NCERT Solutions Class 10 Science Chapter 5: Periodic Classification of Elements

NCERT Solutions of Periodic Classification Of Elements Class 10 Science Chapter 5: These notes might be helpful to students who are looking for the answer to NCERT Science Class 10 Chapter 5. So that students don't have any difficulties when taking notes and reading solutions, the notes, answers, and explanations are presented very straightforwardly. The explanation will provide a concise overview of the theory, which will help with the revising process. Students can save time by using this memo.

NCERT Solutions for Class 10 Science Chapter 5 inside Book Questions

Page Number: 81

Question 1:

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

Answer:

Yes, Dobereiner's triads also existed in Newland's classification of elements.

For Example: If we look at the second column of Newland's classification of elements, then Lithium (Li), Sodium (Na), and Potassium (K) form Dobereiner's triad.

If lithium (Li) is the first element, sodium (Na) would be the eighth element. If Potassium is the eighth element, then sodium will be regarded as the first element.

Question 2:

What were the limitations of Dobereiner's classification?

Answer:

The limitations of Dobereiner's classification of elements were as follows:

1. Dobereiner was only able to find three triads, so it means that he could discover only nine elements then.
2. However, there were more elements apart from which were discovered by Dobereiner.
3. Dobereiner could not classify all the then-known elements in the form of triads.

Question 3:

What were the limitations of Newlands' law of octaves?

Answer:

The limitations of Newlands' law of octaves were as follows:

1. The categorization of elements up to calcium was the only one to which Newlands' law of octaves applied. Every eighth element after calcium lacked the characteristics of the first element.
2. According to Newlands, there were only 56 elements in nature, and no more would ever be found. Later, however, several novel substances whose characteristics did not adhere to Newlands' law of octaves were found.
3. Newlands combined even two elements in one slot, and that too in the column of elements that were unlike each other and had highly dissimilar qualities, to accommodate them into his table.
   In the column of elements like fluorine, chlorine, and bromine, which have completely different qualities from these elements, the two elements, cobalt (Co) and nickel (Ni), were combined in only one slot.
4. Iron (Fe), an element with characteristics similar to cobalt and nickel, was positioned distant from these other elements.

Page Number: 85

Question 1:

Use Mendeleev's Periodic Table to predict the formulae for the oxides of the following elements: K, C, Al, Si, Ba

Answer:

The properties of Metal Oxide are as follows:

1. Metallic oxides have alkaline properties in nature.
2. Most metals combine with oxygen to form metal oxides.
3. In general, the metal reacts in the following way to form respective metal oxides.

Metal + Oxygen → Metal Oxide

The properties of Non-Metallic Oxide are as follows:

1. Non-Metallic oxides generally form when any non-metal reacts with oxygen gas.
2. The non-metallic oxides formed show acidic properties in nature.
3. Generally, a non-metal reacts in the following way to form respective metal oxides.

Non-Metal + Oxygen → Non-Metallic Oxide

Now, by using Mendeleev's Periodic Table, we can write the formula of the oxides of the given elements. The answer will be as follows:

1. At first, we have potassium (K), a metal, forming a basic metallic oxide. It will form Potassium Oxide (K₂O).
2. Secondly, we have Carbon (C) which is a non-metal, so it will form an oxide whose formula will be CO₂.
3. Next, we have Aluminium (Al), a metal, and the oxide formed by this metal is amphoteric oxide. Amphoteric oxide exhibits the properties of acidic oxide and basic oxide. The formula for aluminum oxide is Al₂O₃.
4. The next element we have is Silicon (Si), an element of Group-14, and its oxide formula is SiO2.
5. The Last element we have is Barium (Ba) which belongs to Group-2, and the oxide formula is BaO, i.e., Barium Oxide.

Question 2:

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

Answer:

Apart from Gallium, the two elements discovered were Scandium and Germanium, which were the elements left by Mendeleev in his Periodic Table.

Question 3:

What were the criteria used by Mendeleev in creating his Periodic Table?

