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CHEMISTRY [5 Mark Question Answer]

The Periodic Table · ICSE STD 9 (ICSE - English Medium). 4 questions.

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[5 Mark Question Answer]

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Question 15 Marks
Match column A with column B.

Column A

Column B

(a) Element short by 1 electron in octet

(i) Transition elements

(b) Highly reactive metals

(ii) Noble gases

(c) Non-reactive elements

(iii) Alkali metals

(d) Elements of groups 3 to 12

(iv) Alkaline earth metals

(e) Radioactive elements

(v) Halogens

(f) Elements with 2 electrons in the outermost orbit

(vi)Actinides
Answer

Column A

Answers

(a) Element short by 1 electron in octet

(v) Halogens

(b) Highly reactive metals

(iii) Alkali metals

(c) Non-reactive elements

(ii) Noble gases

(d) Elements of Groups 3 to 12

(i) Transition elements

(e) Radioactive elements

(vi) Actinides

(f) Elements with 2 electrons in the outermost orbit

(iv) Alkali earth metals
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Question 25 Marks
Two elements $P$ and $Q$ belong to the same period of the modern periodic table and are in group $1$ and group $2$, respectively. Compare the following characteristics in the tabular form.
  1. Number of electrons in their atoms
  2. Their tendency to lose electrons
  3. Their metallic characters
  4. Formation of their oxides
  5. Formulae of their chlorides
Answer
As elements P and Q belong to the same period of the modern periodic table and are in group 1 and group 2, they belong to alkali metals and alkaline earth metals, respectively.
Characteristic P Q
(a)Number of electrons in their atoms Valence electron $= 1$ Valence electrons $= 2$
(b) Their tendency to lose electrons Can easily lose electrons They will lose electrons easily but not as easily as alkali metals can.
(c) Their metallic characters P is more metallic Q is less metallic than P
(d) Formation of their oxides React rapidly with oxygen in the air
$4Na + O_2→ 2Na_2O$		 Less reactive than alkali metals
(e) Formulae of their chlorides $NaCl,KCl,CsCl$ $MgCl_2, CaCl_2, BaCl_2$
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Question 35 Marks
Consider the following elements: Be, Li, Na, Ca, K. Name the elements of (a) same group (b) same period.
Answer
Element At. No. Electronic distribution
Be 4 2, 2
Li 3 2, 1
Na 11 2, 8, 1
Ca 20 2, 8, 8, 2
K 19 2, 8, 8, 1
Same IA group (Li, Na, K) and IIA group (Be, Ca)
In the second period (Be, Li) and in the fourth period (K, Ca).
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Question 45 Marks
The atomic number of an element is more important to the chemist than its relative atomic mass. Why?
Answer
Henry Moseley found that when cathode rays struck anodes of different metals, the wavelength of these metals was found to decrease in a regular manner of changing the metal of anode in the order of its position in the periodic table. By this, he concluded that the number of positive charges present in the nucleus due to protons (atomic number) is the most fundamental property of the element.
So, Henry Moseley found that the atomic number is a better fundamental property of an element compared to its atomic mass. This lead to the modern periodic law.
This law gave explanations for anomalies in Mendeleev's classification of elements such as
  • The position of isotopes with the same atomic number can be put in one place in the same group.
  • Position of argon and potassium: Potassium with a higher atomic number should come later, and argon with a lower atomic number should come first.
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