Study Portal 16 – Chapter 16

Chemical Reactivity



Q1.      Fill in the blanks with appropriate words.

  1. i) Electrons are involved in the chemical reaction.
  2. ii) Metal are solid in nature while non-metal are electro negative in nature.

iii)     The Alkali Metals are most reactive metals.

  1. The noble gases are least Reactivity of all elements.
  2. When difference between electro negativities is more than 2, the nature of bond is
  • The alkali metals found only in oxidation
  1. Iron is a hard metal while sodium is soft
  2. Among halogens Fluorine is most reactive.
  3. The chemical reaction involves a chemical
  • NaOH is also known as Caustic Soda.

Q2.      Choose the correct answer.

  1. i) The metals are characterized by:

(a) conduction of electricity

(b) mealbility and ductile nature

(c) lustrous nature

(d) all of above

  1. ii) In a group the reactivity of metals:

(a) increases              (b) decreases

(c) no effect at all      (d) increases first and then decreases

iii)     The electro negativity is the tendency of an atom:

(a) to attract electron pair of bond

(b) to repel electron pair of bond

(c) to attract another atom (d) to repel another atom

  1. iv) The halogen means:

(a) water producer                         (b) salt producer

(c) taste producer                           (d) stream producer

  1. v) The noble gases do not react due to:

(a) smaller size                                 (b) less charge

(c) stable electronic structure   (d) high electro negativity

Q3.      Answer the following questions.

  1. i) Based on speed how many types of chemical reactions exist.

Ans.  The chemical reactions on the basis of their speed are divided into 3 categories. The slow reaction, moderate reaction and fast reactions. Rusting of iron is the example of slow reaction, the organic reactions mostly are of moderate speed and reactions between the ionic compounds are very fast.

  1. ii) Define term Metals.

Ans.  Metals are the elements (Except Hydrogen) which are electro positive and from cations by losing electron Metal can be categorized.

  1. a) Very reactive:- potassium, sodium, calcium etc
  2. b) Moderately reaction:- zinc, iron, and lead.
  3. c) Least reactive or noble:- copper, mercury and gold.

iii)     How electro positive character of metals show trend in periodic table?

Ans.  The metals are electro positive in nature i.e. they tend to lose electrons and hence gain positive charge.

  1. What is electro negativity? How electro negativity shows variation in periodic table?

Ans.  The tendency of an element to accept an electron to form an-ion is called its electro negative character. The element having high electron affinity or high electro negativity have high tendency to gain electrons and negative ion. The electro negative character decreases as we go down in a group of periodic table.

  1. v) Write down three most abundant elements of human of earth crust.

Ans.  Three most abundant elements of human body are oxygen 65%, carbon 18% and hydrogen 10%.

  1. vi) Write chemical equation of three reactions of water.

2Na + 2H2O      2NaOH +H2

C + H2O   CO + H2 (water gas)

CO2 + H2O                         H2CO3

vii)          What is caustic soda? Write three uses of caustic soda.

Ans.  Caustic soda is a white opaque compound, crystalline sold, highly soluble in water, strong alkali.


  1. Extensively in the preparation of soap
  2. In textile and paper industries
  3. As a laboratory reagent

viii)         Differentiate between noble gases and noble metals?

Ans.  The elements of group eighteen are called noble gases. They not react with other elements. The chemistry of metals is characterized by their ability to lose electrons to form cation. Some metals are relatively difficult to oxidize e.g. Cu, Ag, Au and Pt these metals are often called noble metals.

  1. ix) Writes uses of halogens.

Ans.  The halogens are used in bleaches, water purification, photography, insecticides, plastics, dyes and explosives etc.

  1. x) Differentiate between soft and hard metals.

Ans.  The alkali metals are very soft, malleable and light metals. The can be easily cut with knife. The alkali metals are characterized by the presence of one electron in outer most ‘s’ orbital. The acquire the configuration of noble gases e.g. Li, Na, K, Rb, Cs, and Fr. Alkaline metals show greater specific gravities greater hardness and higher melting points e.g. Be, Mg, Ca, Sr, Ba, and Ra.

S# Soft Metal Hard Metal
1 They have low melting point and boiling point They have high melting point and boiling point
2 They have less binding force between atom They have more binding force between atoms
3 Their compounds are white Their compounds are mostly colored
4 Examples s-block elements Examples d-block and f-block elements

Q4.      Answer the following questions with reasoning.

