Alkali Metals Reactions | Reactivity | Group IA Elements

Electron Configuration of alkali metals

Those elements have only one electron in their last shell. Commonly, we can show it as 1s² 2s²2p⁶.. ns¹

Example:
Na - 1s² 2s²2p⁶ 3s¹
K - 1s² 2s²2p⁶ 3s²3p⁶ 4s¹

Reactions of alkali metals

Alkali metals are very reactive due to existence of only one electron in their last shell. Lot of compounds of these alkali metal's are soluble in water. Most solids of alkali metal compounds take white colour.

Reactivity of alkali metals change down the group

Observe the reaction of lithium, sodium and potassium reaction with water. You can clearly see a difference of reactions. Potassium reacts vigorously with water and lithium slowly reacts.

When going down the group, atomic radius of metal increases. To have very good reactivity for metals, ease of eliminating electrons should be high (electrons should be removed easily). When atomic radius increases, elimination of last shell electrons gets more easier. So going down the group, reactivity increases.

• Reactivity of sodium is higher than lithium.
• Reactivity of potassium is higher than sodium.

Water and alkali metals reactions

Alkali metals react with water and emit hydrogen and relevant metal hydroxide are given. These metal hydroxides are strong bases and dissolve very well in water.

Reaction of potassium with water is a highly flammable.

2Na + 2H₂O = 2NaOH + H₂

Solid sodium metal reacts with water to produce aqueous sodium hydroxide and hydrogen gas.

Acids and alkali metals reaction

Alkali metals react with strong acids (HCl , HNO₃ , H₂SO₄) and emit hydrogen gas and produce relevant alkali metal salt.

2Na + 2HCl = 2NaCl + H₂

2K + H₂SO₄ = K₂SO₄ + H₂

Hydrogen and alkali metals reaction

Metal hydrides (H^-) are given as products.

2Na + H₂ = 2NaH

Those ionic hydrides have H^- ions. 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 hydrogen gas.

Alkali metal hydrides with proton donors

Reactions of air and alkali metals

Liquid Li reacts (burning) with oxygen gas and make lithium oxide.

Sodium, potassium react with Oxygen and make relevant Oxide of metal.

4Na + O₂ = 2Na₂O

4K + O₂ = 2K₂O

When sodium, potassium and other alkali metals at below periods is heated in a hot air stream, alkali metal peroxides are formed.

2Na + O₂ = Na₂O₂

2K + O₂ = K₂O₂

Also potassium, rubidium can make super oxides. Alkali metal superoxides are colourful.

Rb + O₂ = RbO₂

Reaction of water with alkali metal oxides

Above metal oxides can react with water and make metal hydroxides.

Na₂O + H₂O = 2NaOH

K₂O + H₂O = 2KOH

Halogen and alkali metals

group IA elements react with halogen and form alkali metal halides. Sodium chloride, potassium bromide are some examples to alkali metal halides.

2Na + Cl₂ = 2NaCl

Nitrogen and alkali metals

Only lithium reacts with nitrogen gas and forms lithium nitride (Li₃N) which is a red solid.

6Li + N₂ = 2Li₃N

Li₃N reacts with water and and produce ammonia gas and lithium hydroxide.

Li₃N + 3H₂O = 3LiOH + NH₃

Sulfur and alkali metals

Sodium reacts sulfur form metal sulfide when heat is supplied.

2Na + S = Na₂S

Those sulfides can react with dilute acids. And hydrogen sulfide gas is released.

class="reaction-equations"Na₂S + HCl = 2NaCl + H₂S

Ammonia and group IA metals

Sodium reacts with ammonia to produce hydrogen gas and NaNH₂. In this reaction ammonia behave as an acid.

2Na + NH₃ = NaNH₂ + H₂

Reaction with phosphorus and alkali metals

Sodium reacts with phosphorous in the presence of heat and produce sodium phosphide.

3Na + P = Na₃P

Reaction of hydrogen sulfide and group IA metals

Sodium reacts with hydrogen sulfide (H₂S) to give metal sulfide and H₂ gas. Due to release of hydrogen gas, hydrogen sulfide is an acidic gas.

