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Question-1

Did Dobereiner’s triads also exist in the columns of Newlands Octaves? Compare and find out.
Solution:
Yes, Dobereiner’s triads also exist in the columns of Newlands Octaves. For example, the second column of Newlands classification has the elements lithium (Li), sodium (Na) and Potassium (K), which constitute a Dobereiner’s triad.

Question-2

What were the limitations of Dobereiner’s classification?

Solution:
All the known elements could not be arranged in the form of triads. For very low mass or for very high mass elements, the Dobereiner’s triads are not applicable. Take the example of F, Cl and Br. Atomic mass of Cl is not an arithmetic mean of atomic masses of F and Br. As the techniques for measuring atomic masses accurately, improved, the Dobereiner’s triad was unable to remain strictly valid.

Question-3

What were the limitations of Newland’s Law of Octaves?

Solution:
It was not valid for elements that had atomic masses higher than Ca.When more elements were discovered, such as elements from the noble gases such as He, Ne, Ar, they could not be accommodated in his table.

Question-4

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

Solution:
K2O – Potassium Oxide

CaO – Calcium Oxide

Al2O3 – Aluminium Oxide

SiO2 – Silicon dioxide

BaO – Barium Oxide.


Question-5

Besides gallium, which other elements have been left by Mendeleev in his periodic table, since the time they were discovered? (Any two)

Solution:
Scandium and Germanium.

Question-6

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

Solution:
He observed the relationship between the atomic masses of the elements and their physical properties. Among chemical properties, he concentrated on the compounds formed by elements with oxygen and hydrogen.

Question-7

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

Solution:
Due to its inert and low concentration in our atmosphere, they could be placed in a new group without disturbing the existing order.

Question-8

How could the Modern periodic table remove various anomalies of Mendeleev’s periodic table?

Solution:
When the elements are arranged according to their atomic numbers on the basis of modern periodic law, all the anomalies (defects) of Mendeleev’s classification disappear. For example, Position of isotopes: All the isotopes of an element have the same number of protons, so their atomic number is also the same. Since all the isotopes of an element have the same atomic number, they can be put at one place in the same group of the periodic table.

Question-9

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

Solution:
Calcium and Beryllium are the elements that will show chemical reactions similar to magnesium. This is because beryllium and calcium belong to the same group of periodic table as magnesium. All of them have similar electronic configurations with 2 valence electrons each.

Question-10

Name
a. Three elements that have a single electron in their outermost shell.
b. Two elements that have two electrons in their outermost shell.
c. Three elements with filled outermost shell.

Solution:
a. Three elements that have a single electron in their outermost shell are:

1. Lithium

2. Sodium

3. Potassium

b. Two elements that have two electrons in their outermost shell are:

1. Magnesium

2. Calcium

c. Three elements with filled outermost shell are:

1. Argon

2. Helium

3. Neon.


Question-11

a. Lithium, sodium, potassium are metals that react with water to liberate hydrogen. 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?

 

Solution:
a. These elements are alkali metals and they have 1 valence electron in their outermost shell and are therefore very unstable and reactive.

b. These elements each have full outermost subshell, which results in high stability. They only react with other elements in extreme circumstances, the trait for which they are named.

Question-12

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

Solution:
The metals are Lithium and Beryllium.

Question-13

By considering their position in the periodic table, which one of the following elements would you expect to have maximum metallic characteristic?
 
Ga, Ge, As, Se, Be

 

Solution:
Beryllium

Question-14

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

(i) The elements become less metallic in nature

(ii) The number of valence electrons increases
(iii) The atoms lose their electrons more easily
(iv) The oxides become more acidic

 

Solution:
(iii) The atoms lose their electrons more easily – Incorrect statement.

Question-15

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

a. Na            b. Mg             c. Al           d. Si

 

Solution:
b. Mg

Question-16

Which element has?

a.Two shells, both of which are completely filled with electrons?
b. The electronic configuration of 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?

 

Solution:
a. Neon (2,8)

b. Magnesium (2,8,2)

c. Silicon (2,8,4)

d. Boron (2,3)

e. Carbon (2,4)

Question-17

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

Solution:
These elements all have 7 electrons in their outermost shells and these often exist as salts, combined with elements from the Alkali metal group.

Question-18

An atom has electronic configuration 2,8,7.

i. What is the atomic number of this element?
ii. To which of the following elements would it be chemically similar
N (7) F (9) P (15) Ar (18)

 
Solution:
(i) Chlorine – 17

(ii) F (9)

Question-19

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

 

Solution:
A is a non-metal

C is less reactive than A

"C" will be smaller in size than "B" as the atomic size decreases as we go across a period.

Anion will be formed by element A


Question-20

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?

Solution:
Electronic configuration - Nitrogen – 2s2 2p3 and Phosphorus - 1s2 2s2 2p6 3s2 3p3. Nitrogen will be more electronegative; this is because its atom has small size due to which the attraction of its nucleus for the incoming electron is more.

Question-21

How does the electronic configuration of an atom relate to its position in the Modern periodic table?

Solution:
The electronic configuration of an atom increases in the outermost valence shell which relates to its position in the Modern periodic table.

Question-22

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?

Solution:
The atomic number of calcium is 20, so its electronic configuration is 2, 8, 8, 2. Thus, calcium has 2 valence electrons (in its outermost shell). Now, the element which has 2 valence electrons, will have physical and chemical properties resembling to that of calcium. The electronic configuration of element having atomic number 12 is 2, 8, 2. It has 2 valence electrons just like calcium. So, the element having atomic number 12 will have physical and chemical properties resembling that of calcium.

Question-23

Where do you think should hydrogen be placed in the Modern periodic table?

Solution:
Hydrogen element has been placed at the top of group 1, above the alkali metals because the electronic configuration of hydrogen is similar to those of alkali metals.




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