Important alkali and alkaline earth metals, inertness of noble metals, Importance of silver, gold and platinum

Important alkali and alkaline earth metals, inertness of noble metals, Importance of silver, gold and platinum

Important alkali and alkaline earth metals

The most important alkali metal is sodium.

Sodium is soft metal and can be cut with a knife.

It's melting point is 97.8 oC and boiling point is 881.4 oc.

It is a silvery white metal.

It is extremely reactive metal.

It reacts with water violently to form sodium hydroxide.

I.e., 2Na + H2O --'--------> 2NaOH + H2

In limited supply of oxygen, sodium burns to produce sodium oxide. But in excess of oxygen, it forms pale yellow sodium peroxide (Na2O2).

Na + O2 -------- > 2Na2O2

Question: Why sodium is soft and can be cut with a knife while iron is hard and strong, although both are metals?

Answer. Iron is hard and strong because:

i. In iron metal, atoms are tightly packed due to small size.

ii. Iron atoms are held together through strong metallic bonds due to many electrons in valence shell

While Na is soft because

I. In sodium metal, atoms are not tightly packed due bigger atoms

ii. Na atoms are held together through weak metallic bonds due to only one valence electron.

Question: Why should sodium not be hold with fingers?

Answer

This is because sodium metal reacts with water (moisture) in fingers violently to produce NaOH sodium hydrogen gas. This reaction is highly exothermic and resuls in light explosion. For this reason, it should not be picked with fingers.

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