NCERT Solutions for Class 9 Science Chapter 4
Structure of the Atom
NCERT Books for Session 2022-2023
CBSE Board and UP Board
Intext Questions
Page No-52
Questions No-1
How will you find the valency of chlorine, Sulphur and magnesium?
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If the number of electrons in the outermost shell of the atom of an element is less than or equal to
4, then the valency of the element is equal to the number of electrons in the outermost shell.
On the other hand, if the number of electrons in the outermost shell of the atom of an element is greater than 4, then the valency of that element is determined by subtracting the number of electrons in the outermost shell from 8.
The distribution of electrons in chlorine, sulphur, and magnesium atoms are 2, 8, 7; 2, 8, 6 and 2, 8, 2 respectively. Therefore, the number of electrons in the outer most shell of chlorine, sulphur, and magnesium atoms are 7, 6, and 2 respectively.
Thus,
The valency of chlorine = 8 −7 = 1
The valency of sulphur = 8 − 6 = 2
The valency of magnesium = 2
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Here’s how we find the valency of chlorine (Cl), sulfur (S), and magnesium (Mg):
Chlorine (Cl):
– Chlorine belongs to Group 17 (or Group VIIA) of the periodic table.
– It has 7 electrons in its outer shell (2s² 2p⁶ 3s² 3p⁵).
– To achieve a stable electron configuration like the noble gas neon (with 8 electrons in its outer shell), chlorine tends to gain 1 electron.
– Therefore, the valency of chlorine is -1.
Sulfur (S):
– Sulfur is in Group 16 (or Group VIA) of the periodic table.
– It has 6 electrons in its outer shell (2s² 2p⁶ 3s² 3p⁴).
– Sulfur needs 2 more electrons to achieve a stable electron configuration, similar to the noble gas argon (with 8 electrons in its outer shell).
– Thus, the valency of sulfur is -2.
Magnesium (Mg):
– Magnesium belongs to Group 2 (or Group IIA) of the periodic table.
– It has 2 electrons in its outer shell (3s²).
– Magnesium tends to lose these 2 electrons to achieve a stable electron configuration, akin to the noble gas neon (with 8 electrons in its outer shell).
– Hence, the valency of magnesium is +2.
Valency signifies the combining capacity of an element based on its ability to gain, lose, or share electrons to attain a stable configuration. This understanding helps predict how elements interact and form compounds during chemical reactions.