Answer:

The criteria used by Mendeleev for creating the Periodic Table were as follows:

1. Mendeleev arranged the elements based on their relative atomic mass in increasing order. Relative atomic mass means weight in grams of the number of atoms present in 12g of carbon-12.
2. He arranged the elements in a tabular form: horizontal rows, Periods, and vertical columns Groups.
3. He formed the table so that elements showing similar properties belonged to the same Group and left spaces for undiscovered elements.
4. Mendeleev arranged the elements based on increasing relative atomic mass because he proposed that the chemical properties of elements are periodic functions of their atomic masses.

Question 4:

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

Answer:

There are various reasons why noble gases are placed in separate groups.

1. Noble gases are very less reactive or almost not reactive when compared to other elements of the periodic table.
2. Noble gases are present in very low concentrations in the atmosphere.
3. Apart from Xenon, no other gases combine with any of the elements of the periodic table.
4. The electronic configuration of the noble gases is fixed (ns²np⁶), so they are kept in a separate group.

NCERT Solutions for Class 10 Science Chapter 5 Inside Book Questions

Page Number: 90

Question 1:

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

Answer:

Modern Periodic Table removed anomalies of Mendeleev's Periodic Table in the following ways:

1. In contrast to Mendeleev's periodic table, which was based on atomic mass, the modern periodic table is based on atomic number.
2. An isotope of an element contains the same number of protons (or atomic number). As a result, they share the same place in the current periodic table.
3. Nickel and cobalt are ranked ninth and tenth, respectively.
4. In the first group of alkali metals, hydrogen is positioned in a distinctive position at the top.

Question 2:

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

Answer:

The chemical properties of the elements can be predicted from the electronic configuration of the elements as it shows the electron distribution of those elements.

Beryllium (Be) and Calcium (Ca) would show similar chemical reactions as magnesium.

Beryllium has an atomic number of 4 while Calcium has an atomic number of 20. Hence, if we look at the electronic configuration of these two elements, they have the same number of electrons in their outermost shell.

Magnesium Electronic Configuration - (2,8,2)

Beryllium Electronic Configuration - (2,2)

Calcium Electronic Configuration - (2,8,8,2)

So we can see that both of these elements have 2 electrons in their valence shell, so they will exhibit similar chemical properties to magnesium because it also has 2 valence electrons.

Question 3:

Name:

1. Three elements that have a single electron in their outermost shells.
2. Two elements that have two electrons in their outermost shells.
3. Three elements with filled outermost shells.

Answer:

a.) Elements that have a single electron in their outermost shells are:

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

c.) Three elements with filled outermost shells are:

Question 4:

1. Lithium, sodium, and potassium are all metals that react with water to liberate hydrogen gas. Is there any similarity in the atoms of these elements?
2. Helium is an unreactive gas and neon is a gas of extremely low reactivity. What, if anything, do their atoms have in common?

Answer:

1. Sodium, potassium, and lithium are all elements of the same group. All three elements, lithium, Sodium, and potassium, contain just one electron in their outermost shells. These all produce alkalies when they react with water.
2. The outermost shells of the helium and neon atoms are filled. While neon's first and second (K and L) shells are fully occupied, helium's first shell is filled. Thus they have no free electrons, so no reaction occurs.

Question 5:

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

Answer:

The first ten elements of the modern periodic table are:

From the Modern Periodic Table, the elements with 1, 2, or 3 valence shell electrons will be regarded as metals. So from the above table, we can conclude that Lithium, Beryllium, and Boron are the metals among the first 10 elements of the modern periodic table.

Question 6:

By considering their position in the Periodic Table, which one of the following elements would you expect to have maximum metallic characteristics?

Ga, Ge, As, Se, Be

Answer:

Among the given elements Gallium (Ga), Germanium (Ge), Arsenic (As), Selenium (Se), and Beryllium (Be), Gallium is the most metallic because it lies on the leftmost side of Period 4 if compared to the above-given elements.

The electron-losing property of an element is based on its position in the modern periodic table. As we move across the table from left to right, the size of the atom decreases because of an increase in nuclear charge.

This means that the element on the leftmost side of the periodic table will have the greater atomic size with the least nuclear charge, and the elements can easily lose electrons and thus can show more metallic character. As Gallium is located to the leftmost so it has maximum metallic character.

