Materials: Metals and Non-metals

 Materials: Metals and Non-metals

Element:

•   A substance which cannot be broken down into two or more simpler substances by chemical reactions ( by applying heat, light or electricity) is called an element.

•    For example, iron is an element because it cannot be broken down into two or more simpler substances by carrying out chemical reactions such as by applying heat, light or electricity.

•  All elements themselves are the simplest substances. 

Some common elements are:

•   Hydrogen, Helium, Carbon, Nitrogen, oxygen, Sulphur, Phosphorus, Silicon, Chlorine, Bromine, Iodine, Sodium, Potassium, Magnesium, Calcium, Aluminium, Iron, Zinc, Copper, Silver, Gold, Mercury etc,.

•    Every element is represented by a ‘symbol’. A symbol is the short way to write an element. All the elements have separate symbols. No two elements can have the same symbol.

For example, the symbol of Hydrogen is H whereas the symbol of nitrogen is N.

•       The symbol of an element also represents ‘one atom’ of that element.

Atom:

•       The smallest particle of an element is called ‘atom’. A sample of an

element contains only one kind of atoms.

•       An element is a substance which is made up of only one kind of atoms. For example, Nitrogen element is made up of only nitrogen atoms whereas iron element is made up of only iron atoms.

•       The atoms of an element remain unaffected by the physical changes in the element. For example, atoms of liquid sulphur or vapour forms of sulphur would be the same as that of solid sulphur.

•       Although there is an enormous variety of substances in the universe but the number of elements forming these substances is limited.

•       118 elements are discovered but there are only 92 naturally occurring elements.

An important classification of elements is in terms of metals and non- metals.

Metals and non-metals show different physical properties. The important physical properties of them are :

 

 1.   Malleability- The property with which metals can be beaten into thin sheets is called malleability.

•  Most of the metals are malleable. Gold and Silver are the best malleable metals. Aluminium and Copper are also highly malleable metals.

•     For example, aluminium metal can be hammered to form thin aluminium foils. It is because of the property of malleability of iron, ironsmith can change the shape of a block of iron metal by hammering to make different iron objects such as an axe, a spade or a shovel, etc.

•    Non-metals are not malleable. They are brittle. This means that non- metals cannot be beaten into thin sheets with a hammer. They break into small pieces when hammered.

•       Carbon is a non-metal. Carbon is found in many forms such as charcoal, coke, graphite ,etc. Coal is also mainly carbon.

•       Pencil lead is a form of carbon called graphite. If we take a pencil lead and beat it with a hammer, it will break into pieces.

Ductility:

     •    Generally, metals are ductile.

     •    The property by which metals can be drawn into wires is called ductility.

     •     Most of the metals are ductile. Gold and Silver are among the best ductile metals. Copper and aluminium metals are also very ductile and can be drawn into thin copper wires and aluminium wires ( which are used as electric wires.

    •       Non –metals are not ductile. This means that non-metals cannot be drawn into wires. They are easily snapped on stretching.

 Sonorous:

•       Metals are sonorous. This means that metals make ringing sound when we strike them.

•       If we drop a metal coin or a metal utensil on the floor of our house, we hear a ringing sound.

•       When the hammer of an electric bell strikes the metal gong, even then a ringing sound is produced.

•       Non-metals are not sonorous. This means that solid non-metals do not make a ringing sound when we strike them.

•       For example, if we drop a piece of carbon (Charcoal) or a lump of sulphur on the floor or strike them with a hammer , we do not hear any ringing sound.

Conductance:

•       Metals are good conductors of heat and electricity. This means that metals allow heat and electricity to pass through them easily.

•       For example, copper, silver, gold, aluminium and iron are good conductors of heat.

•       Though all the metals are good conductors of heat, Silver metal is the best conductor of heat. Copper metal is a better conductor of heat than aluminium metal.

•       Cooking utensils are made of metals because being good conductors of heat, they transfer the heat of gas stove quickly from the bottom of utensil to the food kept inside it.

•       Electric wires are made of metals because they allow electricity to pass through them easily.

•       For example, copper wires are used in house hold electric wiring since it is a better conductor of electricity than aluminium.

•       Silver metal is the best conductor of electricity.

•       Non-metals are poor conductors of heat and electricity. This means that non-metals do not allow heat and electricity to pass through them.

•       For example, carbon and sulphur are non-metals. They do not conduct heat and electricity.

     •       Many of the non-metals are, infact, very good insulators.

     •       There are, however, some exceptions. A form of carbon element, graphite is a non-metal which is a good conductor of electricity.

