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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.
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.
Reactions with hydrogen
All alkali metals react with hydrogen to form hydrides as follows:
\[2K(l) + H_2(g) \rightarrow 2KH(s)\]
Reactions with water
\[2M(s) + 2H_2O \rightarrow 2MOH(aq) + H_2(g)\]
where M denotes an alkali metal. An example involving sodium is given below:
\[2Na(s) + 2H_2O \rightarrow 2NaOH(aq) + H_2(g)\]
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
where M represents an alkali metal and X represents a halogen. For example
\[2Na(s) + Cl_2(g) \rightarrow 2NaCl (s)\]
Reactions with nitrogen
\[6Li(s) + N_2(g) \rightarrow 2Li_3N(s)\]
Reactions with oxygen
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|
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