  1. i) What is the relation between chemical reactivity and the energy of a system?

Ans.  Chemical reactivity is measured by the relative tendency of an element to lose or gain electrons in chemical reactions. A physical or a chemical change is almost always accompanied with either absorption or evolution of heat (Energy). Ionization energy is the measure of tendency of an atom to lose its valence electrons. Ionization energy of an atom depends upon the size of atom and nuclear charge on valence electrons.

  1. ii) Explain what electronic configuration Mg and Br2 achieve after they react.

Ans.        Electronic configuration of:

Mg = 1S2, 2S2, 2P6, 3S2

Br        = 1S2, 2S2, 2P6, 3S2, 3P6, 4S2, 3d10, 4p5

Mg + Br2      MgBr2

When Mg and Br react they form MgBr2 and the total no. of electrons become 47. So they achieve the electronic configuration near to Noble gas Xe.

iii)           Why k is more reactive than Mg?

Ans.  ‘K’ is a alkali metal and Mg is alkaline metal. Alkali metals are very reactive but alkaline metal are fairly reactive. Alkali metals are highly electro positively while alkaline metals are less electro positively. So k is more reactive than Mg.

  1. iv) Explain why group 18 elements do not react?

Ans.  The group 18 elements are generally called inert gases because they are chemically inert substances and exist only in Free State. These gases are also called noble gases. The chemical inertness of these gases is due to their stable electronic configuration. Except helium (atomic number 2) atoms of all other gases have fully occupied valence shells. nS2, nP6. Thus the outer most S and P orbital are completely filled and therefore atoms of these elements do not react.

  1. v) Among halogen which member is most reactive and why?

Ans.  The electro negativity of F(4.0) is the highest and is even greater than O (3.5) other halogens are less electronegative than oxygen. So fluorine is most reactive than other halogens.


Q5.      What is the metal? How they differ from non-metals?

Ans.  Metals:- metals are the elements which are electro positive and form caption by losing their valence shell electron easily. As concerned to reactivity, metals show mix behavior, some of metals are very reactive e.g. the alkali metals and some are quite inert. Metals are good conducting electricity and heat; they can be transformed in any desired shape. Metals can be drawn into wires of small diameters. The metals are shiny, metals generally form basic oxides.

Non-Metals:- non-metals covers a general spectrum behavior, poor conductors of heat and electricity when compared to metals, they form acidic oxides in solid form they are dull and brittle, rather than metals which are lustrous ducite or malleable usually have lower densities than metals. They have significantly lower melting and boiling points than metals.


Q6.   What is the difference between reactivity of metals and non-metals?

Ans.  Chemical reactivity is measured by the relative tendency of elements to lose or gain electrons in chemical reactions.

  1. The reactivity of metals is measured in term of their tendency to lose electrons from their outermost shell. Whereas that of a non-metal is measured in terms of its tendency to gain electrons to form an anion.
  2. The reactivity of metals is also increases down the group and reactivity decrease along the periods. But this is not in the case of non-metals where the electro negative character counts, rather then the electropositive character, which is just opposite to the electropositive character.


Q7.   What is electro negativity? How it affects the nature of the chemical bonding and bond polarity.

Ans.  The term electro negativity is defined as the ability of an atom to attract shared electron pair of bond in a compound. The electro negativity of an element is the net effect of electron affinity and first ionization potential. Electro negativity is the property of non-metals because non-metals have lower size and more nuclear charge, so they attract the shared electron pair, this ability of attraction electron pair decreases as the size increases down the group. In the periodic table, electro negative values decreases down the group and increases along the period. Thus ‘F’ has the greatest electro negativity value of 4.0 and ‘Cs’ has lower value of 0.7. The electro negative values are very often used in prediction of reactivity and the bond type. The elements with high electro negativity value are more reactive e.g. the ‘F’ with the highest electro negativity value of 4.0 is the most reactive element of the periodic table. Moreover the electro negativity is also utilized to calculate the bond type. If electro negativity difference is 1.7 the bond is 50% covalent and 50% ionic. When the difference of electro negativity is greater than 1.7 bonds is ionic and with the increase in this difference ionic character also increases. When difference is less than 1.7 bonds is covalent. If difference is less than 0.5 bonds is non-polar and if difference is greater than 0.5 but less than 1.7 bonds is polar covalent type.

