(a) Explain why, the first period of the modern periodic table has only two elements whereas second period has eight elements
(b) Why do elements in the same group show similar properties but the elements in different groups show different properties ?
(c) For each of the following triads, name the element with the characteristics specified below :
(d) State one reason for keeping fluorine and chlorine in the same group of the periodic table.
(e) What are the merits of the modern periodic table of elements ?
Lakhmir Singh Chemistry Class 10
Answers
Here is your answer !
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a) The 1st period has two elements because the 1st electron shell of an atom c a n take a maximum of two electrons only. The 2nd period of the periodic table has 8 electrons because the maximum no. of electrons which can be put in the 2nd shell of an atom is 8.
(b) The elements in the same group show similar properties because they have similar electronic configuration (having the same number of valence electrons) whereas the elements of different groups have different electronic configurations (different number of valence electrons) due to which they show different properties.
(c) Incomplete question !
(d) Fluorine and chlorine have been placed in the same group because both of them have 7 valence electrons.
(e) Merits of modern periodic table:
(i) The modern periodic table is based on the atomic numbers of elements which is the most fundamental property of elements.
(ii) It helps us to understand why elements in a group show similar properties but elements in different groups show different properties.
(iii) It explains the reasons for the periodicity in properties of elements.
(iv) It tells us why the properties of elements are repeated after 2, 8, 18 and 32 elements.
Answer:
a.The first period has only two elements because the first shell (K shell) can take a maximum of only two electrons. The second period has eight elements because the second shell (L shell) can accommodate a maximum of 8 electrons. The number of elements in a period depends upon the number of shells
b.elements in the same group have similar properties because they have the same number of valence electrons in their outermost shell. Elements in the same period have different properties because the number of valence electrons in their outermost shells differ.
c.pls check ur question again
d.These elements are in the same group in the periodic table due to their electron configurations:
fluorine: 2, 7
chlorine: 2, 8, 7
They both have 7 electrons in their outer shell, so therefore are both in group 7 of the periodic table, with chlorine directly below fluorine.
e.1. The classification of elements is based on the atomic number, which is a more fundamental property.
2. The reason for placing isotopes at one place is justified as the classification is on the basis of atomic number.
3. It explains the periodicity of the properties of the elements and relates them to their electronic configurations.
4. The position of the elements that were misfits on the basis of mass number (anomalous pairs like argon and potassium) could be justified on the basis of atomic number.
5. The lanthanides and actinides are placed separately at the bottom of theperiodic table.
6. The table is simple, systematic and easy way for remembering the properties of various elements as it is based on the electronic configuration.
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