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 ICSE Class 9 Selina Solutions Atomic Structure and Chemical Bonding Ex 4E Q1. (a)           Define covalent (molecular) bond. View Solution (b)           Give an example of covalent bond formed by: (i) Similar atoms (ii) Dissimilar atoms View Solution Q 2.  Covalent bonds can be single, double or triple covalent bond. How many electrons are shared in each? Give an example of each type. View Solution Q3. Show number of bonds in: (i) Ethene molecule (ii) Ethyne molecule View Solution Q4.  An element A has 1 electron in its first shell. It combines with element B having 7 electrons in its third shell. What type of bond is formed? View Solution Q5.  Match the atomic numbers 4, 8, 10, 15 and 19 with each of the following: (a) Element which can form trivalent ion (b) An element with 4 shells. (c) Element with 6 valence electrons. (d) Element which does not form ion. View So...

  Question: In the formation of  (i) oxygen molecule  (ii) carbon tetrachloride molecule,  state the following:  (a) Electronic configuration of nearest inert gas attained.  (b) How many electrons are shared/transferred in bond formation?  (c) Which type of bonds these compounds form?  (d) Draw their orbital diagrams. Solution: (i)                      Oxygen molecule (a)          2, 8 (b)          2 pairs of electrons are shared (c)           Covalent bond (d)          Orbital diagram of oxygen molecule (ii)                    Carbon tet...

  Question: An element X has 2 electrons in its M shell, it forms bond with an element Y which has 7 electrons in its third orbit.  (a) Write the formula of the compound formed.  (b) Which nearest inert gas electronic configuration will element X and Y acquire.  (c) Show by orbital diagram the formation of compound between X and Y. Solution: (a)          XY 2 (b)          Element X will acquire the electronic configuration of Neon (2, 8), and element Y will acquire the electronic configuration of Argon (2, 8, 8). (c)           Orbital diagram for the formation of compound between X, which is magnesium and Y, which is chlorine. Explanation:   M shell means third orbit as the shells are named as K, L , M, ...     X has 2 electrons in its third shell, so its configuration will be 2, 8, 2. Y has 7 electrons in its third sh...

Question: Ion formed by gain of electron(s). Solution: Anion

Question: Bond formed by transfer of electron(s).   Solution: Electrovalent bond

Question: Elements having same mass number but different atomic number.   Solution: Isobars

  Question:   Atoms of the same element differing in mass numbers. Solution: Isotopes

  Question: Metal having valency one. Solution: Sodium Explanation: The configuration of sodium (atomic number 11) is 2, 8, 1. So, it will lose 1 electron to have 8 electrons in its last shell. Thus, its valency is one.

  Question: An element having valency zero. Solution. Neon Explanation: All noble gases have a stable electronic configuration and thus they do not react with any other element, and thus have valency zero.

  Question: A bond formed by transfer of electron(s). Solution: Electrovalent / Ionic bond

 Question: A bond formed by a shared pair of electrons, each bonding atom contributing one electron to the pair. Solution: Single Covalent bond .

  Question: In the formation of magnesium chloride (by direct combination between magnesium and chlorine), name the substance that is oxidized and the substance that is reduced. Solution: Magnesium is oxidised and chlorine is reduced. Explanation: Loss of electrons is oxidation and gain of electrons is reduction. Since Magnesium loses electrons, it is oxidised and chlorine gains electrons, so it is reduced.

Question: The electronic configuration of nitrogen is (2, 5). How many electrons in the outer shell of nitrogen atom are not involved in the formation of a nitrogen molecule? Solution: 2 Explanation: Nitrogen needs 3 electrons to complete its octet because it has 5 electrons its valence shell. So, it shares 3 electrons with the other nitrogen atom in the molecule.  Thus, out of 5, 3 electrons are being shared so 2 electrons will not be involved.

  Question: In the formation of electrovalent compounds, electrons are transferred from one element to another. How are electrons involved in the formation of a covalent compound? Solution: Electrons are mutually shared by the combining atoms in the formation of a covalent compound.

Question:   Name the charged particles which attract one another to form electrovalent compounds. Solution: Cation and anion

 Question: Identify the following reactions as either oxidation or reduction. (i)                      O + 2e - --- → O 2- (ii)                    K – e -   ---- → K + (iii)                 Fe 3+ + e - --- → Fe 2+ (iv)                  Zn -- → Zn 2+ +2e - Solution: (i)                      Reduction (ii)                    Oxidation (iii)             ...

  Question: When a metal atom becomes an ion:  A. It loses electrons and is oxidized  B. It gains electrons and is reduced.  C. It gains electrons and is oxidized.  D. It loses electrons and is reduced. Solution: A. It loses electrons and is oxidized. Explanation: Metals lose electrons and loss of electrons is oxidation.

