On the basis of Mendeleev's Periodic Table given below, answer the question that follow the table:
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Besides gallium, which two other elements have since been discovered for which Mendeleev had left gaps in his Periodic Table? Using atomic masses of Li,Na, find the average atomic mass of and compare it with the atomic mass of. State the conclusion drawn from this activity.

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Solution

Gallium and Scandium.
Li Na K
6.939 22.99 39.102
Average atomic mass of $N a = \frac{6.939 + 39.102}{2} = 23.0205$
It is close to 22.99 which is less than actual mass.

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Similar questions

Q. (a) State Mendeleev's periodic law.
(b) What chemical properties of elements were used by Mendeleev in creating his periodic table?
(c) State any three limitations of Mendeleev's classification of elements.
(d) Besides gallium, which two other elements have since been discovered for which Mendeleev had left gaps in his periodic table?
(e) Which group of elements was missing from Mendeleev's original periodic table?

Q. Which of the following statement is correct in regard to the classification of elements?

(a) Elements in modern periodic table are arranged on the basis of increasing atomic masses.
(b) Elements in Mendeleev's periodic table are arranged on the basis of increasing atomic numbers.
(c) In modern periodic table, the element nickel of lower atomic mass is kept before the element cobalt of higher atomic mass.
(d) In modern periodic table, the isotopes of chlorine having different atomic masses are kept in the same group.

Q. Which of these pairs were put by Mendeleev in the wrong order on the basis of increasing atomic mass in his table?

Question 4
Which of the following statement(s) about the Modern Periodic Table are incorrect?

(i) The elements in the Modern Periodic Table are arranged on the basis of their decreasing atomic number

(ii) The elements in the Modern Periodic Table are arranged on the basis of their increasing atomic masses

(iii) Isotopes are placed in adjoining group (s) in the Periodic Table

(iv)The elements in the Modern Periodic Table are arranged on the basis of their increasing atomic number

(a) (i) only
(b) (i), (ii) and (iii)
(c) (i), (ii) and (iv)
(d) (iv) only

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Gallium and Scandium.Li Na K6.939 22.99 39.102Average atomic mass of Na=6.939+39.1022=23.0205It is close to 22.99 which is less than actual mass.

Gallium and Scandium.
Li Na K
6.939 22.99 39.102
Average atomic mass of $N a = \frac{6.939 + 39.102}{2} = 23.0205$
It is close to 22.99 which is less than actual mass.