Lustre:

    •       Metals are lustrous. This means that metals have a shiny appearance.

     •       If we observe the freshly cut surface of metals, we will find that they have a shiny appearance. This is called metallic lustre.

•       The shiny appearance of metals make them useful in making jewellery and decoration pieces.

•       For example, gold and silver are used for making jewellery because they are bright and shiny.

     •       Non-metals are not lustrous. They are dull in appearance.

     •       For example, solid non-metals like sulphur and phosphorous donot have lustre. They are dull in appearance.

     •       However, there is one exception. Iodine is a non-metal having lustre.

Hardness:

•       Metals are generally hard. This means that most of the metals cannot be cut easily.

•       There are , however, some exceptions to this property of hardness of metals.

•       For example, Sodium and Potassium are soft and can be cut with a knife easily.

•       Most of the solid non-metals are quite soft. This means that they can be cut easily.

•       Solid non-metals like sulphur and phosphorous are soft non-metals which can be easily cut into pieces.

•    Diamond, a form of solid non-metal, carbon, is very hard. In fact, diamond is the hardest natural substance known.

     •       Mercury is the metals that exists in liquid state at room temperature.

     •     Bromine is the non-metal that exists in liquid state at room temperature.

 Metals and non-metals show different chemical properties. Some of the important chemical properties of them are :

 1.     Reaction with oxygen:

•    Metals react with oxygen to form metal oxides. Metal oxides are basic in nature.

      Metal + Oxygen → Metal oxide

•  When magnesium burns in air, it combines with oxygen of air to form magnesium oxide ( basic oxide). The basic metal oxides turn red litmus to blue.

    Magnesium + oxygen → Magnesium oxide

•  Magnesium oxide dissolves in water to form magnesium hydroxide solution 

   Magnesium oxide + Water →    Magnesium hydroxide

•  Reaction of iron metal with oxygen of air in nature

•       During the rusting of iron, iron metal combines slowly with the oxygen of air in the presence of water ( moisture) to form a compound called ‘iron oxide’. This iron oxide is called rust.

   Iron +  Oxygen + water       → Iron oxide

•   Reaction of copper metal with moist air in nature

     When a copper object is exposed to moist air for a long time, then copper reacts with water, carbon dioxide and oxygen present in the moist air to form a green coating on the copper object.

The green coating is a mixture of copper hydroxide and copper carbonate

•    Sodium and Potassium are highly reactive metals with oxygen and water. If they are kept exposed to air, they will react with atmospheric oxygen vigorously. They quickly react with water also. In order to prevent their reaction with atmospheric oxygen and moisture, they are always store under kerosene.

Reaction of a non-metal with oxygen

Non-metals react with oxygen to form non-metal oxides. Non-metal oxides are acidic in nature.

Non-metal    + Oxygen     →     Non-metal oxide

•       The acidic non- metal oxides turn blue litmus to red

 •       When sulphur burns in air, it combines with oxygen of air to form sulphur dioxide (acidic oxide)

     Sulphur + Oxygen      → Sulphur dioxide

Sulphur dioxide dissolves in water to form sulphurous acid solution.

     Sulphur dioxide +     water        → Sulphurous  acid 

Sulphurous acid turns blue litmus to red showing that it is an acid.

 2. Reaction with water

•       When a metal reacts with water, then a metal hydroxide and hydrogen gas are formed.

Metal + Water      →  Metal hydroxide + Hydrogen

The vigour (intensity) of reaction of a metal with water depends on its chemical reactivity.

•   Some metals react vigorously even with cold water. Ex. Sodium

•   Some metals react with hot water. Ex. Magnesium 

•    Some metals react with steam. Ex. Zinc and Iron      

•      Some metals don’t react with water and steam. Ex. Copper, Silver, Gold

  •  Non-metals do not react with water.

Phosphorous is a very reactive non-metal. If phosphorous is kept open in air, it reacts with the oxygen of air and catches fire. So, in order to protect phosphorous from atmospheric air, it is stored in water.

3.  Reaction with acids

•       Most of the metals react with dilute acids to form salt and hydrogen gas. 

   Metal +  Acid    →     Salt       + Hydrogen

   Depending on their reactivity, some metals react vigorously with dilute acids, some metals react rapidly and some metals react with dilute acids only on heating whereas some metals do not react with dilute acids at all.

Ex. 

    Magnesium + Hydrochloric acid    → Magnesium chloride + Hydrogen

  Hydrogen gas burns with a ‘pop’ sound when a lighted match stick is brought

near the mouth of a test- tube.