Q.8.     Compare the reactivity of alkali and alkaline earth metals?

Ans.  The alkali metals contains one valence electron, easily lost by applying small ionization energy so called reactive in nature as compare to alkaline earth metals which contains two valence electrons which required high energy than alkali metals. Hence alkali metals are more reactive than alkaline earth metals. Their reactivity down the group increases because of the increase of atomic size.

Q9.      What are halogens? Discuss their chemical reactivity.

Ans.  The elements in group VII-A are called halogens. The name halogens is derived from the Greek words ‘Halous’ meaning ‘Salt’ and ‘Gen’ meaning former. Halogens include fluorine, chlorine, bromine iodine and astatine.

All halogens are reactive non-metals. They all exist as diatomic molecular substances.

Fluorine      pale yellow gas.

Chlorine     Greenish yellow gas

Bromine     Reddish- Brown liquids

Iodine         Bluish- black solid.

Reactivity of the Halogens:- All the halogens react with metals to form salts called halide. In these reactions metal are oxidized, so halogens act as oxidizing agents. Fluorine is the most reactive elements known. Chlorine is less reactive, but combines vigorously with many metals. For instance sodium metals burns in chlorine gas to form sodium chlorine.

2Na + Cl2            2NaCl

The reactivity of halogens decrease down the group. Thus the order of decreasing oxidizing power is F2 > Cl2 > Br2 > I2

The halogens react with hydrogen to form hydrogen halides.

H2 + X2      2HX

When X = F , Cl, Br, I.

Q.10.   Give an account on the properties of non-metals also describes their importance.

Properties of non-metals

  1. Non-metals are most liquids or gases but some non-metals are solids.
  2. Non-metals are usually non-flexible.
  3. They are difficult to mould and convert them into wires and sheets.
  4. Atoms are bonded by covalent bonding.
  5. Non0-metals are usually non-conductors but few of them conduct electricity.
  6. Non-metals do not have transfer heat.
  7. Non-metals do not have much brightness even on polishing.
  8. Non-metals absorb light.
  9. Non-metals are usually light and have low density.
  10. Non-metals having usually low melting and boiling points.
  11. Non-metals ions bear negative charge e.g. Cl-1, O-2, N-3, but some bear positive charge as well e.g. H+1.
  12. Oxides of non-metals are acidic e.g. SO2, CO2
  13. Non-metals have tendency to gain electrons.

Importance of non-metals:- Although non-metals are fewer than metals, yet they are highly significant, they are equally important for human beings, Animals and plant. In fact life would not have been possible without the presence of non-metal on earth.

  1. Major components of earth’s crust, oceans, and atmosphere are non-metals. Oxygen has the highest percentage in earth’s crust (47%) and oceans (86%) and it is second (21%) to nitrogen in atmosphere. It indicates the importance of oxygen in nature different cycles have been established naturally.
  2. Non-metals are essential part of the body structure of all living things. Human body is made up of about 28 elements. But about 96% of the mass of the human body is made up of just 4 elements i.e. O2 (65%), C (18%), H (10%) and N (3%) similarly plant bodies are made up of cellulose, which is composed of C, H and O2.
  3. Life owes to non-metals as without O2 and CO2 life would not have been possible. These gases are essential for the existence of life.
  4. All eatable which are necessary for the growth and development of body that are made up of non-metals
  5. The essential compound for the survival of life of both animals and plants is water, which is made up of non-metal. We can survive without water for days but not for a long period.
  6. Important non-metal nitrogen which is 78% of atmosphere is necessary for the safety of life on earth.
  7. Non-metals are playing essential role for the communication in life. All fossil fuels which are major source of energy are made up of C + O2.
  8. Non-metals protect us in a way; the clothes we wear are made of cellulose or polymer. Even all the particles, insecticides, fungicides and germicides consist of non-metals are major constituents.


Q.11.   Complete and balance the following chemical reactions

  1. H2O + Br2     
  2. NaOH + Br2
  3. K + O2      
  4. Mg + H2O
  5. CH4 + O2      


  1. 2H2O + 2Br2            4HBr + O2
  2. 6NaOH + 3Br2            NaBrO3 + 5NaBr + 3H2O
  3. K + O2            KO2
  4. Mg + 2H2O            Mg (OH)2 + H2 + heat

CH4 + 2O2                               CO2 + 2H2O + heat

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