Chemical Properties of Metals and Reactivity Series
Introduction:
A chemical element is a substance that cannot be broken down by chemical means. There are 118 known elements. An element can be classified into:
- Metals
- Non-metals
- Metalloid (possesses properties of both metal and non-metals)
What Are Chemical Properties?
Chemical properties are any of the properties of matter that can be observed and measured only by performing a chemical change or chemical reaction. Chemical properties cannot be determined by touching or viewing a sample; the structure of the sample must be altered for the chemical properties to become apparent.
Here are some examples of chemical properties:
- Reactivity with other chemicals
- Toxicity
- Coordination number
- Flammability
- Enthalpy of formation
- Heat of combustion
- Oxidation states
- Chemical stability
What Is a Metal?
Metals are substances that form naturally below the surface of the earth. Most metals are lustrous or shiny. Metals are inorganic, which means they are made of substances that were never alive. Metals are natural compounds of the earth’s crust, which are generally found in the form of metal ores, associated both with each other and with many other elements. They are also naturally present in the rocks washed by surface water and groundwater and in atmospheric dust.
Chemical Properties of Metals:
Reaction with Air:
Metals can burn in air, react, or don’t react with air.
Metal + oxygen → Metal Oxide
Some metals like Na and K are kept immersed in kerosene oil as they react vigorously with air and catch fire.
Some metals like Mg, Al, Zn, and Pb react slowly with air and form a protective layer.
Mg can also burn in the air with a white dazzling light to form its oxide.
Fe and Cu don’t burn in the air but combine with oxygen to form oxide. When heated, iron filings burn when sprinkled over the flame.
Metals like silver, platinum, and gold don’t burn or react with air.
2Na + O2 → Na2O
2Mg + O2→ 2MgO
2Cu + O2→ 2CuO
4Al + 302 → 2Al2O3
Amphoteric Oxides: Metal oxides that react with both acids as well as bases to form salt and water, e.g., Al2O3, ZnO.
Al2O3+ HCl→ AlCl3+ H2O
Al2O3+ NaOH → NaAlO2+ H2O
(Sodium
aluminate)
Reaction with Water:
When a metal reacts with water, it forms metal hydroxide. Hydrogen gas is also produced in this reaction. Following is the general equation for this reaction.
Metal + Water ⇨ Metal hydroxide + Hydrogen
Different metals react with water at different rates. Most metals do not react with water. However, alkali metals react vigorously with water.
The Reaction of Sodium and Potassium with Water:
The reaction between sodium and water is highly vigorous. When sodium reacts with water, sodium hydroxide, and hydrogen are produced. This reaction is highly exothermic. So much heat evolves during the reaction that the reaction mixture catches fire. The same is the case for potassium. The following equation shows this reaction.
Na + H2O ⇨ NaOH + H2
K + H2O ⇨ KOH + H2
As sodium and potassium are highly reactive, it is kept stored under kerosene so that they do not get a chance to react with moisture that may be present in the air. This is done in order to prevent any accidental fire.
The Reaction of Calcium with Water
When calcium reacts with water, calcium hydroxide, and hydrogen gas are formed. This too is an exothermic reaction. When bubbles of hydrogen gas stick to metal then calcium starts floating. The following equation shows this reaction.
Ca + 2H2O ⇨ Ca (OH)2 + H2
The Reaction of Magnesium with Water:
Magnesium does not react with cold water. It reacts with hot water and forms magnesium hydroxide and hydrogen gas. Magnesium starts floating due to hydrogen bubbles sticking to the metal. The following equation shows this reaction.
Mg + 2H2O ⇨ Mg (OH)2 + H2
When steam is passed over magnesium, the reaction becomes fast. Magnesium oxide and hydrogen gas are formed in this reaction.
Mg + H2O ⇨ MgO + H2
The Reaction of Aluminum with Water:
Aluminium does not react with cold or hot water. But when steam is passed over aluminum, aluminum oxide, and hydrogen gas are produced. The following equation shows this reaction.
2Al + 3H2O ⇨ Al2O3 + 2H2
The Reaction of Iron with Water:
The reaction between iron and cold water is too slow to be noticed. When iron reacts with atmospheric moisture, it forms rust (iron oxide). But this is a very slow reaction.
When steam is passed over iron, iron oxide, and hydrogen gas are formed. The following equation shows this.
3Fe + 4H2O ⇨ Fe3O4 + 4H2
Lead, copper, silver, and gold do not react with water at any temperature.
Reaction of Metals with Acids:
Metal + dilute acid → Salt + Hydrogen gas
Metals react with dilute hydrochloric acid and dilute sulphuric acid to form
salt and hydrogen gas.
Fe + 2HCl → FeCl2+ H2
Mg + 2HCl → MgCl2+ H2
Zn + 2HCl → ZnCl2+ H2
2Al + 6HCl → 2AlCl3+ 3H2
Copper, mercury, and silver don’t react with dilute acids.
Hydrogen gas produced is oxidized to water when metals react with nitric acid. But Mg and Mn react with very dilute nitric acid to evolve hydrogen gas.
Mg + 2HNO3→ Mg(NO3)2+ H2
Reaction of Metals with Other Metal Salts:
Metal A+ Salt sol. of metal B à Salt sol. of metal A+ metal B
All metals are not equally reactive. Reactive metals can displace less reactive metals from their compounds in solution. This forms the basis of the reactivity series of metals.
The reactivity series is a list of metals arranged in order of their decreasing activities.
Fe + CuSO4→ FeSO4+ Cu
Zn + CuSO4→ ZnSO4+ Cu
Most reactive metal reacts vigorously while the least reactive metal do not react with normal condition. For example, potassium (K) is kept at the top of the list followed by sodium (Na), calcium (Ca), Magnesium (Mg), and so on. Gold, silver, mercury, and copper are kept in the bottom; these metals do not react in normal conditions and hence are called noble metals. This is one of the reasons that gold and silver metals are used in making jewelry.
Summary
- A metal is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well.
- Metals are malleable, ductile, sonorous, lustre, and good conductors of electricity and heat.
- A nonmetal is simply an element that does not display the properties of a metal.
- Non-metals are non-malleable, non-ductile, non-sonorous, non-lustre, and bad conductors of electricity and heat.
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