General Characteristics of Compounds of Alkali Metals
Table of Contents
Group 1 elements of the periodic table are known as Alkali Metals. It includes lithium, sodium, potassium, rubidium, cesium, and francium. They are also known as Active Elements.
Fig. 1: Position of Alkali Metals in a Periodic Table (pink in the left)
General Characteristics of Alkali Metals are as follows:
- Alkali metals are soft metals due to weak metallic bonding. They can be easily cut via knife. The hardness of the alkali metals decreases down the group.
- They have low melting and boiling points.
- They are highly reactive metals. They are kept in certain solutions such as kerosene oil to prevent their reactivity in the atmosphere.
- The energy required to remove an electron from the outermost shell is known as Ionization Energy. Alkali metals has lower first ionization energy but higher second ionization energy.
- Sodium is the most abundant metal. Francium is rarely found as it is radioactive in nature.
- They produce different colors with flame test. Lithium gives red color,
- Reaction of alkali metals with air forms oxides.
Li(s)+O2(g) → 2Li2O(s)
- They also form superoxides and peroxides in air.
Na(s)+O2(g) → 2Na2O
The peroxides are diamagnetic (no unpaired electrons) in nature. But superoxides are paramagnetic (unpaired electrons) in nature.
2Na + 2H2O → 2NaOH + H2,
Na2O + 2H2O → 2NaOH
Na2O2 + 2H2O → 2NaOH + H2O2
2KO2 + 2H2O → 2KOH + H2O2 + O2
- All monoxides are basic in nature. They form hydroxides when treated with water.
- Hydroxides of all alkali metals are strong bases such as sodium hydroxide.
- Alkali metals react with halogens to form alkali halides.
Na(s) + Cl2(g) → 2NaCl(s)
- Alkali metals also form alkali carbonates. Out of all alkali metals, only sodium form bicarbonates known as sodium bicarbonates (NaHCO3).
- Alkali metals also reacts with nitrates, such as sodium nitrate (NaNO3). Alkali nitrates on heating form nitrites.
2NaNO3 → 2NaNO2+O2
- Alkali metals reacts with hydrogen to form alkali hydrides. Lithium hydride when reacts with aluminum chloride form lithium aluminum chloride which is a strong reducing agent.
4LiH + AlCl3 → LiAlH4+ 3LiCl
- They are soluble in polar solvents.
- The hydration enthalpies of alkali metals decrease from top to bottom in a group.
Fig. 2: Summary of General Characteristics of Alkali Metals
- All alkali metals dissolve in liquid ammonia to give deep blue solutions. This reaction produces ions which are conducting in nature. The blue color of the solution is due to the formation of ammoniated electron which absorbs energy in the visible region of light. This imparts blue color to the solution.
M + (x + y) NH3 → M+ (NH3)x + e- (NH3)y
- All alkali metals forms salts with oxo-acids. Oxoacid is a compound with hydrogen, oxygen, and atleast one other element that can dissociate to produce hydrogen ion.
- Electronegativity decreases from lithium to francium. So, lithium has highest electronegativity.
- Nuclear charge decrease from top to bottom as compared to left to right in a column.
- They can attain noble gas configuration after losing their valence electron.
- They are electropositive in nature. When moving from lithium towards francium, metallic character increases.
- Out of all alkali metals, only lithium reacts with non-metal such as nitrogen to form lithium nitride, LiN3.
- They can form alloys.
- The most common method used for the separation alkali metals is chromatographic techniques.
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