Alkali Metals

The six chemical element belonging to group IA of the periodic table are Lithium, Sodium, Potassium, Rubidium, Cesium, Francium.

They are named alkali metals as they form alkalies when reacted with water.
They represent alkali metals basically because they readily disband in H₂O to make their respective hydroxides, and are strongly alkaline in nature.
They form alkaline oxides.
The chemical element francium is radioactive.

The list of alkali metals are as follows,

• Lithium (Li)
• Sodium (Na)
• Potassium (K)
• Rubidium (Rb)
• Cesium (Cs)
  
• Francium (Fr)
  

Lithium forms mainly exist as silicate such as lepidolite [(Li,Na,K)₂Al₂,(SiO₃)₃ (F,OH)₂], spodumene [LiAl(SiO₃)₂] etc.
It is considered as the 35th most abundant element by mass,

Compounds of both Natrium (Na) and Kalium (K) have been known from the ancient times.
Both Natrium and Kalium are seventh and eighth most abundant elements by mass in the Earth's crust and they together make up over 4% of the Earth's crust by weight.
Sodium chloride (NaCl) and Potassium chloride (KCl) also occur in vast stretches of seawater.
Rock salt (NaCl) is considered as one of the major sources of sodium.
Potassium occurs mainly in the deposits of potassium chloride KCl (known as sylvite), which is nothing but a mixture of KCl and NaCl (also known as sylvinite) and also the double salt KCl.MgCl₂.6H₂O (carnallite).

Apart from these elements, Rubidium and Cesium are obtained as a by-product of the processing of element lithium.
Francium being the only radioactive element of group I does not freely in nature.

The metals which are present in group IA of the modern periodic table and are soft and have low-density, low-melting point and are highly reactive are known as alkali metals.

The properties of alkali metals are as follows

Periodic Table Alkali metals

The periodic table of alkali metals and their electronic configurations for the group I is covered below.
The alkali metals have one electron in their outermost 's' orbitals which is preceded by the respective noble gas configuration resulting in the general configuration of alkali metals written as [Noble gas] ns¹.
The symbol 'n' represents the valence shell.
The alkali metals electronic configurations are as follows:

Element	Symbol	Atomic Number	Electronic configuration
Lithium	Li	3	[He]2s1
Sodium	Na	11	[Ne]3s1
Potassium	K	19	[Ar]4s1
Rubidium	Rb	37	[Kr]5s1
Cesium	Cs	55	[Xe]6s1
Francium	Fr	87	[Rn]7s1

Ionization Energies

• Alkali metals have the lowest ionization energy in each period. The alkali metals ionization energies decreases gradually as we go down the group and this is due to their largest atomic size in their respective periods.
  
• The valence electrons in large sized atoms are held losely by nucleus and can be easily lost. This leads to low ionization energies and acquire the stable noble gas configurations. The atomic size usually increases while going down the group and thus the number of inner shells also gets increased. This leads to the increasing magnitude of screening effect resulting in the decrease in ionization energy down the group.

• The Alkali metals second ionization energies are also found to be very high. The removal of an electron from alkali metals results in the formation of monovalent cations as they have very stable electronic configurations.
  
• To remove the second electron from the acquired stable noble gas configurations It is very difficult, resulting in a very high second ionization energy values (IE₂).

Physical property	Li	Na	K	Rb	Cs
Ionization Energy I	520	496	419	403	376
KJ mol -1 II	7298	4562	3051	2633	2230

Melting and Boiling Points

All alkali metals are found to be very soft and they have low melting and boiling points.
Alkali metals have low binding energy in the metal crystal lattice as these atoms have only one valence electron. This results in the formation of metallic bonds which are not very strong and also alkali metals melting and boiling points decreases down the group.

Physical property	Li	Na	K	Rb	Cs
Melting point (K)	453.5	370.8	336.2	312.0	301.5
Boiling point (K)	1620	1154.4	1038.5	961.0	978.0

Density

The densities of alkali metals are found to be low when compared to other metallic element, with Li, Na and K being yet light than H₂O (K is lighter than Na).
Although, alkaline metal have tight packing of atoms in their lattice but the big size of their atoms makes them to have low density.

As we go down the group from element Li to Cs, even though there is a gain in atomic size, the overall gain in atomic weight covers more the gain in atomic size. The densities (mass volume) of alkali metals gradually increase from Li to Cs.
That Potassium is lighter than Sodium (Na) is because of the increased atomic size of Potassium (K).

Physical property	Li	Na	K	Rb	Cs
Density (g cm -1)	0.53	0.97	0.86	1.53	1.90

Electropositive or Metallic Character

For any element, the electropositivity is expressed in terms of the tendency of its atom to release or lose electrons

Almost all the alkali metals are very strongly electropositive or metallic in character.
Due to low ionization energies and the alkali atoms readily lose the valence electrons.
The ionization energies decreases down the group, and this leads to electropositive characteristics or electron releasing tendency, increasing down the group as well.

Physical property	Li	Na	K	Rb	Cs
Eo value (V)	- 3.03	- 2.71	- 2.93	- 2.93	- 2.92

Oxidation States

As the alkali metals have only one electron in their valence shell they exhibit an oxidation state of +1 in their compounds and can also lose the only valence electron to readily acquire the stable configuration of the nearest noble gas. 

These elements form monovalent ions, M⁺ (e.g., Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺). The second ionization energies being very high, they won't be able to form divalent ions. Hence the alkali metals are found to be univalent and form ionic compounds.

The alkali metals have very low ionization energies and thus even the energy from the Bunsen burner flame is enough to excite the electrons of any alkali metals to the higher energy levels.
The unstable excited state causes these electrons to return to their original energy levels. The return of these excited electrons to their ground levels also results in emitting extra energy, giving characteristic flame coloration.

The different colors of alkali metals could be explained on the basis of the amount of energy that is absorbed to reach the excitation levels of valence electrons.

Physical property	Li	Na	K	Rb	Cs
Flame color	crimson red	yellow	pale violet	violet	bluish

Photoelectric Effect

When light rays or electromagnetic radiations strikes the alkali metal surface, they start emitting electrons. This is better known as its photoelectric effect. This takes place as the alkali metals when exposed to light ejects electrons easily and this is due to the low ionization energies of alkali metals. 

Among the alkali metals, element Cesium has the lowest ionization energy and thus shows the maximum extent of photoelectric effect.

Nature of the Compounds

The alkali metal compounds are ionic in nature. Alkali metals can form cations readily by losing the valence electrons and this due to the low ionization energies and large atomic sizes. The alkali metals form ionic bonds with the non-metals of the 'p' block. The alkali metals react vigorously with water. The reaction between water and alkali metals is exothermic in nature.They react with water to form alkaline hydroxides. These hydroxides are strongly alkaline.Therefore they should be handled with care.Heavier alkali metals react more vigorously than that of the lighter alkali metals.


For example, cesium produces a larger explosion when dropped in water than potassium.

Lithium

1. The most important use of Lithium is in the manufacture of alloys.It is added to the alloys of magnesium to improve their tensile strength and resistance to corrosion.
2. Lithium compounds are employed to increase the fluidity of glass. Its carbonate is employed to increase the strength and resistance of glass.
3. Its is used as an oxidizer in the purification of nickel and copper.
4. Its citrate an salicylate are employed in the medicine for relieving gout since lithium urate is fairly soluble in water.
5. Its hydroxide is used in the manufacture of high quality lubricating gases which can with stand extreme variation of temperature.