, it’s more difficult to remove them. (More protons pulling inward) Easier to remove electrons from larger atoms. Text Page 143 Larger from left to right

Back ©Bires, 2002 Slide 7 Bires, 2009 Period Trends – Electronegativity Electronegativity (electron affinity) –an atom’s ability to attract electrons –Negative electron affinity = atom wants e -. –Decreases down a group Text Page 147 Larger from left to right

Back ©Bires, 2002 Slide 8 Bires, 2009 Ionic Radii +  - attraction determines the atom’s radius. An electron is added to a nonmetal atom : –Anion is formed. –Anions are larger than their neutral atom An electrons is removed from a metal atom: –Cation is formed. –Cations are smaller than their neutral atoms ClCl - NaNa + Why? e-

Back ©Bires, 2002 Slide 9 Bires, 2009 Groups and their Properties Recall: –elements in the same group have similar properties due to similar electron configurations. Learn the following group-families and their basic chemical and physical properties: –Alkali Metals –Alkaline-Earth Metals –Transition Metals –Main-Block Elements –Noble Gasses –Rare-Earth Elements

Back ©Bires, 2002 Slide 10 Bires, 2009 Group 1 (+1) Alkali Metals (s) soft, highly reactive metals. Lustrous –will reflect light Electrically Conductive –able to pass a charge through the material. –often found in lights, batteries, and electrolytes. Low melting points Low density.

Back ©Bires, 2002 Slide 11 Bires, 2009 Group 2 (+2) Alkaline-Earth Metals (s) Properties are similar to group 1 elements, but are: Harder Less reactive than Group 1 elements. –(These elements are still very reactive.) Lustrous Electrically Conductive Higher melting points than Group 1 metals. More dense than Group 1 metals.

Back ©Bires, 2002 Slide 12 Bires, 2009 Groups 3-12 (various) Transition Metals (d) This is where we find most metals, including the coinage metals. Lustrous Electrically Conductive Malleable –able to be shaped and formed, and hold that shape. Ductile –able to be drawn into wires Very hard Very dense High melting points

Back ©Bires, 2002 Slide 13 Bires, 2009 Group (+4  -4) Main-Block Elements (p) The most varied elements. –Liquids, gasses, and solids can be found in this group. Have widely varied properties Includes Metalloids –elements having properties of both metals and non metals. Most elements necessary to living things are found in this section. Includes Halogens –Group 17 gasses and liquids F, Cl, Br, I, At –are very reactive due to very high electron affinities.

Back ©Bires, 2002 Slide 14 Bires, 2009 Group 18 (0) Noble Gases (p) MostlyMostly unreactive. All have filled octets. Near zero electron affinity Very high ionization energies. Noble gasses make up a trace amount of our atmosphere –are mined from pockets of gases in the oceans. When electrically charged: –noble gases produce brilliant plasmas, often used in signs.

Back ©Bires, 2002 Slide 15 Bires, 2009 f – Group (various) Rare earth metals (f) Very heavy, dense (large nuclei) radioactiveMost are radioactive. Lanthanides –The first row, starting with lanthanum ( 57 La) –(4f elements) Actinides –The second row, starting with actinium ( 89 Ac) –(5f elements) Transuranium elements –All elements after Uranium 92 U ( 93 Np on) are artificial. End of Chapter 5

Back ©Bires, 2002 Slide 16 Bires, 2009 CCSD Syllabus Objectives 6.1: Groups and Families 6.2: Periodic Law 6.3: Periodic Properties-Atomic Structure 6.4: Periodic Properties-Periodic Law 6.5: Groups and Trends 6.6: Metals, Nonmetals, Metalloids 6.7: Trends-atomic structures 6.8: Electron config-p-table location 7.4: Oxidation numbers