What are Alkali Metals?

Elements Lithium, Sodium, Potassium, Rubidium, Caesium, Francium which forms Group 1 of Periodic Table are called Alkali Metals. For all of these metals, their electronic configuration is a single outer shell s-electron plus an inert noble gas configuration. For example – Lithium electronic configuration is [H]2s1 and for Sodium it’s [Ne]3s1 .
In general, Electronic Configuration of these Alkali Metals can be written as [Some Noble Gas] ns1 where n can be an integer 2 to 7.

Atomic Symbols of Alkali Metals

Alkali MetalAlkali Metal Atomic Symbol
LithiumLi
SodiumNa
PotassiumK
RubidiumRb
CaesiumCs
FranciumFr

Atomic Numbers of Alkali Metals

Alkali MetalAtomic Number
Lithium3
Sodium11
Potassium19
Rubidium37
Caesium55
Francium87

Atomic Masses of Alkali Metals

Alkali MetalAtomic Mass
Lithium6.941 u
Sodium22.98977 u
Potassium39.0983 u
Rubidium85.4678 u
Caesium132.90545 u
Francium223 u

Atomic Radius of Alkali Metals

Alkali MetalAtomic Radius
Lithium152 pm
Sodium227 pm
Potassium53 pm
Rubidium290 pm
Caesium343 pm
Francium348 pm

In the above table pm means Pico Metre, 1 pico metre equals 10-12 metres mathematically

Looking at the above table, it’s clear that amongst all of Alkali Metals, Francium have largest atomic radius(348 pm) while Potassium have lowest(53 pm). The general trend of Atomic Radius amongst Alkali Metals in decreasing order is Francium, Caesium, Rubidium, Sodium, Lithium, Potassium.

Melting Points of Alkali Metals

Alkali MetalMelting Point
Lithium180.5 °C
Sodium97.81 °C
Potassium63.28 °C
Rubidium39.3 °C
Caesium28.44 °C
Francium27 °C

As clearly visible from above table lithium have highest melting point(180.5 °C) while Francium have lowest(27 °C) amongst all of Alkali Metals. In general, melting point amongst Alkali Metals decreases in order Lithium, Sodium, Potassium, Rubidium, Caesium, Francium.

Boiling Points of Alkali Metals

Alkali MetalMelting Point
Lithium1,330 °C
Sodium882.9 °C
Potassium760 °C
Rubidium688 °C
Caesium670.8 °C
Francium676.8 °C

Seeing above it’s visible clearly that Lithium have the highest melting point(1,330 °C) while Rubidium have the lowest(688 °C) amongst all of Alkali Metals. Generally, Boiling Point amongst Alkali Metals decreases in order Lithium, Sodium, Potassium, Rubidium, Francium, Caesium.

Electronic Configurations of Alkali Metals

Alkali MetalElectronic Configuration
Lithium[He] 2s1
Sodium[Ne]3s1
Potassium[Ar]4s1
Rubidium[Kr] 5s1
Caesium[Xe] 6s1
Francium[Rn] 7s1

First Ionization Energies of Alkali Metals

Alkali MetalIonization Energy in KJ mol-1
Lithium520 KJ mol-1
Sodium496 KJ mol-1
Potassium419 KJ mol-1
Rubidium403 KJ mol-1
Caesium376 KJ mol-1
Francium380 KJ mol-1

Amongst all of Alkali Metals, Lithium have highest first ionization energy(520 KJ mol-1) while Caesium have lowest(376 KJ mol-1). General trend of first ionization energy amongst Alkali Metals in decreasing order is Lithium, Sodium, Potassium, Rubidium, Francium, Caesium.

Electropositivity of Alkali Metals?

All of these Alkali Metals are highly Electropositive meaning these can easily be converted to their respective cation except hydrogen which needs 1310 KJ mol-1 for it to be converted to hydrogen ion.

For example – In order to convert lithium(Li) to lithium cation(Li+) only 520 KJ of energy is required per mole.
In general, going down in Group 1(Alkali Metals) in the periodic table Electropositivity of metals increases as First Ionization Energy is decreasing.

Lesser the First Ionization Energy of metal is, more it’s Electropositive as compared to other Alkali Metal

So based upon First Ionization Energies of Alkali Metals, the Electropositivity trend(in increasing order) of Alkali Metals is Lithium, Sodium, Potassium, Rubidium, Francium, Caesium. So Caesium is the most electropositive and Lithium is the least electropositive metal amongst all Alkali Metals.

Reactions of Alkali Metals

Alkali Metals Reaction with Oxygen

Alkali Metals are highly reactive because they have low ionization energies. Alkali Metal can react with oxygen to produce respective oxide. For example – Sodium reacts with Oxygen to produce Sodium Oxide. Similarly, other elements also react with Oxygen to produce oxides.

Below are Balanced Chemical Equations showing, reactions of Alkali Metals with oxygen.

    \[ 4\mathrm{Li}+\mathrm{O}_{2} \rightarrow 2 \mathrm{Li}_{2} \mathrm{O}\]

    \[ 4\mathrm{Na}+\mathrm{O}_{2} \rightarrow 2 \mathrm{Na}_{2} \mathrm{O}\]

    \[ 4\mathrm{K}+\mathrm{O}_{2} \rightarrow 2 \mathrm{K}_{2} \mathrm{O}\]

    \[ 4\mathrm{Rb}+\mathrm{O}_{2} \rightarrow 2 \mathrm{Rb}_{2} \mathrm{O}\]

    \[ 4\mathrm{Fr}+\mathrm{O}_{2} \rightarrow 2 \mathrm{Fr}_{2} \mathrm{O}\]

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