General Chemistry/Chemistries of Various Elements/Group 1

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Alkali Metals

Sodium metal is soft enough to be cut with a knife.

The alkali metals are the elements in Group 1 (1A). They are lithium, sodium, potassium, rubidium, cesium, and francium.

These elements are best marked by their reactivity. Physically they are soft, shiny (when freshly prepared) solids with low melting points; they conduct electricity well. They all have one valence electron that they lose easily to almost any electronegative substance. Alkali metals are never found in their elemental form outside the lab because they are too reactive. Even the smallest amount of oxygen or water would react with the metal. For this reason, alkali metals have no structural use. They must be kept under inert liquids such as kerosene or in inert gases (nitrogen suffices for any of these elements other than lithium).

Alkali metals have many uses in both biological life and industry. Francium, however, is radioactive and decays rapidly to other elements, so it has no commercial use and its chemical properties are vaguely understood.

All oxidize easily to the +1 oxidation state.

Safety

Leave experiments with alkali metals to the experienced chemists.

Reactions

Alkali metals react violently with water, halogens, and acids. The reactions release surprising amounts of heat and light. In a chemical equation, alkali metals are represented with an M. Here are some example equations:

 ${\displaystyle 4{\hbox{M}}_{(s)}+{\hbox{O}}_{2(g)}\to 2{\hbox{M}}_{2}{\hbox{O}}_{(s)}}$ Alkali metals react with oxygen to form oxides, which have a duller appearance and lower reactivity. The oxides are much less reactive than the pure metals. ${\displaystyle {\hbox{M}}_{2}{\hbox{O}}_{(s)}+{\hbox{H}}_{2}{\hbox{O}}\to 2{\hbox{MOH}}_{(aq)}}$ However, the oxides do react vigorously with water to form a hydroxide. The resulting hydroxides of these elements dissociate completely in water to form some of the strongest bases known. "Lye" is an industrial-strength base, which is sodium hydroxide (NaOH). ${\displaystyle {\hbox{NaOH}}_{(aq)}+{\hbox{HCl}}_{(aq)}\to {\hbox{NaCl}}_{(aq)}+{\hbox{H}}_{2}{\hbox{O}}_{(l)}}$ These hydroxides react readily with acids to form water and their corresponding alkali salt in a neutralization reaction. ${\displaystyle 2{\hbox{M}}_{(s)}+2{\hbox{H}}_{2}{\hbox{O}}\to 2{\hbox{MOH}}_{(aq)}+{\hbox{H}}_{2(g)}}$ The pure alkali metal can also react directly with water. In this case, the metal is a basic anhydride. Gaseous hydrogen is released, which is flammable. ${\displaystyle 2{\hbox{M}}_{(s)}+{\hbox{Cl}}_{2(g)}\to 2{\hbox{MCl}}_{(s)}}$ Exposing an alkali metal to a halogen will cause an extremely exothermic reaction that results in an ionic salt.

Almost every salt of an alkali metal is highly soluble in water. They form conducting solutions, proving their ionic nature.

Flame Tests

When burned in a flame, the alkali metals give off a unique color that can be used to identify them.