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Question
Based on the group valency of element write the molecular formula of the following compound giving justification:
Compound formed when an element A of group 2 combines with an element B of group seventeen.
Solution
The general formula for those kinds of compounds would be AB2
Example- MgCl2, CaCl2. This is because the valency of group 2 elements is 2 and that of group 17th elements if 1 so to satisfy the combining capacity of group 2 elements two of group 17 elements are required in the molecular formula. 
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RELATED QUESTIONS
Given below are some elements of the modern periodic table. Atomic number of the element is given in parentheses.
A(4), B(9), C(14), D(19), E(20)
(a) Select the element that has one electron in the outermost shell. Also, write the electronic configuration of this element.
(b) Which two elements amongst these belong to the same group? Give reasons for your answer.
(c) Which two elements amongst these belong to the same period? Which one of the two has bigger atomic radius?
Calcium is an element with atomic number 20. Stating reason, answer each of the following questions:-
(i) Is calcium a metal or a non-metal?
(ii) Will its atomic radius be larger or smaller than that of potassium with atomic number 19?
(iii) Write the formula of its oxide.
Define the term : Valency
An element X belongs to group 2 and another element Y belongs to group 15 of the periodic table:
(a) What is the number of valence electron in X?
(b) What is the valency of X?
(c) What is the number of valence electrons in Y?
(d) What is the valency of Y?
Explain how you have arrived at your answers.
The atomic number of an element is 20. In modern periodic table, this element is placed:
(a) 2nd period
(b) 4th period
(c) 3rd period
(d) 1st period
Which of the following element does not lose an electron easily?
(a) Na
(b) F
(c) Mg
(d) Al
An element X belong to 3rd periods and group II of the periodic table state:
the number of valence electrons,
What will be the valency of an element of atomic number 9 (nine)?
K, Pb, Ca, Zn (In the increasing order of the reactivity)
The elements of one short period of the periodic table are given below in order from left to right:
| Li | Be | B | C | O | F | Ne |
Place the three elements fluorine, beryllium and nitrogen in the order of increasing electronegativity.