The less reactive metals like copper, silver and gold do not react with dilute acids.

•       Copper metal does not react with dilute sulphuric acid to produce hydrogen gas. However, it reacts with hot and concentrated sulphuric acid but no hydrogen gas is produced.

•       Certain food stuffs like citrus fruit juices ( orange juice), pickles, chutney and curd, etc., contain acids. When they are kept in iron, aluminium or copper containers, the acids present in them react with the metal of container slowly to form toxic salts. These toxic salts can make us sick and damage our health.

•       Non-metals do not react with dilute acids to form salts and hydrogen gas.

2. Reaction with bases

  •  All metals do not react with bases like sodium hydroxide. Some metals react with bases to form salts and hydrogen gas.

     Metal  + Base  →   Salt + Hydrogen

 •   Aluminium is a metal. Sodium hydroxide is a base. When aluminium is heated with sodium hydroxide solution, Sodium aluminate (salt) and hydrogen gas are formed.

Aluminium + Sodium hydroxide →        Sodium aluminate + Hydrogen

•   Zinc metal also reacts with sodium hydroxide solution to form salt and hydrogen gas.

  Zinc + Sodium hydroxide             →    Sodium zincate + Hydrogen

 The reactions of non-metals with bases are complex.

Reactivity series of metals

•       Some metals are very reactive whereas other metals are less reactive or unreactive.

•       Reactivity series of metals is the descending order of metals with their reactivities.

•       In the reactivity series, the most reactive metal is placed at the top and the least reactive metal is placed at the bottom.

Displacement reaction

•       A chemical reaction in which a more reactive metal displaces a less reactive metal from its salt solution is called displacement reaction.

 Ex. 1    Adding iron nails to copper sulphate solution.

Since iron is a more reactive metal than copper, iron displaces copper from its salt solution i.e copper sulphtate solution(blue). As a result iron sulphate solution (green) and copper (brown) are formed. Copper can be seen as a brown colored deposit on iron nails.

     Iron + Copper sulphate      → Iron sulphate + Copper

 Ex.2

If we add few copper metal turnings to iron sulphate solution, no displacement reaction takes place because copper is a less reactive metal than iron. So, copper can not displace iron from it’s salt solution (iron sulphate solution).

   Copper +    Iron sulphate     → No displacement reaction

Ex.3

If we add one or two zinc metal granules to Copper sulphate solution (blue) the blue colour gradually disappears and solution becomes colourless due to the formation of zinc sulphate solution. The brown copper is deposited on zinc ganules.

     Zinc  +  Copper sulphate  →            Zinc sulphate +            Copper

Zinc is a more reactive metal than copper. So, in this reaction zinc displaced Copper from its salt solution i.e Copper sulphate solution.

 Ex.4

If we place a strip of copper metal in zinc sulphate solution, then no displacement reaction will take place.

Copper +    Zinc sulphate → No displacement reactio

Ex 5.

 When a zinc metal granule is added to iron sulphate solution, then displacement reaction will take place to form zinc sulphate and iron.

Zinc     + Iron sulphate → Zinc sulphate + iron 

Ex.6

If we place an iron nail in zinc sulphate solution, then no displacement reaction will take place because iron is less reactive than zinc.

Iron     +    Zinc sulphate   →      No displacement reaction

Uses of metals

•  Metals like iron, copper and aluminium are used to make cooking utensils and water boilers.

•   Copper metal is used in making electrical wires and electric appliances.

•  Aluminium metal is used for making electric cables. It is also used to make aeroplanes. 

•  Iron metal is used to make nails, screws, machines, railway lines, vehicles such as buses, cars and agricultural tools like plough, hoe etc.

 •  Zinc metal is used for galvanizing iron to prevent rusting.

 •  Some metals like gold and silver are used in making jewellery.

•  Mercury metal is used in making thermometers.

Uses of non-metals

Ø Oxygen is a non-metal . It is used by all living organisms for breathing.

     • Nitrogen is a non-metal. It is used in making fertilisers to improve the growth of plants.

     •  Chorine is non-metal. It is used to kill the germs present in water.

      • Iodine is a none-metal. It is used to make a purple coloured solution called Tincture iodine. It is applied on wounds as an antiseptic.

      •  Sulphur and Phosphorus are used fireworks(crackers).

      •  Carbon is a non-metal. It is used in the form of graphite, to make pencil leads and electrodes

 Metalloids

The elements which possess the properties of both metals and non- metals are called metalloids.

Ex. Silicon, Germanium, Arsenic etc.