Solution of Chapter 5. Periodic Classification of Elements (NCERT - Science Book)

Did Dobereiner's triads also exist in the columns of Newlands' octaves ? Compare and find out.

What were the limitations of Dobereiner's classification of elements ?

What were the limitations of ' law of octaves ?

Use Mendeleev's periodic table to predict the formulae for the oxides of the following elements : K, C, AI, Si, Ba

Besides gallium, which other elements have since been discovered for which gaps were left by Mendeleev in his periodic table? (any two)

What were the criteria used by Mendeleev in creating his periodic table ?

Why do you think the noble gases are placed in a separate group ?

How could the Modem periodic table remove various anomalies of Mendeleev's periodic table ?

Name two elements you would expect to show chemical reactions similar to magnesium. What is the basis for your choice?

Name:

(a) three elements that have a single electron in their outermost shells.

(b) two elements that have two electrons in their outermost shells.

(c) three elements with filled outermost shells.

(a) Lithium, sodium, potassium are all metals that react with water to liberate hydrogen gas. Is there any similarity in the atoms of these elements ?

(b) Helium is an unreactive gas and neon is a gas of extremely low reactivity. What, if anything, do their atoms have in common ?

In the modem periodic table, which are the metals among the first ten elements ?

By considering their position in the periodic table, which one of the following elements would you expect to have maximum metallic character ?

Ga, Ge, As, Se, Be

Which of the following statements is not a correct statement about the trends when going from left to right across the periods of periodic table ?

Element X forms a chloride with the formula XCl₂ which is a solid with a high melting point. X would most likely be in the same group of the periodic table as :

Which element has :

(a) two shells, both of which are completely filled with electrons ?

(b) the electron configuration 2, 8, 2 ?

(c) a total of three shells, with four electrons in its valence shell ?

(d) a total of two shells, with three electrons in its valence shell ?

(e) twice as many electrons in its second shell as in its first shell ?

What property do all elements in the same column of the periodic table as boron have in common ?

What property do all elements in the same column of the periodic table as fluorine have in common ?

An atom has electronic configuration 2, 8, 7.

(a) What is the atomic number of this element ?

(b) To which of the following elements would it be chemically similar ? (Atomic numbers are given in parentheses)

N (7) F (9) P (15) Ar (18)

The positions of three elements A, B and C in the periodic table are shown below:

(a) State whether A is a metal or non-metal.

(b) State whether C is more reactive or less reactive than A.

(c) Will C be larger or smaller in size than B?

(d) Which type of ion, cation or anion, will be formed by element A ?

Nitrogen (atomic number 7) and phosphorus (atomic number 15) belong to group 15 of the periodic table. Write the electronic configurations of these two elements. Which of these will be more electronegative ? Why?

How does the electronic configuration of an element relate to its position in the modem periodic table ?

In the modem periodic table, calcium (atomic number 20) is surrounded by elements with atomic numbers 12, 19, 21 and 38. Which of these have physical and chemical properties resembling calcium ?

Compare and contrast the arrangement of elements in Mendeleev's periodic table and the Modem periodic table.