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1 Group 1: The Alkali Metals Group 1: The Alkali Metals Alkali metals are the chemical elements found in Group 1 of the periodic table. The alkali metals include: Lithium (Li), Sodium (Na), Potassium (K), Rubidium (RB), Cesium (Cs), and Francium (Fr). Hydrogen, while it appears to be listed within Group 1, is not included in the alkali metals since it rarely exhibits similar behavior. The word "alkali" received its name from the Arabic word "al qali," meaning "from ashes". These particular elements were given the name "Alkali" because they react with water to form hydroxide ions, creating a basic solution (pH>7). Solutions that have a pH greater than 7 are called alkaline solutions. Contents 1. Properties and Facts about Alkali Metals 2. Alkali Metal Reactions 3. Trends 4. Flame Colors 5. Elements of the Alkali Metal Group 5.1. Lithium 5.2. Sodium 5.3. Potassium 5.4. Rubidium 5.5. Cesium 5.6. Francium 6. Problems 7. Answers 8. External Video Links 9. Outside Links 10. References 11. Contributors Properties and Facts about Alkali Metals Alkali metals are known for being some of the most reactive metals. This is due in part to their larger atomic radii and low ionization energies. They tend to donate their electrons in reactions and often have an oxidation state of +1. These metals are characterized as being extremely soft and silvery in color. They also have low boiling and melting points and are less dense than most elements. Li, Na, and K float on water because of their low densities. All of these characteristics can be attributed to the large atomic radii and weak metallic bonding these elements possess. Group 1 elements have a valence electron configuration of ns1 and are good reducing agents (meaning they are easily oxidized). Alkali Metal Reactions 1) With Hydrogen: all alkali metals react with hydrogen to form hydrides 2K(l) + H2(g) → 2KH(s) 2 Group 1: The Alkali Metals 2) With Water: Alkali metals and water react violently to form strong bases and hydrogen gas. General Reaction: 2M(s) + 2H2O → MOH(aq) + H2(g) where M=alkali metal example: 2Na(s) + 2H2O → 2NaOH(aq) + H2(g) note: Reactivity with water increases as you go down the group. The explosive reaction of sodium with water. In this case, the exothermic reaction is enough to ignite hydrogen gas. 3) With Halogens: Alkali metals and halogens combine to form ionic salts General Reaction: M(s) + X(g)→ MX(s) where M=alkali metal and X=halogen example: Na+(s) + Cl-(g) → NaCl (s) 4) With Nitrogen: only Lithium reacts with Nitrogen at room temperature 6Li(s) + N2(g) → 2Li3N(s) 5) With Oxygen: Alkali metals form multiple types of oxides, peroxides and superoxides when combined with oxygen: Oxide ion= O2o compounds generally look like M2O 3 Group 1: The Alkali Metals ex. Li2O Sodium forms Peroxides 2o Peroxide Ion= O2 compounds generally look like M2O2 ex. Na2O2 Potassium, Cesium, and Rubidium form superoxides o Superoxide ion=O2 compounds generally look like MO2 ex. KO2 Trends Electronegativity and Ionization energy increase from LEFT TO RIGHT and BOTTOM TO TOP o Alkali metals have the lowest electronegativity and ionization energy o Francium is the least electronegative element. Atomic radius increases from RIGHT TO LEFT and TOP TO BOTTOM o Francium is the largest element Boiling points and melting points increase going BOTTOM TO TOP o Lithium has the highest boiling point and Francium has the lowest boiling point in Group 1. Flame Colors All alkali metals have their own specific flame color. The colors are caused by the difference in energy among the valence shell of s and p orbitals, which corresponds to wavelengths of visible light. When the element is introduced into the flame, its outer electrons are excited and jump to a higher electron orbital. The electrons then fall and emit energy in the form of light. The different colors of light depend on how much energy or how far the electron falls back to a lower energy level. For this reason, they are often used in fireworks. Each alkali metal has a unique color and is easily identifiable. Group 1 Element Flame Color Lithium Crimson Sodium Golden Yellow Potassium Red/Violet Rubidium Blue/Violet Cesium Blue/Violet 4 Group 1: The Alkali Metals Lithium Sodium Potassium Elements of the Alkali Metal Group Lithium named after the Greek word for stone (lithos) discovered