Sign In Register If you like us, please share us on social media . The latest UCD Hyperlibrary newsletter is now complete, check it out. ChemWiki BioWiki GeoWiki StatWiki PhysWiki MathWiki SolarWiki Periodic Table of the Elements Reference Tables Physical Constants Units & Conversions Lab Techniques Inorganic Chemistry Descriptive Chemistry s-Block Elements Group 1: The Alkali Metals Articles ChemWiki: The Dynamic Chemistry E-textbook > Inorganic Chemistry > Descriptive Chemistry > s- Block Elements > Group 1: The Alkali Metals Group 1: The Alkali Metals Table of 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. Outside Links 9. References 10. Contributors 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 , though listed in Group 1 due to its electronic configuration, 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 basic solutions (pH>7), which are also called alkaline solutions. Properties and Facts About Alkali Metals Alkali metals are among 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 have an oxidation state of +1. These metals are characterized by their soft texture and silvery color. They also have low boiling and melting points and are less dense than most elements. Lithium, sodium, and potassium float on water because of their low density. All these characteristics can be attributed to these elements large atomic radii and weak metallic bonding. Group 1 elements have a valence electron configuration of ns1 and are good reducing agents (they are easily oxidized). All of the alkali metals are found naturally in nature, but not in their pure forms. Most combine with oxygen and silica to form minerals in the Earth; they are readily mined because they have relatively low densities and do not sink. Alkali Metal Reactions Reactions with hydrogen All alkali metals react with hydrogen to form hydrides as follows: Reactions with water Alkali metals and water react violently to form strong bases and hydrogen gas according to the following general reaction: where M denotes an alkali metal. An example involving sodium is given below: The 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 the hydrogen gas, resulting in an explosion like the one shown below: Reactions with halogens Alkali metals and halogens combine to form ionic salts with the general reaction: where M represents an alkali metal and X represents a halogen. For example Reactions with nitrogen Only lithium reacts with nitrogen at room temperature as follows: Reactions with oxygen Alkali metals form multiple types of oxides, peroxides and superoxides when combined with oxygen: Oxide ion: O2- compounds generally take the form M2O: e.g. Li2O Sodium forms Peroxides Peroxide Ion: O22- compounds generally take the form M2O2: e.g. Na2O2 Potassium, Cesium, and Rubidium form superoxides Superoxide ion: O2- compounds generally take the form MO2: e.g. KO2 Trends Electronegativity and Ionization energy increase across a period and up the group. Alkali metals have the lowest electronegativity and ionization energy Francium is the least electronegative element. Atomic radius increases from right to left across a period and down the group. Francium is the largest element Boiling points and melting points increase from the bottom of the group to the top of the group. Lithium and francium have the highest and lowest boiling points, respectively, in Group 1. Flame Colors Each alkali metal has a specific, characteristic flame color. The colors are caused by the difference in energy among the valence shells of s and p orbitals (not d-d transitions), which corresponds to wavelengths of visible light. When the element is introduced into the flame, its outer electrons are excited to higher-energy orbitals. The electrons then relax back to lower-energy orbitals, emitting energy in the form of light. The different colors of light depend on how much energy or how far the electron falls to a lower energy level. The alkali metals bright flame colors make them useful in firework manufacturing. Each has a unique color and is easily identifiable . Lithium Sodium Potassium Group 1 Element Flame Color Lithium Crimson Sodium Golden Yellow Potassium Red/Violet Rubidium Blue/Violet Cesium Blue/Violet 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 Soft metal Low ionization energy Electron configuration: [He]2s1 Often used in rechargeable batteries. Including 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 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 Sodium chloride is an important part of human diet Also used during winter months to control the ice on the road. Potassium Named after the word Potash 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 earths crust Oxidizes easily Lavender flame color Electron configuration: [Ar]4s1 Used mostly to produce chemicals, such as fertilizers for use in agriculture. 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 long 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 Highly radioactive Hardly any occurs naturally in the earths crust Atomic number: 87 Electron configuration: [Rn]6s1 Heaviest and most electropositive metal Has the lowest boiling point Melts at low temperatures. Most reactive of 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: 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. Complete and balance the following equation: 10. Compounds of the form M2O2 are formed from an alkali metal and what kind of oxygen ion?. Answers 1. The melting point and boiling point generally decrease down Group 1 Alkali Metals, so sodium has a higher boiling point (97.72°C) than francium (27°C). Atomic size increases as you move down the group and the larger the atom, the greater the distance between neighboring atoms in a metal lattice. This results in a weaker lattice energy and lower thermal energy to separate the atoms (lower melting point) 2. False. Group 1 and 2 form ionic hydrides. P block elements forms molecular hydride and nitrogen is in P block. 3. [Kr] 5s1 4. K, Rb and Cs. 5. 6. Lithium 7. False. Rubidium is a stable element (or at least has stable isotopes) 8. False. Only lithium reacts directly with nitrogen 9. 10. Peroxide ion: O22- 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. 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
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