Viraf J Dalal Chemistry Class 9 Solutions and Answers
Compound X consists of molecules Bonding in X will be :
A : ionic
B : electrovalent
C : covalent
D : molecular.
C : covalent
What is a lone pair of electrons. Draw an electron dot diagram of a hydronium ion (with lone pair).
The electronic configuration of nitrogen is 2, 5. How many electrons in the outer shell of a nitrogen atom are not involved in the formation of a nitrogen molecule.
2 electrons in the outer shell of each nitrogen atom are not involved in sharing during formation of nitrogen molecule.
What is the term defined in a bond formed by a shared pair of electrons each bonding atom contributing one electron to the pair.
Single covalent bond.
Draw the atomic orbit structure of carbon tetrachloride and state the type of bond present in it
Sodium chloride – covalent bond /ionic bond/covalent and coordinate bond.
Carbon tetrachloride – covalent bond/ionic bond/covalent and coordinate bond.
(i) In covalent compounds, the bond is formed due to the ____ (sharing/ transfer) of electrons.
(ii) A molecule of ____ contains a triple bond, (hydrogen, ammonia,nitrogen)
(i) In covalent compounds, the bond is formed due to the sharing of electrons.
(ii) A molecule of nitrogen contains a triple bond.
The molecule containing a triple covalent bond is :
Explain the bonding in methane molecule using electron dot structure.
Formation of methane molecule – Non-polar covalent compound :
Explain the term ‘chemical bond’ & ‘chemical bonding’?
- Chemical bond : The linkage force which acts between two or more atoms to hold them together as a stable molecule is called a chemical bond.
- Chemical bonding : The concept of chemical bond is called chemical bonding.
State why noble gases have stable electronic configuration while atoms of other elements have unstable electronic configuration.
Noble gases have stable electronic configuration because they have their outermost orbit completely filled with electrons, 2 incase of the helium and 8 electron in rest of the noble gases.
Atoms of other elements are unstable as they do not have electronic configuration of their nearest noble gas i.e. They have uncomplete valence shell and do not have their outer shell completely filled.
Explain in brief how atoms of other elements other than noble gases, attain stable electronic configuration of the nearest noble gas.
Elements of atoms of other than noble gas attain stable electronic configuration by lose of electron/s incase they have 2, 3 valence electron or by gain of electron/ s incase they have 5, 6 or 7 valence electrons or by sharing of electrons.
Define the terms
- Electrovalent or ionic bond
- Electrovalent or ionic compound
- covalent bond
- covalent compound
with suitable examples wherever required.
- Electrovalent or ionic bond : The chemical bond formed between two atoms by transfer of one or more electrons from the atom.
- Electrovalent or ionic compound : The chemical compound formed as a result of transfer of one or more electrons from atom.
- Covalent bond : Sharing of electrons between two atoms form Covalent bond.
- Covalent compound : The chemical compound formed due to mutual sharing of electrons between the given pairs of atoms forming a covalent bond is called covalent compound.
State what is meant by :
(a) duplet rule
(b) octet rule.
(a) Duplet rule : For an atom to achieve stable electronic configuration it must have 2 electrons in its first shell if first shell is valence shell like noble gas Helium it is called duplet rule.
(b) Octet rule : For achieving stable electronic configuration an atom must have 8 electrons in it’s valence shell like noble gas other than helium.
Sodium chloride is formed os a result of — transfer of electrons from metallic sodium atom to non-metallic chlorine atom. With the help of atomic orbit structure diagram show the formation of sodium chloride. [Atomic numbers: Na = 11, Cl = 17]
Sodium chlorine (NaCl)
Atomic orbit structure :
Atomic number of calcium is 20 and of oxygen is 8. State the number of electrons – calcium loses & oxygen gains to attain stable electronic configuration of the nearest noble gas – during formation of electrovalent molecule, calcium oxide.
Atomic number of calcium is 20, electronic configuration 2, 8, 8, 2 has 2 valence electrons which Ca loses as it is not possible to gain 6 electron (to have octet arrangement) to have stable nearest noble gas K configuration.
Oxygen O 8=2,6 has 6 valence electrons and gains 2 electrons to attain stable nearest noble gas Ne configuration (octet)
∴ Calcium oxide CaO electrovalent molecule is formed.
Explain with the help of atomic orbit structure diagram the formation of calcium oxide.
