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

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

Topic 5.1 Making order out of chaos - Early attempts at the classification of elements

Q.1. Did Döbereiner’s triads also exist in the columns of Newlands’ Octaves? Compare and find out.

Answer:

Yes, Dobereiner's triads also exist in the column of Newland's octaves.

Newland's law of octaves, says that every eight elements had properties similar to that of the first.

For example, the element Lithium, sodium, and potassium are present in the second column of Newland's classification of elements. If lithium is the first element then, the sodium will be the 8th element and considering again sodium as the 1st element, then the 8th element will be potassium.

So, that means according to Newland's Law of octaves, lithium, sodium, and potassium should have similar properties and also these elements form a Dobereiner's traid having similar chemical properties.

Q.2. What were the limitations of Döbereiner’s classification?

Answer:

The limitation of Doberenier's classification:

Döbereiner could identify only three triads from the elements known at that time. Hence, this system of classification into triads was not found to be useful.

Q.3. What were the limitations of Newlands’ Law of Octaves?

Answer :

The limitations of Newland's law of octaves are:

(1) It was found that the Law of Octaves was applicable only up to calcium, as after calcium every eighth element did not possess properties similar to that of the first.

(2) It was assumed by Newlands that only 56 elements existed in nature and no more elements would be discovered in the future. But, later on, several new elements were discovered, whose properties did not fit into the Law of Octaves.

(3) Newland put two elements together in one slot and that too in the column of unlike elements having different properties.

Example: Cobalt and Nickel were put together in just one slot and that too in the column of elements like fluorine, chlorine, and bromine which were very different properties from these elements.

CBSE NCERT solutions for class 10 science chapter 5 Periodic Classification of Elements

Topic 5.2 Making order out of chaos: Mendeléev’s Periodic Table

Q.1. (a) Use Mendeléev’s Periodic Table to predict the formulae for the oxides of the element:

• K

Answer:

The general formula for the oxides of the element Potassium (K): Potassium belongs to the group I of Mendeleev's periodic table, Hence, the formula of its oxide will be

Q.1. (b) Use Mendeléev’s Periodic Table to predict the formulae for th e oxides of the element:

• C

Answer:

The general formula for the oxides of the element Carbon (C): Carbon belongs to the group IV of Mendeleev's periodic table,

Hence, the formula of its oxide will be

Q.1. (c) Use Mendeléev’s Periodic Table to predict the formulae for the oxides of the element :

• Al

Answer:

The general formula for the oxides of the element Aluminium (Al): Aluminum belongs to the group III of Mendeleev's periodic table,

Hence, the formula of its oxide will be

Q.1. (d) Use Mendeléev’s Periodic Table to predict the formulae for the oxides of the following elements:

• Si

Answer:

The general formula for the oxides of the element Silicon (Si): Silicon belongs to the group IV of Mendeleev's periodic table,

Hence, the formula of its oxide will be

Q.1. (e) Use Mendeléev’s Periodic Table to predict the formulae for the oxides of the element:

• Ba

Answer:

The general formula for the oxides of the element Barium (Ba): Barium belongs to the group II of Mendeleev's periodic table,

Hence, the formula of its oxide will be

Q.2. Besides gallium, which other elements have since been discovered that were left by Mendeléev in his Periodic Table? (any two)

Answer:

Besides gallium Scandium (Sc) and Germanium (Ge) elements have been discovered for which gaps were left by Mendeleev in his periodic table.

Q.3. What were the criteria used by Mendeléev in creating his Periodic Table?

Answer:

The criteria used by Mendeleev in creating his periodic table were:

(i) The atomic mass of the elements was used to arrange the elements.

(ii) Grouping the elements according to their similar chemical properties.

And hence proposed that the chemical properties of the elements are the periodic function of their atomic masses and thus he arranged the elements according to the increasing order of atomic masses.

Q.4. Why do you think the noble gases are placed in a separate group?

Answer:

Noble gases are inert nature elements. In the periodic table, they are placed in a separate group because they have a unique property and are very different from other elements.

NCERT solutions for class 10 science chapter 5 Periodic Classification of Elements

Topic 5.3: Making order out of chaos: The Modern Periodic Table

Q.1. How could the Modern Periodic Table remove various anomalies of Mendeléev’s Periodic Table?

Answer:

Modern periodic table removes, various anomalies of Mendeleev's periodic table as follows:

(1) In the modern periodic table, elements are arranged in the increasing order of their atomic number, not in the atomic mass.

(2) In the modern periodic table, the isotopes are placed in the same place as they having the same atomic number but different atomic masses.

(3) Now, the same group elements have the same number of valence electrons.

(4) Hydrogen is now placed in the group containing the same valence electrons.

Q.2. Name two elements you would expect to show chemical reactions similar to magnesium. What is the basis for your choice?

Answer:

Elements that show similar chemical reactions are Beryllium (Be) and Calcium (Ca) because they belong to the same group. i.e., group 2nd in the modern periodic table

Q.3. (a) Name

• Three elements that have a single electron in their outermost shells.

Answer:

Single valence electron elements are: (a) Lithium, Sodium, and Potassium .

Q.3.(b) Name

• Two elements that have two electrons in their outermost shells.

Answer:

Magnesium and Calcium have two electrons in their outermost shells.

Q.3. (c) Name

• Three elements with filled outermost shells.

Answer:

The elements which have fully filled outermost shells are noble gases.

Example: Helium, Neon, and Argon.

Q.4. (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?

