Alkali metals

Why are they called alkali metals?

The elements of this group are collectively called alkali metals, since they form strongly alkaline oxides and hydroxides. Fr is a radioactive element in this group.

Similarities in physical properties of alkali metals

!. physical state
2. atomic volume, atomic and ionic radii
3. Density
4. Melting and boiling points
5. ionization energies
6. electropositive character
7. Reducing properties
8. electronegativity
9. electrical conductivity
10. flame coloration
11. oxidation state
12. formation of ionic compounds
13. water solubility of alkali metals

Example of atomic radius of alkali metals

Li-152 pm
Na-190 pm
K-227 pm
Rb-248 pm
Cs-265 pm

Melting point example of alkali metals

Li(180.5)
Na(97.8)
K(63.7)
Rb(38.9)
Cs(28.7)

Ionization energy example of alkali metals

Li-520.3 kJ/mol
Na-495.8 kJ/mol
K-418.9 kJ/mol
Rb-403 kJ/mol
Cs-375.7 kJ/mol

Chemical properties of alkali metals

1. Reactivity
2. Formation of oxides
3. formation of hydroxides
4. formation of hydrides
5. formation of halides
6. formation of nitrogen
7. reaction with acids
8. action of liquid ammonia
9. action of mercury- formation of amalgams

Important compounds of lithium

Lithium fluoride
Lithium chloride
Lithium nitride
Lithium carbonate
Lithium- aluminum hydride

Important compounds of sodium

sodium peroxide
sodium hydroxide/ caustic soda
anhydrous sodium carbonate/soda ash
hydrated sodium carbonate/washing soda
sodium bicarbonate
sodium chloride/common salt
sodium hypochlorite
sodium nitrite
sodium cyanide
sodamide

Important compounds of potassium

potassium hydroxide/caustic potash
potassium chloride
potassium bromide
potassium iodide
potassium cyanide

Uses and application of lithium

-lithium carbonate and lithium citrate in treatment of hypomanic and manic states
- lithium hydrogen carbonate is used to treat gout

Uses and application of sodium

-principal cation for extracellular fluid
-compounds used in pharmacy and medicine
Compounds:
-sodium acetate
-sodium bicarbonate
-sodium bisulfite
-sodium borate
-sodium chloride

Uses and application of potassium

-Potassium acetate
-potassium bitartrate
-potassium chloride
-potassium citrate

What is largely responsible for the chemistry of alkali metals?

The solitary electron in the outermost shell can be easily removed from the atom and it is the factor that is largely responsible for the chemistry alkali metals.

Electronegativity example of alkali metals

Li-1
Na-0.9
K-0.8
Rb-0.8
Cs-0.7

Color of lithium

crimson red

color of sodium

golden yellow

color of potassium

violet

color of rubidium

red

color or cesium

blue

Explain physical state of alkali metals

Except for Li, the alkali metals are extremely soft and readily fused. They are highly malleable and ductile. When freshly cut, they have a bright shine which is quickly tarnished as soon as metal comes in contact with atmosphere. Lithium is the hardest alkali metal and they become softer as you go down the group.

Explain atomic volume, atomic and ionic radii of alkali metals

As we move from lithium to caesium, an extra shell of electrons is added to each element. The addition of an extra shell increases the atomic volume. So, there is an increase of atomic and ionic radii (of M+ ions) as we move from lithium to caesium

Explain density of alkali metals

Li, Na and K are lighter than water. The densities increase with increase in atomic no. from Li to Cs.

Explain melting and boiling points of alkali metals

The melting and boiling points are very low due to the presence of weak interatomic bonds of the alkali metals. The melting and boiling points of alkali metals decrease when we move from Li to Cs.

Explain ionization energies of alkali metals

As alkali metals have only one electron in their outermost shell (ns1 electron), it can be removed very easily due to weak bond with nucleus. So, alkali metals have low ionisation energies. As the distance of ns1 electron from nucleus increases on moving from Li to Cs, its removal becomes more and more easy as we move from Li to Cs (decrease in ionisation energy).

Explain electropositive character of alkali metals

The elements which have a strong tendency to lose their outermost electrons to form the cations are said to be electropositive or metallic elements. In alkali metals the ns1 electrons are weekly bound with the nucleus and hence can be easily removed from the atom to form M+ cation.
Thus, these metals have a strong tendency to lose their ns1 electrons to form M+ cation and hence show strong electropositive / metallic character.
Because of the successive increase in the distance of ns1 electron from nucleus while we move from Li to Cs, the tendency of atoms to lose ns1 electron goes on increasing from Li to Cs. So, metallic character increases from Li to Cs.

Explain electronegativity of alkali metals

The alkali metals have a strong tendency to lose their ns1 electron and hence have a strong electropositive character. So, they have very little electronegative character. In other words, they have low values of electronegativity meaning they have little tendency to attract electrons towards themselves

explain coloration to the flame of alkali metals

Alkali metal impart distinctive color to flame.
Li --- Crimson red,

Na --- Golden yellow,

K --- Violet,

Rb --- Red,

Cs --- Blue.

Explain oxidation state of alkali metals

All the alkali metals show +1 oxidation state

Explain formation of ionic compounds of alkali metals

Alkali metals form ionic compounds with highly electronegative elements.

Explain water solubility of alkali metals

Virtually all salts of alkali metals are water soluble. They are more soluble than the salts of any other periodic group.

Explain reactivity of alkali metals

The reactivity of these metals increase with increase in atomic number. As there is a steady decrease in ionisation energies, Li reacts slowly with H2O; Na reacts vigorously; K, Rb and Cs react with increasing violence

explain formation of oxides of alkali metals

Alkali metals react with O2, or air rapidly and thus get rusted due to formation of their oxide on the surface of the metals. Due to this reason, alkali metals are stored in kerosene or paraffin oil.
Li when burnt in O2 gives mainly lithium monoxide (Li2O).
Na when burnt in O2 to form sodium oxide (Na2O) or sodium peroxide (Na2O2)
Other alkali metals react with O2 to form super oxide of MO2 type.
Normal oxides (O2-) react with H2O to form hydroxides by proton exchange.
On the other hand, the peroxides and super oxides are also strong oxidising agents and react with H2O to give H2O2 and O2 along with the metal hydroxides.

Explain formation of hydroxides of alkali metals

Hydroxides of alkali metals can be prepared by treating the normal oxides or the metals with H2O.
Since the electropositive character of the metals increases from Li to Cs the basic character of their hydroxides increases from LiOH to CsOH.

Explain formation of hydrides of alkali metals

All the alkali metals react with hydrogen directly at a temperature of 300 to 6000C and form the corresponding hydrides. The general reaction of alkali metals with hydrogen can be represented as follows:
2M+H2→2MH

explain reaction with nitrogen of alkali metals

Only Li reacts readily with N2 at room temperature to form lithium nitride (Li3N), which decomposes in water to form ammonia and lithium hydroxide.
6Li + N2 → 2Li3N
Li3N + 3H2O → 3LiOH + NH3
Other alkali metals also give the reaction on heating.

explain reaction with acids of alkali metals

Alkali metals react violently with dilute acids.

explain reaction with liquid ammonia of alkali metals

Alkali metals dissolve in liquid ammonia to form a blue solution (without the evolution of H2 gas). But in presence of catalytic amounts of oxidizing agents (e.g., as impurity), ammonia will rapidly react with the metals to form alkali amides (e.g., NaNH2)

Explain action of mercury of alkali metals

alkali metals dissolve readily in mercury and form amalgams.