Alkali Metals

Alkali metals are group 1 elements, including lithium, sodium, potassium, rubidium, cesium, and francium. Francium is radioactive and has no stable isotopes.

All alkali metals are unusually soft and share metallic properties, such as high electrical and thermal conductivity. Moving down the group, the mass, density, and atomic radii increase, while the melting points and ionization energies decrease.

The electron configuration of these elements implies that the valence shell has only one electron.

Their low ionization energies indicate that alkali metals readily lose electrons to become cations with a noble gas configuration. This also explains why alkali metals are excellent reducing agents, with lithium being the least reactive and cesium the most.

Alkali metals react vigorously with nonmetals, such as halogens, to form salts. The reaction of sodium metal with chlorine gas is highly exothermic and releases sparks and heat. The intensity of the reaction increases down the group as the ionization energies of the alkali metals decrease.

Alkali metals react vehemently with water to generate hydrogen gas and a solution of alkali metal hydroxide like potassium hydroxide, which is a base often used in soap making.

The reaction becomes more violent for the heavier alkali metals given their lower ionization energies. The heat produced during the reaction may even ignite the released hydrogen gas leading to fire or an explosion. 

Alkali metals can also react with hydrogen to form alkali metal hydrides, often used as strong bases. In this reaction, the hydrogen atom gains an electron and is present as the hydride ion. 

Due to their high reactivity, alkali metals oxidize easily upon exposure to air and are therefore stored in mineral oils. 

When alkali metal salts are placed in a flame and reduced to their gaseous metal atoms, they emit characteristic colors.  

The heat excites the valence electron to a higher energy level. When the excited electrons return to the ground state, energy is emitted in the form of radiation in the visible region. The emission spectrum of each element is unique and used to identify the element qualitatively.