NCERT Solutions for Class 10 Science Chapter 5 Exercise QuestionsM

Question 1:

Which of the following statements is not a correct statement about the trends while going from left to right across the periods of the 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.

Electrons losing the property of an element decrease, if we move from left to right in the periodic table. This is because the increase in nuclear charge reduces the atom's size and holds the electrons with a strong nuclear force, making it difficult for an element to lose electrons.

Question 2:

Element X forms a chloride with the formula XCl₂, which is 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

Answer:

b.) Mg

As the question says, it forms a chloride with the formula XCl2, so element X needs to donate 2 electrons to Cl. Here only Mg is the element with 2 electrons and forms MgCl₂ with chlorine.

Sodium has 1 electron in its outermost shell to form NaCl, Aluminium has 3, which will form AlCl₃ and Silver has 4, which will form SiCl₄.

Question 3:

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?
4. a total of two shells with three electrons in its valence shell?
5. twice as many electrons in its second shell as in its first shell?

Answer:

1. Element that has two shells and both of which are filled with electrons is Neon and its electronic configuration is (2, 8).
2. Atomic number is 12; hence Magnesium lies at the 12th number.
3. Element with three shells and four electrons in the valence shell is Silicon, and its electronic configuration is (2, 8, 4).
4. Boron (2, 3)
5. Carbon (2, 4)

Question 4:

1. What properties do all elements in the same column of the Periodic Table as boron have in common?
2. What properties do all elements have in the same column of the Periodic Table? As fluorine have in common?

Answer:

1. Electronic Configuration of Boron is (2, 3). So elements with a valency of three and three valence electrons will be in the same column or group as boron.
2. Electronic Configuration of Fluorine is (2, 7). So elements with seven electrons in their outermost shells and a valency of one will form acidic oxides when they are in the same column or group as fluorine.

Question 5:

An atom has electronic configuration 2, 8, 7.

1. What is the atomic number of this element?
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)

Answer:

1. The atomic number of the given element is 2 + 8 + 7 = 17.
2. Due to its electronic arrangement of 2,8, 7, it would have chemical properties like fluorine because fluorine has 7 electrons in its valence shell. The electronic configuration of Fluorine is (2, 7), and its atomic number is 9.

Question 6:

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?

Answer:

1. A is a non-metal since group 17's valency is 7, and all of these elements accept electrons. On the other hand, metals are electron donors.
2. Non-metals get more non-reactive as we move down in a group. Therefore C is less reactive than A. They get less reactive because the size of the atom increases and the nuclear charge decreases.
3. Because B and C belong to the same period and size reduces as one proceeds from left to right, C is smaller than B.
4. Because A is a non-metal, it will produce an anion.

Question 7:

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?

Answer:

The electronic Configuration of the elements is:

1. Nitrogen - (2,5)
2. Phosphorous - (2, 8, 5)

Because the outermost shell is closer to the nucleus and the nucleus has a stronger magnetic pull on electrons, nitrogen will be more electronegative. The electron-attracting tendency in a periodic table group decreases from top to bottom.

Question 8:

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

Answer:

The basis of the modern periodic table is the atomic number, which is directly connected to the electronic configuration. So an element's group number and period number can be identified from its electronic configuration. For instance, an element would fall under group 1 or group 2 if its outermost shell had one or two electrons.

The alkali metals are all assigned to group 1 because they all have one electron in their outermost shell. As a result, the outermost shell of all group two elements has two electrons. There are 5 electrons in the outermost shell of group 15 elements. Similarly, an element's number of shells determines its period number. For instance, magnesium has an atomic number of 12, and its electronic structure is 2, 8, 2. So, it is an element of the third period.

Question 9:

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

Answer:

The electronic configuration of elements are:

The physical and chemical characteristics of magnesium (Mg), which has an atomic number of 12, and strontium (Sr), which has an atomic number of 38, will exhibit similar chemical and physical properties as calcium, which has an atomic number of 20 because both of them have same valence electrons as calcium.

Question 10:

Compare and contrast the arrangement of elements in Mendeleev's Periodic Table and the Modern Periodic Table.