# Frank Solutions for Chapter 8 The Periodic Table Class 9 Chemistry ICSE

1. What is meant by the term ‘group’ in the context of the periodic table?

The present form of periodic table has eighteen vertical columns called ‘groups’. These groups are numbered from 1 to 18.

2. What are periods?

Seven horizontal rows in periodic table are called periods. These are numbered as 1, 2, 3, 4, 5,6 and 7 from top to bottom.

3. What are Dobereiner's law of triad? Give one example of a Dobereiner's triad.

Certain chemically similar elements are arranged into set of three elements are called triads. When these elements are arranged in order of their atomic mass, the atomic mass of the middle element is approximately average of the atomic masses of the other two.

For Example - Lithium, Sodium, Potassium

4. A, B and C are the three elements of a Dobereiner's triad. If the atomic weight of A is 40 and that of C is 137, calculate the atomic mass of B.

According to Dobereiner’s law of Triad,

When certain elements are arranged in order of their atomic mass, the atomic mass of the middle element is approximately average of the atomic masses of the other two.

i.e., (A + C)/2 = B

= (40 + 137)/2

= 88.5

5. (a) What is Newland’s law of octaves ?

(b) What was its basis ?

(c) Was the law of octaves valid beyond calcium?

(d) A and B are two elements obeying Newland’s law. How many elements are there in between A and B?

(a) When elements are arranged in increasing order of their atomic masses, the eighth element resembles the first in physical and chemical properties just like the eighth note on a musical scale resembles the first note.

(b) It is based on the notes of the musical scale. x

(c) No, the law of octaves was not valid beyond calcium i.e. not valid for heavier elements having atomic no. greater than ‘40’.

(d) There are 6 elements in between A and B.

6. Give important conclusions by Newland's law of octaves.

Important conclusions of Newland’s law of octaves are –

1. It was the first logical attempt to classify elements on the basis of atomic masses.
2. Periodicity of elements was recognized for the first time.

7. State the Mendeleev's periodic law.

The physical and chemical properties of elements are the periodic functions of their atomic masses.

8. What was the need for classification of elements?

1. It helps to understand that the properties of elements are related with some fundamental unit of all elements.
2. It simplifies and systemizes the study of the properties of various elements and their compounds.
3. It helps to understand the relationship between the different types of elements.
4. It helps to understand the cause of gradual change in properties from one element to another.

9. State the number of elements in period 1, period 2 and period 3 of the periodic table.

The number of elements in various periods are-

1. Period 1-2
2. Period 2-8
3. Period 3-8

10. Name the elements of period 1.

Hydrogen and Helium are the elements of period 1.

11. What is the common feature of the electronic configurations of the elements at the end of period 2 and period 3?

At the end of the period 2 and period 3 the outer shell of the elements are fully filled i.e., they have complete octet.

12. If an element is in group II (2), is it likely 10 be metallic or non-metallic in character.

The element of group II (2) is likely to be metallic in character.

13. Within a group, where would you expect to find the element with greatest metallic character.

Metallic character increases on moving down the group. Therefore, the element that is placed at the end of the group will have the greatest metallic character.

14. Name the following:

(a) Two alkali metals and their groups and period.

(b) Two alkaline earth metals with their groups and periods.

(c) The group to which halogens belong.

(d) Elements of groups from 3 to 12.

(e) Noble gas with duplet arrangement of electrons.

(f) A metalloid of group 14.

(g) The bond formed between the atoms of an element of group 2 and group 16.

(h) The bond formed between the atoms an element of group 14 and group 17.

(i) Pair of elements showing a diagonal relationship.

(j) A group in which all gases are present.

(a) Two alkali metals and their groups and period are-

Lithium - First group and second period.

Sodium - First group and third period.

(b) Two alkaline earth metals with their groups and periods are-

Beryllium - Second group and Second period

Magnesium - Second group and Third period

(c) Halogens belong to Group 17.

(d) Elements of groups from 3 to 12 are called as transition elements.

(e) Helium gas has duplet arrangement of electrons.

(f) Germanium is a metalloid of group 14.

(g) The bond formed between the atoms of an element of group 2 and group 16 is called as electrovalent or ionic bond.

(h) The bond formed between the atoms an element of group 14 and group 17 is called as covalent bond.

(i) Lithium and Magnesium are the elements which are showing a diagonal relationship.

(j) In Group 18 all elements are gases.

15. Fill in the blanks:

(a) The name of scientist who is related to the musical notes with classification of elements is ____ and his law is known as ____.

(b) The _____ of elements was the basis of Mendeleev's classification.

(c) There are _____ groups and ____ periods in the present form of periodic table.

(d) Elements having outermost shell incomplete are called ___.

(e) Modern periodic law is based on ___ and was proposed by ___.

(f) Periodicity is due to repetition of ___.

(9) Moving across the period non-metallic character __.

(h) An atom of a group 2 element has ___in its valence shell.

(i) All the elements of a period have ___ valency.

(a) Newland, Newland law of Octaves

(b) atomic masses

(c) 18, 7

(d) unstable

(e) Atomic number, Moseley

(f) similar outer electronic configuration at certain regular intervals

(g) decreases

(h) 2 electrons

(i) different

16. State whether the following statements are true or false.

(a) Mendeleev's periodic law was based on atomic number.

(b) Zero group was not present in the Mendeleev's periodic table.

(c) Every period of periodic table begins with alkali metal.

(d) Similar electronic configuration is repeated after intervals of 2, 8, 8, 18 and 32 in long form of periodic table.