2Na + H₂S = Na₂S + H₂

Alkali metal halides

The alkali metal halides have high melting points and they are 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)

Stability of alkali metal halides

Fluorides of alkali metals are most stable while iodides of alkali metals are least stable.

Melting and boiling points of alkali metal halides

Melting and boiling points of alkali metal halides decreases with the increase in atomic mass of the halides as:

F^- > Cl^- > Br^- > I^-

As an example, melting point of NaCl is higher than NaBr.

For given halide ion, melting and boiling points of LiX is always less than NaX.

Solubility of alkali metal halides

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.

Salts of oxo acids

Alkali metals are electropositive metals. Therefore they form salts with oxo acids.

What are the 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 and bicarbonates of alkali metals

Carbonates of alkali metals are stable to heat (except lithium carbonate). 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 earth metal carbonates. Lithium carbonate and alkali earth metal carbonates decompose to metaal oxide and carbon dioxide gas when heat is given.

Bicarbonates of alkali metals (except Llithium bicarbonate) decomposes into the carbonates, carbon dioxide and water.

Colours of super oxides of alkali metals

Alkali metal	Alkali metal super oxide	Colour
Potassium	KO2	Orange
Potassium	RbO2	Brown
Potassium	KO2	Dark Orange

Why LiCl is soluble in organic solvents?

Li⁺ has very high polarizing power. Therefore LiCl is covalent in nature. Being covalent in nature, it is soluble in organic solvents.

Why potassium is much reactive than sodium?

Both potassium and sodium are alkali metals and form +1 ions. Sodium is located at third period and potassium is located at fourth period in the periodic table. So radius of potassium is higher than sodium. When radius is higher, eliminating an electron is much easy.

So, potassium can eliminate its last shell electron more easily than sodium atom. So potassium reacts so fast than sodium and reactivity of potassium much higher than sodium.

What are the factors of anomalous behavior of lithium?

• Small size of atom and ion
• high ionization enthalpy
• absence of d- orbitals in its valence shell

What are the precipitates formed by alkali metals?

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.

Why sodium should kept under kerosene oil?

Due to higher reactivity, we cannot store sodium outside environment (in air) or water. Sodium can react with oxygen, water.

Kerosene is not reactive liquid. So sodium does not react with kerozene. Therefore we can store sodium metal in kerozene oil.

why are alkali metals not found in nature

Alkali metals are very reactive. SO they readily react with water, oxygen which are common constituents in the environment. So we cannot find alkali metals as pure metals.

Biological importance of sodium and potassium

• Sodium and potassium are most common cations in biological systems.
• Though Na⁺ and K⁺ ions are quite similar chemically but surprisingly they differ greatly in their biological activities.
• Their distribution in biological systems is also different. A typical man weighing 70Kg contains about 90g of sodium and 170g of potassium as compared with only 5g of iron and 0.06g of copper.
• The most salient feature is that K+ ions are present in higher concentrations inside the cells than Na⁺ ions while their relative concentrations are reverse outside the cells.
• In other words, K⁺ ions are concentrated inside the cells while Na⁺ ions are concentrated outside the cells.
• Na⁺ ions are primarily found in blood plasma and in the interstitial fluid which surrounds the cells.
• On the other hand, K⁺ ions are most abundant cations within cell fluids. There is very considerable variation in the concentration of Na⁺ and K⁺ ions found on the opposite sides of cell membranes. For example, in blood plasma, Na⁺ ions are present to the extent of 143m .

Written by : Heshan Nipuna
Last Edition : 27/09/2019

Questions

Why do the alkali metals form many precipitates?

Alkali metals >do not form many precipitates like alkali earth metals and d block metals.

When you study solubility of inorganic compounds, you may see, a lot of alkali metals are soluble in water.

Take few examples to explain this.

• Metal hydroxides solubility: All alkali metal hyydroxides are soluble in the water. But from alkaline earth metals, only barium hydroxide is soluble in water. Also all 3d metal hydroxides are precipitates.

Related Topics to s Block Group 1 Elements - Alkali Metals