in Sweden in 1817 Atomic number: 3 Atomic weight: 6.941 the lightest and least dense of all alkali metals highly reactive a soft metal has a low ionization energy Electron configuration: [He]2s1 Often used in rechargeable batteries. o Includes those used in cell phones, camcorders, laptop computers, and cardiac pacemakers. Sodium named after the Latin word for soda, Natria discovered in 1807 Atomic number: 11 Atomic weight: 22.9897 soft silvery metal. extremely reactive metal Electron configuration: [Ne]3s1 used in nuclear reactors because of its low boiling point. Sodium is reacted with chlorine to produce the ionic halide, NaCl o Sodium chloride is an important part of human diet It is used during winter months to control the ice on the road. 5 Group 1: The Alkali Metals Potassium named after the word Potash o Potash: means that Potassium is an element contained in the compound discovered in 1807 Atomic number: 19 Atomic Weight: 39.0983 one of the most abundant elements in the earth's crust oxidizes easily lavender flame color Electron configuration: [Ar]4s1 used mostly to produce chemicals, such as fertilizers for use in agriculture. o Potassium is an important nutrient needed for plant growth. Rubidium named after the Latin word for red, rubidius Atomic number: 37 soft metal reddish flame color Electron configuration: [Kr] 5s1. discovered in 1861 known to have about 26 isotopes very large half life at an estimated 49 billion years Cesium Atomic number: 55 forms a strong base with water Atomic Weight: 132.91 discovered in 1860 often used as a catalyst in various hydrogenation organic reactions low melting point Electron configuration: [Xe]6s1. Francium discovered in 1939 very radioactive hardly any Francium occurring naturally in the earth's crust Atomic number: 87 Electron configuration: [Rn]6s1 heaviest and most electropositive metal has the lowest boiling point o Melts at low temperatures. most reactive of the alkali metals group 6 Group 1: The Alkali Metals Problems 1. Which alkali metal has a higher melting point, Sodium (Na) or Francium (Fr)? Explain. 2. True or False. NH3 is an ionic hydride. 3. What is the electron configuration of Rubidium? 4. Which alkali metals form superoxides? 5. Complete and balance the following equation: Li2O2 + H2O → ? 6. Which element is the most electronegative: Francium, Potassium, or Lithium? 7. True or False: Rubidium has a very short half-life and decays quickly. 8. True or False: All alkali metals react with Nitrogen. 9. Balance the following equation: Li(s)+N2(g)→ ? 10. Compounds that generally look like M2O2 are formed with a metal and what kind of oxygen ion?. Answers 1. Sodium has a higher boiling point because it has a larger atomic radius that Francium. Greater atomic radius means a bigger molecule thus having a higher boiling point. 2. False. Group 1 and 2 form ionic hydrides. P block forms molecular hydride and Nitrogen is in P block. 3. [Kr] 5s1 4. K, Rb and Cs. 5. Li2O2 + H2O 2LiOH + H2O2 6. Lithium 7. False 8. False, only Lithium reacts with Nitrogen 9. 6Li(s)+N2(g)→2Li3N(s) 10. Peroxide Ion= O22- External Video Links The following website shows the explosive reaction of alkali metals and water. It's cool stuff! Check it out! http://video.google.com/videosearch?hl=en&q=alkali+metals&um=1&ie=UTF8&sa=X&oi=video_result_group&resnum=4&ct=title http://video.google.com/videoplay?do...66654801392897 Outside Links Alexander, M. Dale. "Reactions of the alkali metals with water: A novel demonstration (TD)." J. Chem. Educ. 1992, 69, 418. Birmingham, J. F., Jr.; Wood, W. H. "Apparatus for making spectral flames of the alkali and alkaline earth metals." J. Chem. Educ. 1936, 13, 240. 7 Group 1: The Alkali Metals Ciparick, Joseph D.; Jones, Richard F. "A variation on the demonstration of the properties of the alkali metals (TD)." J. Chem. Educ. 1989,66, 438. Dye, James L. "Alkali metal anions. An unusual oxidation state." J. Chem. Educ. 1977, 54, 332. Nelson, Arthur F. "Potassium soap-soft or hard?" J. Chem. Educ. 1948, 25, 379. References 1. Fresenius, C. Remigius. Manual Qualitative Chemical Analysis. J. Wiley & Sons, 1897. Page 430 2. Massey, A. G. Main Group Chemistry. London: Ellis Horwodd, 1990. Print. 3. Petrucci et al., General Chemistry, Principles & Modern Applications, by Macmillan Publishing Company,Ninth Edition,Page 877. Contributors Kellie Berman, Nilshita Devi