 Periodic Classification of Elements class 10 science NCERT exercise solution

# Periodic Classification

## NCERT Solution

Which element has

1. Two shells, both of which are completely filled with electrons?

2. The electronic configuration 2, 8, 2?

3. A total of three shells, with four electrons in its valence shell?

Answer: Si (Silicon) (14): 2, 8, 4
4. A total of two shells, with three electrons in its valence shell?

Answer: B (Boron) (5): 2, 3

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.

1. The elements become less metallic in nature.
2. The number of valence electrons increases.
3. The atoms lose their electrons more easily.
4. The oxides become more acidic.

Answer: (c) The atoms lose their electrons more easily

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

1. Na
2. Mg
3. Al
4. Si

What property do all elements in the same column of the Periodic Table as boron have in common?

Answer: Boron is metalloid while all other elements in the same column of the Periodic Table are metals, thus metallic character is common in the same column of the periodic table as boron have.

What property do all elements in the same column of the Periodic Table as fluorine have in common?

Answer: All elements belong to same column as fluorine, are non-metals and are highly electronegative in character. All of them have valence electrons equal to seven, and thus can accept one electron to complete their octet.

An atom has electronic configuration 2, 8, 7.

1. What is the atomic number of this element?

Anwer: 17
2. 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)

Anwer: F (9) Fluorine (As fluorine has valence electron equal to seven)

The position of three elements A, B and C in the Periodic Table are shown below

Group 16 Group 17
A
B C
1. State whether A is a metal or non-metal.

2. State whether C is more reactive or less reactive than A.

3. Will C be larger or smaller in size than B?

4. 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 configuration of these two elements. Which of these will be more electronegative? Why?

Phosphorus (15): 2, 8, 5

Since, electronegativity decreases with moving from top to bottom in a group, thus Nitrogen will be more electronegative.

How does the electronic configuration of an atom relate to its position in the Modern Periodic Table?

Answer: Electronic configuration of an element gives the information of valence electrons and number of shell present in the element. We get the information of group number after knowing valence electrons. Number of shells present in an element is equal to period number. Thus, by knowing electronic configuration we know the group number and period number of an element, which is the position of element in periodic table.

In the Modern 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?

Answer: Elements with atomic numbers 12 and 38 have the similar chemical and physical properties of calcium.

Compare and contrast the arrangement of elements in Mendeléev’s Periodic Table and the Modern Periodic Table.

Answer: Comparison of Mendeleev’s Periodic Table and Modern Periodic Table

Mendeleev's Periodic Table Modern Periodic Table
Elements were arranged in increasing order of atomic masses. Elements are arranged in increasing order of atomic numbers.
There are 8 groups. There are 18 groups.
Each group is divided into sub groups a and b. Groups are not divided into sub groups.
Group for noble gases was not present, as noble gases were not discovered at that time. A separate group, i.e. group 18 is present for noble gases.
There was no place for isotopes. This problem was rectified, as slots are determined on the basis of atomic number.