Alkali Metals
The alkali metals are in the first group of the periodic table. They are highlighted in orange on the table below.
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The alkali metals are a soft metallic solid, and they all have metal properties such as, high thermal and electrical conductivities, and a silver like luster. Two of the most common elements on Earth are Sodium (Na) and potassium (K). The human body contains both of these elements. As you go down the group the melting point decreases, the density increases, and the atomic radius increases. Each one of these elements have one valence electron in the s orbital. The alkali metals have the lowest ionization energy of all the periods of the table. They lose one electron and get a +1 charge. Because of this low ionization energy the alkali metals are some of the most reactive elements on the table. One might be familiar with the explosive results if an alkali metal is placed in water. When they react with water they produce H gas and hydroxides of the alkali metals (XOH) When they react with sulfur they create sulfides.
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In 1987 a certain chemistry teacher who will remain nameless for security purposes, had an interesting encounter with the reaction of sodium and water. The students the urged him to put a larger piece of Na into the beaker. Being young and inexperienced he obeyed they commands and tossed it in. To his dismay a spark ignited the cloud of explosive Hydrogen gas which blew him against the blackboard. "As I came to my first thought was for the safety of my students," he later told me in an interview, "I was worried That one of my students was sprayed by the molten Na in the eye." As he lay on the ground he saw that the water had somehow blasted onto the 10 foot roof and the Na continued to react. To this day he vows to never put that much Na into the beaker again, much to his students dismay. Also in 1987 a piece of potassium (K) flew out of the beaker and hit him on the hand. He is now scarred for life. I dedicate this page to those poor skin cells that were fried in that tragic accident. Also this page is dedicated to that teacher an how he continues to this day to to teach young minds about the magic of chemistry.
Flame Tests
A great way to identify the alkali metals is through flame tests. Each alkali metal gives off a unique color flame when burned. This happens because the metals are turned into gases in the flame. The valence electrons are excited and jump up into higher energy levels, the color you see is the electrons returning to ground state. This event has been harnessed for human use, when sodium electrons are excited a yellow color is produces (wavelength = 589 nm). Sodium vapor is put in lamps and used to for things like highway lighting
This is a flame test with sodium:

This is lithium

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All information obtained from Chemistry The Central Science By Brown, LeMay, and Bursten