Calcium oxide (CaO)
Give a reason why – in the formation of electrovalent compound – magnesium chloride, one magnesium atom combines with two chlorine atoms to give magnesium chloride, (at. no.: Mg = 12, Cl = 17]
At. no. of Mg = 12
electronic configuration 12 = 2, 8, 2
Nearest noble gas Ar = (2, 8)
Mg-atom loses 2 electrons from its valence shell and becomes stable configuration and cation Mg2+
But Cl at. no. 17 electron configuration 8, 7 has 7 valence electrons.
It accepts 1 electron to have stable nearest noble gas configuration of argon (2, 8, 8)
So to accept 2 electrons lost by Mg atom there must be 2 Cl-atom. Hence to form MgCl2
One magnesium atom and two chlorine atoms are required.
‘Formation of hydrogen molecule takes place by sharing of electrons’. Give a reason why the molecule of hydrogen is not formed by — transfer of electrons.
Atom of hydrogen has unstable electronic configuration and has 1 valence electron. To attain stable electronic configuration. To attain stable electronic configuration of nearest noble gas configuration i.e. 2 electrons in valence shell (Duplet rule) share one electron.
Both atoms of hydrogen in hydrogen molecule are short of 1 electron in valence shell and to have stable electronic configuration of nearest noble gas they share 1 electron each in valence shell and no transfer of electron takes place in that case H-atom will cease to exist.
Draw the atomic orbit structure diagram for formation of —
(a) hydrogen molecule
(b) chlorine molecule
(c) oxygen molecule
(d) nitrogen molecule [at.no.: H = 1, Cl = 17, O = 8, N = 7]
Give reasons for formation of a single covalent bond between two chlorine atoms and a double covalent bond between two oxygen atoms – during formation of a covalent chlorine molecule and formation of-a covalent oxygen molecule, respectively.
At. no. of Cl-atom is 17
17 = 2, 8, 7
each atom has 7 valence electrons which one atom cannot lose 7 electron to other nor it can accept one electron from other Cl atom as it will be left will 6 electrons. Hence both atoms of chlorine share 1 electron and both have 8 electrons in valence shell i.e. both have stable configuration and since both share 1 electron Cl – Cl forms single covalent bond.
O 8 = 2,6 each atom of oxygen atom has 6 valence electrons and short of 2 electron
to have stable octet. Both of the atoms cannot lose 6 electrons nor gain 2 electrons as explained above. Hence both atoms share 2 electrons each and each has 8 electrons revolving in valence shell and forms oxygen molecule with double covalent bond.
Draw the atomic orbit structure diagram for formation of a —
(a) water molecule
(b) ammonia molecule [at.no.:H = 1, O = 8, N = 7]
Hydrogen atom has 1 electron in first valence shell and O – atom has 6 electrons in valence shell
State why water has two lone pairs of electrons in its covalent molecule while ammonia has one lone pair.
In water there are two shared as there are 2H-atoms pair and two lone pairs.
In ammonia there are three shared pairs as there are 3H-atoms and one lone pair.
With the help of ail atomic orbit structure diagram – explain the formation of —
(a) carbon tetrachloride
(b) methane, [at. no.: C = 6, Cl = 17, II = 1]
Atomic orbit structure diagram of
(a) CCl4 (carbon tetrachloride)
C atomic number 6 = 2, 4
Give a reason why one atom of carbon — shares four electron pairs, one with each of the four atoms of chlorine during the formation of covalent molecule — carbon tetrachloride.
C-atomic no. = 6 = 2, 4, has 4 valence electrons, it cannot lose 4 electrons also it cannot gain 4 electrons for energy considerations. Hence C atom shares valence electrons. Each atom of Cl has 7 electrons in outer most orbit and can gain 1 electron. Hence to attain octet i.e. 8 electrons in valence shell it needs 4 Cl-atoms to form covalent molecule of CCl4.
Chemical Bonding – Unit Test Paper 4
Q.1. Name the following :
An electrovalent compound formed by transfer of one electron from a metallic atom to a non-metallic atom.
The electrovalent compound is sodium chloride (NaCl)
A covalent hydrocarbon molecule, having four single covalent bonds.
A covalent hydrocarbon molecule having four single covalent bonds is methane
A covalent molecule, having two lone pair of electrons.
A covalent molecule having two lone pair of electrons is water
A covalent molecule having a triple covalent bond.
A covalent molecule having triple covalent bond is nitrogen (N = N)
A covalent molecule having two shared pairs of electrons in its molecule.
A covalent molecule having two shared pairs of electrons in its molecule is oxygen (O = O).
Q.2. Give reasons for the following :
To attain stable electronic configuration of the nearest noble gas —
Hydrogen atom – needs one electron.
