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What are the Alkali Metals?The word “alkali” comes from Arabic, meaning “ashes of the saltwort”. In chemistry, it refers to a base that can dissolve in water. The alkali metals are all members of group 1 on the periodic table, minus hydrogen. This is the first column of the periodic table. They include lithium, sodium, potassium, etc. They all have one electron in their outer shell, which results in weak metallic bonding. These metals have very similar properties and group trends. Alkali metals have been known for a long time. In 1807, Sir Humphry Davy, soon after Volta first invented a battery, isolated sodium and potassium metal by electrolysis of molten sodium hydroxide and potassium hydroxide. Properties of the Alkali MetalsThe group 1 elements are all shiny, soft, and highly reactive. They can easily be cut with a knife. Because of their weak metallic bonding, they have lower melting points than other metal groups. They react quickly with air, and violently with water. They are usually stored under argon, or in mineral oil. The heavier elements react more violently with water, but even sodium can cause a large explosion if sufficient quantity is used. Most textbooks explain the violent reaction as hydrogen catching on fire. However, recent research shows that it is in fact not hydrogen, but a Coulomb explosion responsible for the explosive behavior in water. All of them have a very low density, and in fact lithium, sodium, and potassium float on water. They also have low electronegativities, low first ionization energies, but higher second ionization energies. Because the outer s electron is easily excited, these metals tend to have very distinctive flame colors. Rubidium has a striking red-violet flame color. Of the 5 non-radioactive alkali metals, cesium has the lowest melting and boiling point, the highest density, the largest atomic radius, and the highest reactivity. It has the lowest electronegativity and the lowest first ionization energy. List of all Alkali MetalsThe alkali metals include lithium, sodium, potassium, rubidium, cesium, and francium. Alkali Metal ChemistryAlkali metals form compounds almost exclusively in the +1 oxidation state. The reaction of these metals with water produce hydrogen and the corresponding hydroxide in solution. When exposed to air, these metals, particularly potassium, can form unstable peroxides and superoxides over time, which can explode in the right circumstances. Lithium gets a layer of lithium nitride when exposed to air. They react easily with most non-metals, including the halogens. The oxides and hydroxides form extremely basic solutions in water, which are highly corrosive. Most of their compounds are soluble, with lithium fluoride being an exception. Why are the Alkali Metals Reactive?The alkali metals are so reactive, due to a number of factors. Their low first ionization energy, combined with the fact they have just 1 electron to donate to get to a stable full shell state, makes them so reactive – even more so as their atomic radium gets larger. Fun or interesting facts about the Alkali Metals
Further ReadingHalogens Water-reactive substances[1] are those that spontaneously undergo a chemical reaction with water, as they are highly reducing in nature.[2] Notable examples include alkali metals, lithium through caesium, and alkaline earth metals, magnesium through barium. Some water-reactive substances are also pyrophoric, like organometallics and sulfuric acid, and should be kept away from moisture. The use of acid-resistant gloves and face shield are required and should be handled in fume hoods.[3] Such substances are classified as R2 under the UN classification system and as Hazard 4.3 by the United States Department of Transportation. In an NFPA 704 fire diamond's white square, they are denoted as "W̶". All chemicals that react vigorously with water or liberate toxic gas when in contact with water are recognized for their hazardous nature in the 'Approved Supply List,'[4] or the list of substances covered by the international legislation on major hazards[5] many of which are commonly used in manufacturing processes. Alkali metals[edit] Reaction of sodium (Na) and water Reaction of potassium (K) in water The alkali metals (Li, Na, K, Rb, Cs, and Fr) are the most reactive metals in the periodic table - they all react vigorously or even explosively with cold water, resulting in the displacement of hydrogen. The Group 1 metal (M) is oxidised to its metal ions, and water is reduced to hydrogen gas (H2) and hydroxide ion (OH−), giving a general equation of: 2 M(s) + 2 H2O(l) ⟶ 2 M+(aq) + 2 OH−(aq) + H2(g) [6]The Group 1 metals or alkali metals become more reactive in higher periods of the periodic table. Alkaline earth metals[edit]Group 2: Alkaline earth metals The alkaline earth metals (Be, Mg, Ca, Sr, Ba, and Ra) are the second most reactive metals in the periodic table, and, like the Group 1 metals, have increasing reactivity in the higher periods. Beryllium (Be) is the only alkaline earth metal that does not react with water or steam, even if the metal is heated red hot.[7] Additionally, beryllium has a resistant outer oxide layer that lowers its reactivity at lower temperatures. Magnesium shows insignificant reaction with water, but burns vigorously with steam or water vapor to produce white magnesium oxide and hydrogen gas: Mg(s) + 2 H2O(g) ⟶ MgO(s) + H2(g)A metal reacting with cold water will produce metal hydroxide. However, if a metal reacts with steam, like magnesium, metal oxide is produced as a result of metal hydroxides splitting upon heating.[8] The hydroxides of calcium, strontium and barium are only slightly water-soluble but produce sufficient hydroxide ions to make the environment basic, giving a general equation of: M(s) + 2 H2O(l) ⟶ M(OH)2(aq) + H2(g) [9]Reactivity series of metals[edit]
Hydrogen is always produced when a metal reacts with cold water or steam.[10] References[edit]
Are alkali metal reactive with water?Alkali metals react with water to produce heat, hydrogen gas, and the corresponding metal hydroxide. The heat produced by this reaction may ignite the hydrogen or the metal itself, resulting in a fire or an explosion. The heavier alkali metals will react more violently with water.
What is the order of reactivity of alkali metals with water?Lithium sodium and potassium all react vigorously with water. Alkali metals need to be stored under oil to prevent them reacting with the oxygen and water vapor in the air. The reactivity of the alkali metals increases down the group. Potassium reacts more vigorously than sodium and lithium is the least reactive.
What alkali metal is least reactive with water?Concept: The alkali metals are soft and silvery. They are also the most reactive metals having the lowest ionization energies. They react readily with water, lithium being the least reactive and potassium the most.
What alkali metal is most reactive?The reactivity of alkali metals increases from the top to the bottom of the group, so lithium (Li) is the least reactive alkali metal and francium (Fr) is the most reactive.
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Which alkali metal is most reactive with water
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