(e) Non-metals form ionic bonds among themselves.

(f) In modern periodic table isotopes of an element are placed at different places.

(g) In going down the group, metallic character may increase or decrease.

(a) False

(b) True

(c) True

(d) False

(e) False

(f) False

(g) False

17. Five elements A, B, C, D and E have atomic number 3, 5, 12, 18, 20 respectively. Answer the following questions related with them.

(a) Write their electronic configurations.

(b) Which element is placed right to A.

(c) Which element belongs to same group.

(d) Write the formula for sulphate of C.

(e) Which has a smaller size atom C or E.

(f} Name the element placed below A.

(g) Name the first element of the group to which D belongs.

(h) Write the formula for chloride of B.

(i) Write the formula for oxide of A.

(j) Name another non-metallic element which belongs to the same period as A.

(a) A - 2, 1

B - 2, 3

C-2, 8, 2

D-2, 8, 8

E - 2, 8, 8, 2

(b) B is placed right to A.

(c) C and E belongs to same group.

(d) The formula for sulphate of C is CSO4.

(e) C has a smaller size atom.

(f} Sodium is placed below A.

(g) Helium is the first element of the group to which D belongs.

(h) The formula for chloride of B is BCl3.

(i) A2O is the formula of oxide of A.

(j) Fluorine is the non-metallic element which belongs to the same period as A.

18. (a) Name an element whose properties were predicted on the basis of its position in Mendeleev's periodic table.

(b) Name two elements whose atomic weights were corrected on the basis of their positions in Mendeleev's periodic table.

(c) How many elements were known at the time of Mendeleev's classification of elements.

(a) Properties of Germanium i.e. also called as eka-silicon were predicted on the basis of its position in Mendeleev's periodic table.

(b) Beryllium and Gold are the two elements whose atomic weights were corrected on the basis of their positions in Mendeleev's periodic table.

(c) There were 63 elements known at the time of Mendeleev's classification of elements.

19. State the merits of Mendeleev’s classification of elements.

Merits of Mendeleev's classification of elements are:-

1. Systematic study of the element: Elements could now be studied as groups or families rather than individuals. The Mendeleev's periodic table simplified and systemized the study of the elements and their compounds.
2. Prediction of new elements: While arranging the elements, in increasing order of atomic mass, Mendeleev left some blanks for the elements that were not discovered at that time.
Though unknown, he was able to predict their properties more or less accurately. He named 3 of such elements as Eka-boron was later named as scandium, Eka-aluminium as gallium and eka-silicon. He named them, as they were below boron, aluminium and silicon in the respective sub-groups. Eka-boron was later named as scandium, eka-aluminium as gallium and eka-silicon as germanium.
3. Correction of atomic masses: The Mendeleev's periodic table helped in correcting the atomic masses of elements based on their position in periodic table. Example-Atomic masses of Be was corrected from 13.5 to 9.

20. Why did Mendeleev leave some gaps in his periodic table of elements? Explain your answer with an example.

Mendeleev left some gaps in his periodic table of elements for the elements that were not discovered at that time. Though they were unknown, he was able to predict their properties more or less accurately at that time.

Example - He named eka-boron, eka- aluminium and eka-silicon to some elements as they were just below boron, aluminium and silicon in the respective sub-groups. Eka-boron was later named as scandium, eka-aluminium as gallium and eka-silicon as germanium.

21. What is the main characteristic of the last elements in the periods of the periodic table? What is the general name of such elements?

The main characteristic of the last elements in the periodic table are-

1. Their octet is attained.
2. They are inert in nature.
3. The general name of such elements is noble gas or inert elements.

22. (a) State the modern periodic law.

(b) How many periods and groups are there in the long form of the periodic table?

(c) What is the number of elements in each period?

(a) The physical and chemical properties of elements are the periodic functions of their atomic numbers.

(b) There are 7 periods and 18 groups in the long form of the periodic table.

(c) The number of elements in each period is-

• 1 period-2
• 2 period-8
• 3 period-8
• 4 period-18
• 5 period-18
• 6 period-32
• 7 period-Incomplete

23. The electronic configuration of an element X is 2, 8, 7.

(a) What is the group number of X?

(b) What is the period number of X?

(c) How many valence electrons are there in an atom of X?

(d) What is the valency of X?

(e) Is it a metal or non-metal?

(f) Name the element right and left to it.

(g) What will be the atomic number of the elements above and below it in the periadic table?

(a) X belongs to 17th group.

(b) The period number of X is 3.

(c) In atom of X there are 7 valence electrons.

(d) Valency of X is 1.

(e) It is non-metal.

(f) The element right to it is Argon and the element left to it is Sulphur.

(g) The atomic number of the elements above to it is 9 and below to it is 35 in the periodic table.

24. (a) Elements X and Y belong to group 1 and 17 of the periodic table respectively. What will be the nature of bond in the compound XY?

(b) The elements X, ¥ and Z belong to group 2, 14 and 16 respectively of the periodic table:

(i) Which two elements will form covalent bond?

(ii) Which two elements will form ionic bond?

(a) The nature of bond will be ionic in the compound XY.

(b) (i) Y and Z will form covalent bond.

(ii) X and Z will form ionic compound.

25. An element X combines with oxygen to form an oxide ionic XO.

(a) How many electrons would be there in the outermost shell of the element X?

(b) To which group of the periodic table does the element X belong?

(c) Write the formula of the compound formed when X reacts with chlorine.