  Question: The characteristic of an electrovalent compound is that:  A. They are formed by sharing of electrons.  B. They are formed between metals and non-metals.  C. They are formed between two non-metals.  D. They often exist as a liquid. Solution: B Explanation: A. is wrong because electrovalent compound is formed by transfer of electrons and not sharing. Sharing occurs in covalent bond. B. Metals can lose electrons and non-metals can gain electrons. So, there is transfer of electrons from metals to non-metals and thus electrovalent bond is formed between them. C. Two non-metals will be in need of electrons so they will share electrons D. Electrovalent compounds occur as solids.

  Question: Carbon-12 and carbon-14 both show similar chemical properties. Explain. Solution: Chemical properties are determined by the electronic configuration of an atom. Since carbon-12 and carbon-14 have same atomic number, 6, they have same electronic configuration, (2,4) and thus they show similar chemical properties.

  Question: An element has atoms with different mass number. Explain Solution: An element has atoms with different mass number because of the presence of different number of neutrons in their nucleus.

 Question: Atoms combine by transfer and sharing of electron(s). Explain. Solution: Atoms combine to attain the stable electronic configuration of the nearest noble gas which is attained by the transfer or sharing of electrons.

  Question: Mass of an atom is concentrated inside the nucleus of the atom. Solution: Since electrons have negligible mass, the mass of an atom is due to the protons and neutrons. Since protons and neutrons are present in the nucleus of an atom, mass of the atom is concentrated inside the nucleus of the atom.

  Question: Metal M forms a chloride with the formula MCl 2 . What type of bond is in MCl 2 . Write the formula of the compound when M combines with sulphur, oxygen and nitrogen. Solution: Electrovalent bond. Formula of compound when M combines with: 1. Sulphur- MS 2. oxygen- MO 3. Nitrogen-  M 3 N 2 Explanation: Since M is a metal, it will lose electrons and we know that the electronic configuration of chlorine (atomic number 17) is 2, 8, 7, which will accept 1 electron to complete its octet. Since, there is complete transfer of electrons from M to chlorine, it will be an electrovalent bond. In  MCl 2 , valency of chlorine is 1 (from its electronic configuration 2, 8, 7) as it accepts 1 electron. So, valency of M must be 2 ( think of criss-cross method). Now, valency of M is 2 . 1. Valency of sulphur is 2. So apply criss cross method M   S 2      2 Both 2 will get cancelled and so the formula will be MS. 2. Valency of oxygen is 2. Apply criss cro...

Question:  State the type of bonding in the following molecules.  (a) Water  (b) Calcium oxide  (c) Hydrogen chloride Solution: (a) Covalent bond (b) Electrovalent bond (c) Covalent bond Explanation: (a) In water, Hydrogen (electronic configuration, 1) needs 1 electron to attain the configuration of the nearest noble gas, Helium  and Oxygen (electronic configuration, 2, 6) needs 2 electrons to attain the configuration of the nearest noble gas, Neon. Since both of them are in need of electrons, they will share electrons and will form a covalent bond. (b) calcium with electronic configuration 2, 8, 8, 2 will donate 2 electrons and oxygen with electronic configuration 2, 6 will accept two electrons. Thus, there will be complete transfer of electrons and thus electrovalent bond is formed. (c) Hydrogen with electronic configuration 1 needs 1 electron to attain the configuration of the nearest noble gas, Helium. Chlorine with electronic configuration 2, 8, 7 will acce...

  Question: Give the orbital diagram of hydrogen chloride. Solution: Orbital diagram of hydrogen chloride

  Question: Give the orbital diagram of methane. Solution: Orbital diagram of Methane  (CH 4 )

  Question: Give the orbital diagram of nitrogen. Solution: Orbital diagram of Nitrogen

  Question : Give the orbital diagram of magnesium chl oride Solution: Orbital diagram of magnesium chloride

  Question: An element M burns in oxygen to form an ionic compound MO. Write the formula of the compounds formed if this element is made to combine with chlorine and sulphur separately. Solution: MCl 2 and MS Explanation: Valency of Oxygen is 2. Since formula of oxide is MO, valency of M must be 2 so that both the two get cancelled and the formula becomes MO. So, valency of M is 2. Now, valency of chlorine is 1 By criss-cross method, M    Cl 2       1 1 goes to M and 2 goes to Cl So, the formula is  MCl 2 . Similarly, valency of sulphur is 2. By criss-cross method, M   S 2     2 Both the two get cancelled, and so the formula is MS.

 Question: Name two compounds that are covalent when taken pure but produce ions when dissolved in water. Solution: Hydrogen chloride and ammonia Explanation: Polar covalent compounds produce ions when dissolved in water.  Ammonia  and hydrogen chloride are polar in nature.