Here, we learn chemistry of alkali metals(group 1 elements) of s block. Occurrence. reactions, physical properties of group 1 elements are discussed in this tutorial. Usually, group 1 elements of s block are very reactive and exist as compounds. Their only valence is one.
In room temperature condition... Hydrogen exists as H2 gas and rest of others are solid.
Those elements have only one electron in their last shell
commonly, we can show it as 1s2 2s22p6.... ns1
Na - 1s2 2s22p6 3s1
K - 1s2 2s22p6 3s23p6 4s1
alkali metals are very reactive due to existence of only one electron in the last shell.
Lot of compounds of these elements are soluble in water.
Most solids of alkali metal compounds take white colour.
Li, Na, K, Rb, Cs reacts with water and H2(g)is emitted and relevant hydroxide of metal is formed.
Reaction of K with water is a highly flammable.
Alkali metals react with strong acids (HCl , HNO3 , H2SO4) and H2 will be omitted, relevant salt will be produced.
Metal hydride (H-) is given.
Those ionic hydrides have H-. These ionic hydrides react with compounds
which can supply H+ ions. Therefore these hydrides behave as strong reducing agents.
So they alkali metal hydrides react with water, alcohols,
ammonia and alkyne to eliminate H2 gas.
Liquid Li reacts(burning) with O2(g) and make Li2O.
Na , K reacts with Oxygen and make relevant Oxide of metal.
When Na, K, Rb, Cs is heated in a hot air stream, peroxide are formed.
Also K,Rb can make super oxides
Above oxides can react with water and make hydroxides.
group IA elements react with halogen and form halides.
Na reacts S and give sulfide when heat is supplied.
Those sulfides can react with dilute acids. And H2S gas is released.
Na Reacts with NH3 and H2 gas is emitted giving NaNH2.
Na Reacts with P when heat is available.
Na reacts with H2S to give sulfide and H2 gas.
The alkali metal halides are high melting colourless crystalline solids.
Ex: NaCl , KBr
These alkali metal halides are prepared by the reaction of appropriate oxide, hydroxide or carbonate with aqueous hydrohalic acid (HF, HCl, HBr, HI)
Fluorides of alkali metals are most stable while iodides of alkali metals are least stable.
Melting and boiling points of alkali metal halides decreases with the increase in atomic mass of the halides as:
F- > Cl- > Br- > I-
Ex: Melting point of NaCl is higher than NaBr
For given halide ion, melting and boiling points of LiX is always less than NaX.
All alkali metal halide compounds are soluble in water exception of LiF. LiF is insoluble in water due to its high lattice energy because of small cation and small anion size. Other halide ions of lithium are soluble in ethanol, acetone, ethyl acetate. LiCl is soluble in pyridine. CsI has also low solubility due to smaller hydration energy of its two ions.
Alkali metals are electropositive metals. Therefore they form salts with oxo acids.
Oxo acids are those in which the acidic proton which is on a hydroxyl group with an oxo group attached to the same acid. Carbonic acid(H2CO3), sulfuric acid(H2SO4), phosphoric acid(H3PO4) are some examples.
The alkali metals form salts with all oxo acids. These alkali metal oxo salts are generally soluble in water and thermally stable. But Li2CO3 is not stable to heat and decomposes readily. LiHCO3 does not exist as a solid.
Carbonates of alkali metals are stable to heat (except Li). The stability of those carbonates are increased down the group.
LiHCO3 does not exist as a solid. Li2CO3 is not stable to heat as other alkali metal carbonates
Bicarbonates of alkali metals (except Li) decomposes into the carbonates, carbon dioxide and water.
KO2 - Orange
RbO2 - Brown
KO2 - Dark Orange
Li+ has very high polarizing power. Therefore LiCl is covalant in nature. Being covalent in nature, it is soluble in organic solvents.
Many compounds of alkali metals are soluble in water. But few of alkali metal compounds are insoluble in water specially some compounds of lithium. Lithium carbonate, lithium fluoride, lithium carbonate, lithium oxalate are sparingly soluble in water. Solubility of sodium bicarbonate is also less than potassium bicarbonate.
Written by : Heshan Nipuna
Last Edition : 09/10/2018
Related Topics to s Block Group 1 Elements - Alkali Metals