Answer:

Yes , they have the following similar properties:

(1) Belongs to the same group I in the periodic table.

(2) Have 1 valence electron in the valence shell.

(3) All are alkali metals.

(4) They are highly reactive.

Q.4. (b) Helium is an unreactive gas and neon is a gas of extremely low reactivity. What, if anything, do their atoms have in common?

Answer:

Both Helium and Neon are noble gases which belong to the zero groups in the modern periodic table. They have fully filled the outermost shell with electrons. Helium has two electrons in its K shell whereas Neon has 8 electrons in its outermost shell.

Q.5. In the Modern Periodic Table, which are the metals among the first ten elements?

Answer:

Among the first ten elements metals are only 2 elements:

Lithium (Li) and Beryllium (Be) .

Q.6. By considering their position in the Periodic Table, which one of the following elements would you expect to have maximum metallic characteristics?

Answer:

The metallic character of the elements decreases as we move horizontally from left to right in the periodic table.

Therefore, Be will have the maximum metallic character because of its extreme left position in the periodic table.

NCERT solutions for class 10 science chapter 5 Periodic classification of elements- Exercise solutions

Q.1. 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.

(a) The elements become less metallic in nature.
(b) The number of valence electrons increases.
(c) The atoms lose their electrons more easily.
(d) The oxides become more acidic.

Answer:

When going from left to right across the periods of the periodic table, the number of valence electrons increases. So, the tendency to lose electrons decreases whereas to accept electron increases.

Hence the option (C) is incorrect.

Q.2. Element X forms a chloride with the formula , which is solid with a high melting point. X would most likely be in the same group of the Periodic Table as

Answer :

X must be Magnesium (Mg) which has a valency of 2 and when it combines with chlorine having valency 1, it forms .

Hence, the option (B) is correct.

Q.3.(a) Which element has

• two shells, both of which are completely filled with electrons?

Answer:

The element which has two shells, which are both completely filled with electrons is,

Neon with electronic configuration .

Q.3.(b) Which element has

• The electronic configuration 2, 8, 2?

Answer:

The given electronic configuration is of Magnesium (Mg).

Q.3. (c) Which element has

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

Answer:

The element having three shells and four electrons in its valence shell is Silicon (Si) .

Q.3. (d) Which element has

• A total of two shells, with three electrons in its valence shell?

Answer:

The element having two shells and three electrons in its valence shell is Boron (B) .

Q.3. (e) Which element has

• Twice as many electrons in its second shell as in its first shell?

Answer:

The element having twice as many electrons in its second shell as in its first shell will be:

Carbon with electronic configuration:

Q.4. (a) What property do all elements in the same column of the Periodic Table as boron have in common?

Answer:

The same column of the periodic table as boron belongs to the group 13th has 3 valence electrons,

Hence, its valency is 3.

Therefore, all the elements in the same column of the periodic table as Boron will have a valency of 3.

Q.4. (b) What property do all elements in the same column of the Periodic Table as fluorine have in common?

Answer:

Fluorine belongs to the group 17th in the periodic table and having 1 valence electron.

Hence its valency is 1.

Therefore, all elements in the same column of the periodic table as fluorine will have a valency of 1.

Q.5. An atom has electronic configurations 2, 8, and 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)

Answer:

The electronic configuration: is of Chlorine.

(a) The atomic number of this element will be: .

(b) It will be chemically similar to the element Fluorine (9) as it also has the same number of valence electrons in its valence shell.

Q.6. (a) The position of three elements A, B and C in the Periodic Table are shown below–

• State whether A is a metal or non-metal.

Answer:

As we know in the periodic table, group 3 - group 12 are transition metals and group 13 to group 16 are metalloids and then there are halogens in 17 groups.

A is in group 17 so it is a non-metal.

Q.6.(b) The position of three elements A, B, and C in the Periodic Table are shown below –

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

Answer:

Element C is less reactive than A because in the halogens the reactivity decreases as we move down. This happens because as we move down the nuclear attraction increases due to an increase in atomic mass. Stronger attraction toward electron will make it harder to react with any other element that's why they are less reactive.

Q.6.(c) The position of three elements A, B and C in the Periodic Table are shown below –

Will C be larger or smaller in size than B?

Answer:

C is much smaller than the size of the B because C has a higher atomic mass which means higher attraction to the electron which means compact (less) size.

Q.6. (d) The position of three elements A, B ,and C in the Periodic Table are shown below –

• State whether A is a metal or non-metal.
• Which type of ion, cation or anion, will be formed by element A?

Answer:

A will form an anion as it accepts an electron to complete its octet.

Q.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 element Nitrogen (N) is .

The electronic configuration of the element phosphorus (P) is

So, Nitrogen will be more electronegative than Phosphorus because its atom has a small size due to which the attraction of its nucleus for the incoming electron is more.

Q.8. How does the electronic configuration of an element relate to its position in the Modern Periodic Table?

Answer:

The electronic configuration of an element gives the distribution of electrons in various shells present in the element. The atoms with similar electronic configuration are placed in the same column, hence groups have the same number of valence electrons.

Group number can be known by knowing the number of valence electrons.

The number of shells present in an element is equal to the period number.

Thus, the information of electronic configuration is enough to know the group and period number of an element.

Q.9. 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:

Element with atomic no. 12 and atomic no. 38 will have chemical properties the same as calcium. this is due to the fact that they have valency the same as calcium and also lie in the same group.

Q.10. Compare and contrast the arrangement of elements in Mendeléev’s Periodic Table and the Modern Periodic Table.

Answer: