Metals And Non-metals

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

Metals act as reducing agents because highly reactive metals have the ability to displace low reactivity metals from their compounds. Non-metals do not display this property.

(a) Metals form oxides (metallic oxides) which are basic in nature. Some examples are Na₂O, K₂O etc.

(b) Non-metals form oxides (non-metallic oxides) which are acidic in nature. Some non-metallic oxides are NO₂, SO_2.

Iodine and carbon are non-metals which are lustrous. Note that carbon is lustrous only in certain forms like diamond, and graphite.

(a) Gallium and Caesium are two metals which have very low melting points. The melting point is so low that they start to melt if kept in our palms.

(b) Sodium and potassium are two metals which are soft and can be cut with a knife. They belong to the group of alkali metals. (Group 1 elements)

(a) Silver and copper are the best conductors of heat.

(b) Mercury and lead are two poor conductors of heat.

The property of metals which allow them to be beaten into thin sheets is called malleability. Gold and silver are the most malleable metals.

The ability of the metals to be drawn into thin wires is known as ductility. Gold and platinum are the most ductile metals.

(a) Sodium oxide (Na₂O), potassium oxide (K₂O) are metal oxides which are water soluble.

(b) Copper(II) oxide (Cu₂O), Beryllium oxide (BeO) are metal oxides which are water insoluble.

The process of coating an oxide layer over a metal is called anodizing. Usually, aluminium is selected as the metal, and the oxide coating will be aluminium oxide. Anodising is done to make the metal resistant to further corrosion.

The reactivity of the elements is determined by the tendency to have a completely filled valence shell. The electron dot structure of Na (sodium) and Cl (chlorine) atoms are shown in the figure below.

Electron dot structure of Na and Cl

To attain completely filled valence shell, Na has to lose the outermost electron, and Cl needs one electron to complete the valence shell.

By losing an electron, Na becomes Na⁺ (cation) and this electron is accepted by Cl to form Cl^- (anion). The oppositely charged ions attract each other and form NaCl. They are held together by strong electrostatic forces of attraction. The bond existing between them is called an ionic bond.

Figure 1: Formation of sodium chloride

Since the inter-ionic forces are very strong, it requires a considerably large amount of energy to break the bond. Hence, ionic compounds have high melting point.

The properties of metals and non-metals are given in the form of a table shown below. The properties mentioned here apply to the metals and non-metals generally. However, all metals and non-metals may not obey the given properties; there might be exceptions.

The process of heating a sulphide ore strongly in the presence of excess air is called roasting.

The process of heating a carbonate ore strongly in the presence of limited air is called calcination.

(a) An alloy is a homogenous mixture of two or more metals, mixed in a suitable proportion.

(b) Corrosion is the process of destruction of a material caused by chemical reactions between the material and the surrounding environment.

(a) Iron (II) oxide (FeO), as well as iron (III) oxide (Fe2O3), are oxides of iron. When iron reacts with steam, both oxides are formed and the product is in a combined form (FeO.Fe₂O₃ or Fe₃O₄).

3Fe(s) + 4H₂O(g) → Fe₃O₄(s) + 4H₂(g)

(b) Calcium and potassium are two highly reactive metals in the reactivity series.

Potassium reacts very violently with water, and hydrogen is released. The reaction is so exothermic that the evolved hydrogen catches fire immediately.

2K(s) + 2H₂O(l) → 2KOH(aq) + H₂(g) + heat energy

The reaction of calcium with water is not as violent as the above reaction. The heat evolved is not sufficient for the hydrogen to catch fire. Also, calcium starts floating because the bubbles of hydrogen gas formed stick to the surface of calcium.

Ca(s) + 2H₂O(l) → Ca(OH)₂(aq) + H₂(g)

(a) Magnesium loses two electrons to attain a noble gas configuration, whereas oxygen gains two electrons to completely fill the valence shell.

Mg → Mg²⁺ + 2e^‑

O + 2e^-→ O^2-

(b) Sodium loses one electron to have a completely filled valence shell, whereas oxygen gains two electrons to complete the valence shell.

Na → Na⁺ + e^‑

O + 2e^-→ O^2-

(a) Ionic compounds are made up of oppositely charged ions which are held together by strong electrostatic force of attraction. Due to this reason, they are hard solids. When large pressure is applied, they tend to break into pieces.

(b) Conduction of electricity is achieved by the movement of charged particles. In the molten state or in their aqueous solution form, ionic compounds contain ions which can move throughout the solution/molten solid, which helps in conducting electricity.

(a) Highly reactive metals (e.g., sodium, potassium) are reduced from their compounds by electrolytic reduction. By electrolyzing the chlorides or oxides of these metals, the pure metal is deposited at the cathode.

Electrolysis of molten sodium chloride

(b) Metals which come in the middle of the reactivity series are reduced from their compound using any of the following techniques.

i. If the compound is a metal oxide, then it is reduced to the corresponding metals by reduction using carbon (coke) in the presence of heat.

ii. If the compound is a metal carbonate, then it is converted into corresponding metal oxide by strongly heating it in the limited air (calcination). Later, metal oxides are reduced to metals using carbon.

iii. If the compound is a metal sulphide, then it is converted into corresponding metal oxide by strongly heating it in excess air (roasting). Then the metal oxide obtained is reduced to metal using carbon.

(a) Cinnabar (HgS – mercury(II) sulphide or mercuric sulphide) is an ore of mercury. It is heated in air to give mercuric oxide (HgO). Mercuric oxide is further heated to get mercury. The reactions involved are,

(b) Copper glance is a sulphide ore of copper (Cu₂S). So it is converted to cuprous oxide (Cu₂O) by just heating in air. Cuprous oxide is reduced to copper using carbon. The reactions involved are,

(a) When manganese dioxide (MnO₂) is heated with aluminium powder, displacement reaction takes place, and manganese is obtained as the product along with aluminium oxide. It is an exothermic reaction and hence Mn is obtained in molten form.

3MnO₂(s) + 4Al(s) → 3Mn(l) + 2Al₂O₃(s) + heat

(b) Iron (III) oxide is heated with aluminium powder to form iron and aluminium oxide. This is another example of a displacement reaction and is highly exothermic. This reaction is also known as thermit reaction.

Fe₂O₃(s) + 2Al(s) → 2Fe(l) + Al₂O₃(s) + Heat

For a metal in the middle of the reactivity series, having a sulphide ore, the following processes are done to extract the metal M.

i. The ore might contain impurities (also called gangue) which must be removed before the extraction of metal.

ii. The metal sulphide ore is subjected to strong heating in excess air. This process is called roasting, and it converts the metal sulphide to the corresponding metal oxide. The reaction can be represented as:

iii. Now, the metal oxide is reduced to the metal M using suitable reducing agents like C (coke) in the presence of heat.

iv. Once the extraction is complete, M is subjected to various refining processes to remove impurities from the metal.

A reactivity series is a list of metals which are arranged in the order of their decreasing activity. This means the metal at the top of the series is the most reactive and the metal at the bottom of the list is the least reactive metal.

To develop a reactivity series, take pieces of different metals (e.g., iron, copper, zinc etc) and the salt solutions of those metals (i.e., iron sulphate, copper sulphate, zinc sulphate etc).

Add a metal piece to a different metal salt solution. Check for any colour changes in the solution or to the metal piece and record your observations.

One can tell that for metals A and B if the following reaction occurs,

metal A + salt solution of B → metal B + salt solution of A

then, metal A is more reactive than B. Similarly by trying out various combinations of metals with metal salt solutions, one can create a reactivity series.

The electrolytic refining of copper is done using the apparatus shown in the figure below.

This is a standard electrolysis setup, where the impure copper (the sample to be refined) is placed as anode and a thin strip of pure copper is placed as cathode. The electrolyte used is copper sulphate solution. When current is passed through the electrolyte, pure copper content from anode dissolves into the electrolyte, and the same amount of copper is deposited on the cathode. One can see that the thickness of the cathode increases.

The soluble impurities present in the anode goes into the solution when the current flows through the setup. The insoluble impurities present in the anode settle down at the bottom of the anode and is called anode mud. Thus, one can refine copper electrolytically.

(a) An alloy of mercury with another metal is called amalgam.

(b) Mineral which contains a very high percentage of a metal and from which the metal can be economically extracted is called an ore.

(c) An element or compound which occurs naturally in the Earth’s crust is called a mineral.

Corrosion refers to the destruction or deterioration of a substance due to its interactions with the surrounding environment. Corrosion is a natural process and occurs when the substance is in contact with air, water, chemicals like acid etc. Corrosion can damage metals causing it to lose properties such as strength and conductivity of heat/electricity.

Corrosion can be prevented by various techniques like painting the surface of the material, galvanizing, oiling, greasing etc.

(a) Copper when in contact with moist carbon dioxide in air gains a green coloured coat over copper. This coat is nothing but copper carbonate formed by the reaction of copper and moist carbon dioxide.

(b) Silver reacts with sulphur present in the air to form a black coating of silver sulphide over the surface of silver.

(a)

Flowchart: Extraction of metals from ores

(b) The characteristics of ionic compounds are,

i. Ionic compounds are hard solids. They are brittle in nature.

ii. They have high melting and boiling point.

iii. They are generally soluble in water, but they do not dissolve in solvents like kerosene, petrol etc.

iv. Ionic compounds conduct electricity in their molten/dissolved form. They do not conduct electricity in their solid form.

OR

(a) Na, K and Li react vigorously with air and water. Hence they cannot be kept in open or in water. They do not react with oil or kerosene. They are stored under oil to avoid contact with air and water.

(b) Pt, Au and Ag are lustrous. They shine brightly when light falls on them. Besides, these metals are easily malleable and ductile to make chains, rings, and so on. Thus they are used in jewellery.

(c) Nitric acid is a strong oxidizing agent. The hydrogen gas obtained from the reaction is quickly oxidized to water (H₂O).

(d) Aluminium is a light metal. It is a good conductor of heat. It has a relatively high melting point. Due to the reactivity of aluminium, it combines with oxygen to form a layer of aluminium oxide over the surface of aluminium. This oxide layer prevents it from further reactivity of the metal. All these reasons make aluminium useful in making cooking utensils.

(e) Iron is more reactive than copper. So iron would displace copper from its salt solutions. In this case, the following reaction will occur:

Fe + CuSO₄→ FeSO₄ + Cu

Hence, there will no longer be copper sulphate solution in the container. It is advised to store chemicals with containers made of less reactive metals.

A metal which has high reactivity can displace a metal with low reactivity from its salt solution. By looking at the reactivity series one can write the order of reactivity:

Na>Mg>Ca>Al>Fe>Cu>Ag

Strictly speaking, all the above-mentioned methods would prevent iron from rusting. Since it is a frying pan, the most suitable method would be to apply a coating of zinc.

Metal oxides have relatively high melting points. Here both iron and calcium are metals, but iron oxide is insoluble in water.

Zinc is a highly reactive metal, and it might react with the contents of the can. Metals of low reactivity are used as food cans.

An alloy is composed of different metals mixed in a certain proportion. So the properties exhibited by one “full” metal cannot be seen in alloys.

Brass is an alloy of copper and zinc and is used in making locks, gears, etc.

Solder has a low melting point, and upon giving a small amount of heat, it turns into liquid and solidifies on cooling.

Galvanisation is the process of applying a protective coating of zinc over the surfaces of steel and iron.

Nickel and chromium are mixed with iron to make stainless steel which does not rust.

Bronze is an alloy of copper and tin and is commonly used in industries.

Metals at the top of the reactivity series are obtained by the electrolysis of their chlorides and oxides.

Magnesium does not react with cold water.

(iii) and (iv)

Impure metal is kept as anode, and a thin strip of pure metal is kept as cathode. The pure metal content present in anode is dissolved into the electrolyte and the same amount of copper gets deposited in cathode.

Na is one of the metals that can be cut with a knife. It is highly reactive to air and water.

Ionic compounds do not conduct electricity because, in solid form, the ions are not freely moving.

Gold (Au) and Silver (Ag) are also known as Noble metals as they are less reactive and exist in their native state in nature.

(i) and (ii)

Silver when exposed to sulphur in air forms a black coat of silver sulphide.

Zinc is more reactive than iron. Hence zinc acts a protective metal to prevent direct contact of iron with moisture, air etc.

False

Metals generally react with acids to give a salt and hydrogen gas.

True

True

True

False

Silver and gold do not react with oxygen at high temperatures.

False

The hydrogen gas obtained from the reaction of metal and nitric acid is oxidized to water by nitric acid.

False

Copper is below hydrogen in the reactivity series. Therefore copper cannot displace H from HCl.

True

True

True