Important Groups of the Periodic Table

1. The important groups (for the purposes of Chemistry 11) on the periodic table are groups 1, 2, 17, and 18. They are: Alkali Metals, Alkaline Earth Metals, Halogens, and Noble Gases. Be able to locate groups on the periodic table and describe some of their distinguishing properties. Important Groups of the Periodic Table (c) McGraw Hill Ryerson 2007

2. Noble Gases • Noble Gases are group 18 of the periodic table (very right-hand-side) • They are non-metals (they are to the right of the staircase) • They are very non-reactive (don’t form compounds or ions) because their valence shells are already full • Noble gases are the most stable (least reactive) of all elements because of the their full valence shells (c) McGraw Hill Ryerson 2007

3. Noble Gases, Cont’d. • High ionization energy and lowest melting points • Often used in lighting (they glow different colours when electricity is passed through them); “neon” lights don’t always have neon gas in them (c) McGraw Hill Ryerson 2007

4. Halogens • Halogens are group 17 on the periodic table • Halogens are non-metals because they are to the right of the staircase • Halogens are highly reactive (form new compounds easily) because they only need one more electron to fill their valence shell. It’s pretty easy to find just one electron. • Charge of 1- when they ionize (gain one electron to get a full valence shell) • All halogen atoms have 7 valence electrons (c) McGraw Hill Ryerson 2007

5. Halogens, cont’d. • Unlike alkaline and alkali earth metals, as you move down the periodic table, the halogens get less reactive (halogens get more reactive as you move up the periodic table) • All halogens are non-metals, but iodine is a solid, bromine is a liquid, and the rest are gases • They are all diatomic (eg. Cl2 and F2) • They are highly reactive because they only need one electron to form a full valence shell • They especially are inclined to form compounds with alkali metals (eg. NaCl) and alkaline earth metals (e. g . CaBr2) • Used in halogen lamps (obviously) along with the noble gases (c) McGraw Hill Ryerson 2007

6. Alkali Metals • Group 1 • The most reactive metals • Get more reactive the closer they get to the bottom of the periodic table; react vigorously with water and acids. • All other metals are less reactive than alkali metals • Have an ion charge of 1+ because need to lose only one electron to have a full valence shell (one electron in the outer shell) • Called “alkali” metals because they form bases (a. k. a. “alkaline compounds”), such as NaOH and KOH • When metals do react with acids, H2 gas is usually released. 2HCl + K  KCl + H2 See pages 238 - 239 (c) McGraw Hill Ryerson 2007

7. Akali Metals, cont’d. • Largest atomic radii of any atom in their respective periods because the one valence electrons is just loosely bound • Low ionization energy because it’s easy to remove that one loosely-bound electron • Often form compounds with halogens (e. g. LiF), donating their one valence electron to fill the one empty valence spot that the halogen has (c) McGraw Hill Ryerson 2007

8. Alkaline Earth Metals • Group 2 • More reactive than other metals (but less reactive than the alkali metals) • Reactivity increases moving down the periodic table • Form salts with halogens (e. g. CaCl2) • Have an ion charge of 2+ because lose 2 electrons to have a full valence shell (c) McGraw Hill Ryerson 2007

9. Alkaline Earth Metals, cont’d. • Easily lose their 2 valence electrons to form ions (low ionization energies) • Slightly smaller atomic radii than alklai metals in the same period (row) • Also form alkaline solutions (bases), such as Mg(OH)2 and Ca(OH)2 • Called alkaline EARTH metals because they are found in the EARTH’S crust (c) McGraw Hill Ryerson 2007

10. In Summary • Each group of elements share similar characteristics to other elements within their same groups • These shared properties are due solely to the fact that all members of one group share the same number of valence electrons • Conclusion: the number of valence electrons in an element determines the properties of that element (c) McGraw Hill Ryerson 2007