Atomic Structure Dalal Simplified Class-9 ICSE Chemistry Solutions
by Dr Viraf J Dalal Middle School Chemistry Allied Publishers
Atomic Structure Dalal Simplified Class-9 ICSE Chemistry Solutions Chapter-4. We Provide Step by Step Solutions of Exercise/Lesson -4 Atomic Structure with Additional Questions , Previous Year Questions and Unit Test-4 of Dr Viraf J Dalal Middle School Chemistry Allied Publishers. Visit official Website CISCE for detail information about ICSE Board Class-9.
Atomic Structure Dalal Simplified Class-9 ICSE Chemistry Solutions Chapter-4.
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Previous Year Questions of Atomic Structure and Chemical Bonding for ICSE Class-9 Chemistry
Define the terms : atomic number, mass number and electron.
Atomic number [Z] : “Is the number of protons in the nucleus of an atom.”
OR “Is the number of positive charges in the nucleus of its atom.”
OR “Is the number of electrons in the complete atom.”
Z = P = e
Mass number [A] : “Is the total number of protons and neutrons in the atom of an element.”
A = P + n
Electron [e] : “A sub-atomic particle having a unit negative charge and mass equal to 1/1837 of that of hydrogen atom, revolve round the nucleus.” [-1e0]
From the symbol 4/2 He for the element helium, write down the mass number and the atomic number of the element.
Sulphur has an atomic number of 16 and a mass number of 32. State the number of protons and neutrons present in the nucleus of sulphur.
Protons → Atomic number = 16 = P
Number of Neutrons = A – P = 32 – 16 = 16
Give a simple diagram to show the arrangement of the electrons in an atom of sulphur.
In sulphur atom.
Number of electrons = P = e = 16
2412Mg and 2612Mg are symbols of two isotopes of magnesium. Compare the ‘ atoms of these isotopes with respect to :
- the composition of their nuclei.
- their electronic configurations.
- give the reason why the two isotopes of magnesium have different mass numbers.
Chlorine is an element of atomic number 17. It is a mixture of two isotopes having mass number of 35 and 37.
- What is meant by “atomic number of an element” ? What do you understand by an ‘atom’
- Write down the electronic configuration of the chlorine atom.
- State the number of protons, electrons and neutrons in the following isotopes: 35Cl17, 37Cl17
- Explain why the two atoms in (iii) above have the same chemical reactions.
- If molten magnesium chloride is electrolysed suggest a suitable electrode [anode].
- Atomic number is the number of protons in an atom.
Atom : The basic unit of matter is the smallest particle of an element which can take part in a chemical reaction.
- Number electrons in chlorine atom is 17 [2, 8, 7] and their distribution in various shells in K = 2, L = 8, M = 7.
- Two isotopes of chlorine are
3517Cl number of protons = 17 and number neutrons = 35 – 17 = 18
Number of electrons = 17
3717 Cl number of protons = 17
electrons = 17
neutrons = 20 (37 – 17)
- Two isotopes of chlorine have same chemical reactions as their atomic number i. e. number of electrons i.e. electronic configuration is same (17).
- When molten magnesium chloride is electrolysed suitable anode used is carbon.
Five atoms are labelled V to Z
- Which one of these atoms (1) contains 7 protons ; (2) has an electronic configuration 2, 7 ?
- Write down the formula of the compound formed by atoms X and Y.
1. Contains 7 protons
Z – has atomic number of Z = 7
2. Has atomic configuration (2, 7)
W – atomic number = of electrons = 9 (2, 7)
(ii) X-atomic number 3
= number of electron = (2, 1)
∴ X has valency [1+] Y-atomic number = 8
= number of electrons = (2, 6)
Elements X, Y, Z have atomic numbers 6, 9 and 12 respectively. Which one :
- forms anion – negative ion ;
- forms cation – positive ion ;
- has 4 electrons in the outermost orbit. [Y, Z, X]
Atomic number of
X = 6 = number of electrons (2, 4)
∴ X has 4 electrons in outermost orbit.
Y = 9 = number of electrons (2, 7)
∴ Y form anion = negative ion
Z = 12 = [2, 8, 2] ∴ Z forms cation – positive ion.
Ordinary chlorine gas has two isotopes : 3517Cl and 3717Cl in the ratio of 3 : 1. Calculate the relative atomic mass [atomic weight] of chlorine.
The atom of aluminium is represented by 27Al13. Write down the number of
(d) the arrangement of electrons
in the different orbits or shells in one atom of aluminium.
Name the clement which does not contain any neutrons in its nucleus.
Element is [H] Hydrogen.
Elements A, B and C have atomic numbers 9, 20 and 10 respectively.
- State which one is (1) a non-metal, (2) a metal, (3) chemically inert.[A,B,C]
- Write down the formula of the compound formed by two of the above elements.[BA2]
Define : Proton, Electron, Neutron.
Proton is subatomic particle found in nucleus of atom having unit positive charge, mass = 1 hydrogen atom.
Found in nucleus of atom and number of protons in an atom = number of electrons.
Electron = e = is sub atomic particle revolving around the nucleus of atom having
unit – ve charge, mass = 1/1840 of 1 hydrogen atom and number of electrons = number of protons.
Neutrons = n = is sub-atomic particle found in nucleus of atom, having no charge, mass = mass of 1 proton.
Write down the electronic configuration of the following (i) 2713X, (ii) 3517Y.
Write down the number of electrons in X and neutrons in Y and the formula of the compound formed by X and Y.[XY3]
According to the Dalton’s Atomic Theory, atoms of the same element are identical in all respects. But according to the Modern Atomic Theory, this postulate is proved wrong. Explain.
According to modern atomic theory atoms of the same element may not be alike in all respect.
e.g. isotopes of chlorine 3517Cl and 3717 Cl have different atomic masses 35 and 37. This proves Dalton’s Atomic Theory wrong.
What are isotopes.
Isotopes : “Atoms of the same element having same atomic number, different mass number and similar chemical properties.”
Write down :
- the mass number of the atom having 20 neutrons and 15 protons.
- the number of neutrons in the nucleus of an atom having atomic number 17 and mass number 37.
- Mass number (A) = Neutrons (n) + Protons (p)
Mass number = 20 + 15 = 35
- A = n + p (At. No.) A is mass number
37 = n + 17
Number of neutrons = n = 37 – 17 = 20
What is a proton ? What is the significance of the number of protons found in the atoms of each of the different elements.
Proton : “Is positively charged sub-particle of atom present in nucleus.”
Proton helps in determining and understanding the structure and behaviour of an atom. Elements are arranged on the bases of number of protons in their respective atoms.
What is the relation between the number of protons and the number of electrons in an atom.
The number of protons in an atom is equal to the number of electrons.
What would be the reason for an element to have atoms with differing mass numbers.
Atoms of same element have different mass number as these isotopes have different physical constants i.e. different physical properties. OR “Atoms have different number of neutrons.”
Copy and complete the following table relating to the atomic structure of some elements :