Read the given passage and answer any four questions from (a) to (e).
Metallic Character: The ability of an atom to donate electrons and form a positive ion (cation) is known as electro-positivity or metallic character. Down the group, metallic character increases due to increase in atomic size and across the period, from left to right electropositivity decreases due to decrease in atomic size.
Non-Metallic Character: The ability of an atom to accept electrons to form a negative ion (anion) is called non-metallic character or electronegativity. The elements having high electro-negativity have a higher tendency to gain electrons and form anion. Down the group, electronegativity decreases due to increase in atomic size and across the period, from left to right electro -negativity increases due to decrease in atomic size.
(a) Which of the following correctly represents the decreasing order of metallic character of Alkali metals plotted in the graph?
(i) Cs>Rb>Li>Na>K
(ii) K>Rb>Li>Na>Cs
(iii) Cs>Rb>K>Na>Li
(iv) Cs>K>Rb>Na>Li
Answer
As we go down the group , atomic size increases and the ability to donate electrons, i.e. electropositivity increases . So, the metallic character also increases.
The order of increasing atomic size is as follows: Cs>Rb>K>Na>Li
So, the correct option is (iii)
(b) Hydrogen is placed along with Alkali metals in the modern periodic table though it shows nonmetallic character:
(i) as Hydrogen has one electron & readily loses electrons to form negative ions.
(ii) as Hydrogen can easily lose one electron like alkali metals to form a positive ion.
(iii) as Hydrogen can gain one electron easily like Halogens to form a negative ion.
(iv) as Hydrogen shows the properties of nonmetals.
Answer
Alkali metals lose one electron to form a positive ion.
Hydrogen also loses its one electron to form H +
So, the correct answer is (ii)
(c) Which of the following has the highest electronegativity?
(i) F
(ii) Cl
(iii) Br
(iv) I
Answer
- Electronegativity decreases as we go down the group.
- The order of electronegativity can be given as: F>Cl>Br>I
So, the correct answer is (i)
(d) Identify the reason for the gradual change in electronegativity in halogens down the group.
(i) Electronegativity increases down the group due to decrease in atomic size.
(ii) Electronegativity decreases down the group due to decrease in tendency to lose electrons.
(iii) Electronegativity decreases down the group due to increase in atomic radius/ tendency to gain electron decreases.
(iv) Electronegativity increases down the group due to increase in forces of attractions between nucleus & valence electrons.
Answer
- Electronegativity decreases down the group due to an increase in atomic radius.
- It leads to a decrease in the force of attraction between valence electrons and nucleus.
- So, the tendency to gain electrons decreases .
So, the correct answer is (III)
(e) Which of the following reasons correctly justifies that “Fluorine (72pm) has a smaller atomic radius than Lithium (152pm)”?
(i) F and Li are in the same group. Atomic size increases down the group
(ii) F and Li are in the same period. Atomic size increases across the period due to increase in number of shells
(iii) F and Li are in the same group. Atomic size decreases down the group
(iv) F and Li are in the same period and across the period atomic size/radius decreases from left to right.
Answer
- F and Li are in the same period
- Atomic size/radius decreases from left to right.
So, the correct answer is (III)
