Chemical Properties of Metals
Metals are electropositive elements because they have a tendency to lose one or more electrons, forming positive ions. Thus,
Na Na+ + eā
K K+ + e
Metals are capable of undergoing certain characteristic chemical reactions because of the electro positive character.
Reactions of Metals with Oxygen
Almost all metals react with oxygen to form metal oxides. The metals lose electrons which are gained by oxygen. For example, sodium forms sodium oxide, magnesium forms magnesium oxide, copper forms copper (II) oxide and iron forms iron oxide.
Metal oxides are basic in nature. Some of the metal oxides react with water to form alkalis.
Some metals react with oxygen vigorously while others do so only when heated together. Metals like sodium and potassium react vigorously with oxygen. They catch fire even when kept in air forming oxides. Since potassium and sodium metals react with oxygen even at room temperature they are reactive metals. Magnesium is less reactive than sodium or potassium. It has to be heated before it can combine with oxygen.
Take a piece of magnesium ribbon. Burn it using a matchstick and introduce it into a gas jar. The piece continues to burn with a dazzling light until all the oxygen (in the air) inside the jar is consumed. A white powder of magnesium oxide is obtained in the process.
The metals, iron and copper too react with oxygen only when they are heated for a long time. Metal oxides produced in the process are basic in nature. Some of these dissolve in water, forming alkalis. Thus,
Reaction with Dilute Acids
Many metals react with dilute hydrochloric acid to give metal chlorides and hydrogen. But some metals like copper, silver, gold, platinum, etc., do not react with dilute HCl.
The active metal sodium, reacts with dilute hydrochloric acid to form sodium chloride and hydrogen.
The active metal magnesium, reacts with dilute hydrochloric acid to form magnesium chloride and hydrogen.
Zinc is less active in comparison to sodium and magnesium. Chemically pure zinc is attacked very slowly by dilute hydrochloric acid, but impure zinc reacts, liberating hydrogen.
Lead is less active. Dilute hydrochloric acid has little effect on the metal.
Reaction with WaterSome metals react with water while others do not. The reactivity with water differs from metal to metal.
Sodium and potassium are very reactive metals. They react violently with water forming alkalis (sodium hydroxide or potassium hydroxide) and hydrogen.
Calcium also reacts with water forming calcium hydroxide (alkali) and hydrogen.
Magnesium is not as reactive as potassium and calcium. It does not react with cold water, but reacts with boiling water to form magnesium oxide and hydrogen.
The activity of zinc is less than that of potassium or calcium. It does not react with cold water, but reacts with boiling water to form zinc oxide and hydrogen.
Iron is less active than potassium, calcium and magnesium. It reacts with steam to form the magnetic oxide of iron, Fe3O4.
Reaction with Hydrogen
Most of the metals do not combine with hydrogen. Only active metals like sodium, calcium and magnesium react with hydrogen to form metal hydrides.
Reaction with Chlorine
Metals react with chlorine to form ionic chlorides. Metals form ionic chlorides because they can give electrons to chlorine atoms to form ions. However the order of reactivity differs from metal to metal.