11H needs 1 electron to attain nearest noble gas He configuration i.e. 2 electrons in first valence shell (Duplet-rule)
Oxygen atom 168O – needs two electrons.
168O=2,6 to achieve nearest noble gas Ne, electronic configuration (octet-rule) Oxygen atom has 2 electrons short of 8.
Nitrogen atom 147N – needs three electrons.
147N=2,5 Nitrogen atom has 3 electrons short of 8 electrons in valence shell to attain nearest noble gas Ne configuration, (octet rule).
Carbon atom 126C – needs four electrons.
126C=2,4 C – atom has 4 electrons short of 8 electrons in valence shell. It needs 4 electrons to attain nearest noble gas Ne electronic configuration.
Chlorine atom 3517Cl – needs one electron.
3517Cl=2.8,7 atom Has 1 electron short of nearest noble gas Ar configuration (octet rule).
Q.3. Complete the table given below, pertaining to formation of covalent compounds :
(a) Single i.e. 1 covalent bond
(b) 3 covalent bonds
(c) 2 covalent bonds
(d) 1 covalent bond
(e) 1 covalent bond
Q.4. Differentiate between the following with a suitable example :
Lone pair & shared pair of electrons.
Difference between lone pair and shared pair :
- Lone pair : A pair of electrons which is alone i.e. does not share with electron of other atom to complete valence shell of both at m.
- Shared pair : A pair of electrons, one froms each atom are share for both atom to complete their respective valence shell.
Example, In case of water
Shared pair makes complete valence shell (Duplet) of hydrogen and octet in oxygen.
Lone pair is used in making octet of oxygen only.
Duplet rule & octet rule.
- Duplet rule : If valence shell is in first orbit (or K orbit), it has maximum of 2 electrons i.e. He.
- Octet rule : An atom can have maximum of 8 electrons in valence shell.
Stable electronic configuration & unstable configuration.
- Stable electronic configuration : When an atom of an element has an valence shell of 2 electrons, only in case of noble gas He i.e. in 1st outer most shell or 8 valence electrons in valence shell like other noble gases, that is called stable electronic configuration.
- Unstable electronic configuration : Atoms of the elements other than noble gases have their valence shell incomplete i.e. have 1, 2 … 7 electrons and are reactive. They have unstable electronic configuration.
Electrovalent bond & covalent bond
- Electrovalent bond : “A bond formed between metal and non-metal by transfer of electron in called electrovalent bond e.g. (NaCl)
- Covalent bond : “Bond formed between non-metal or molecule of gas by sharing equal number of electrons by each atom is covalent bond e.g. Cl – Cl, H – H,
Single covalent bond & triple covalent bond.
- Single covalent bond : “Sharing one pair of electrons betwen two reacting atoms So that each atom attains stable electronic configuration of the nearest noble gas Helium results in the formation of single covalent bond.”
- Triple covalent bond : “A bond formed as a result of sharing three pairs of electrons between two reacting atoms so that each atom attain stable electronic configuration of nearest noble gas is called triple covalent bond.”
Q.5. Atomic numbers of the following elements are given below:
A = 8; B = 7; C = 17; D = 11; E = 20
State which of the above is a divalent metal.
State which of the above is a non-metal.
State the type of bonding between two atoms of ‘A’.
Type of bonding between two atoms of ‘A’ is Double covalent bond
State the type of bonding between ‘D’ & ‘C’
Type of bonding between ‘D’ and ‘C’ is Electrovalent bond
State the number of covalent bonds formed in a molecule of ‘B2’
Covalent bonds formed in molecule of B2 is Triple covalent bond
Q.6. The representation below shows the outline formation of an electrovalent compound.
If the atomic number of element ‘X’ is 11 and of element ‘Y’ is 17 —
State why an electron is transferred from ‘X’ to ‘Y’ during the formation of ‘X Y’
X— has 1 electron in valence shell which it can lose and become stable.
Y — has 7 electrons in valence shell and by gaining 1 electron attains stable octet.
Give a reason why electrons are not shared between ‘X’ & ‘Y’ — during the formation of ‘XY’
Both X and Y can not share equal number of electrons to attain their stable configuration. Moreover X has 1 electron to lose and Y needs 1 electron to attain stable valence shell.
State the difference between ‘X’ and ‘X1+’
X is atom and has no charge X1+ is ion and has unit +ve charge called cation.
Does ‘Y1-’ have a stable or an unstable electronic configuration.
Y1- has stable electronic configuration.
If a compound is formed from atom A [at. no.19] and an atom Y [at. no. 17], would the compound ‘AY’ be an electrovalent or covalent compound. Give reasons.