CBSE Class 10 Science Periodic Classification Of Elements Assignment Set F

Very Short Answer Type Questions :

Question. What would be the nature of oxides formed by the elements on the right side of periodic table?
Answer: On right hand side of the periodic table, most of them are non-metals, therefore they form acidic oxides.

Question. Predict the maximum number of valence electrons possible for atoms in the first period of the periodic table.
Answer: Maximum number of valence electrons in 1st period is 2.

Question. The electronic configuration of two elements X and Y are 2, 8, 7 and 2, 8, 8, 3 respectively. Write the atomic numbers of X and Y.
Answer: X = 2 + 8 + 7 = 17
Y = 2 + 8 + 8 + 3 = 21

Question. Give the number of elements in 2nd and 5th period in the modern periodic table.
Answer: In 2nd period, there are 8 elements.
In 5th period, there are 18 elements.

Question. What is the valency of phosphorus with atomic number 15?
Answer: P(2, 8, 5) has 5 valence electrons, therefore its valency is equal to 3.

Question. Which has larger atomic radius, K(19) or Ca(20)?
Answer: K has larger atomic radius than Ca.

Question. Arrange the following metals in decreasing order of their atomic size:
Ca, Mg, Ba, Be
Answer: Ba > Ca > Mg > Be is the decreasing order of atomic size.

Question. Find the atomic number of the element whose electronic configuration is 2, 8, 5.
Answer: Atomic number = 2 + 8 + 5 = 15.

Question. The formula of magnesium oxide is MgO. State the formula of barium nitrate and barium sulphate, if barium belongs to same group as magnesium.
Answer: The valency of Mg is 2. The valency of Ba is also 2 as they belong to the same group. Formula of Barium nitrate is Ba(NO₃)2, and that of Barium sulphate is BaSO4.

Short Answer Type Questions :

Question. (a) What is meant by periodicity in properties of elements with reference to the periodic table?
(b) Why do all the elements of the same group have similar properties?
(c) How will the tendency to gain electrons change as we go from left to right across a period? Why?
Answer: (a) The repetition of same properties after definite interval is called periodicity in properties.
(b) It is because they have same valence electrons therefore, have similar properties.
(c) Tendency to gain electrons increases from left to right in a period because atomic size goes on decreasing and effective nuclear charge increases.

Question. (a) Why do we classify elements?
(b) What were the two criteria used by Mendeleev in creating his Periodic Table?
(c) Why did Mendeleev leave some gaps in his Periodic Table?
(d) In Mendeleev’s Periodic Table, why was there no mention of Noble gases like Helium, Neon and Argon?
(e) Would you place the two isotopes ‘ of chlorine, CI-35 and CI-37 in different slots because of their different atomic masses or in the same slot because their chemical properties are the same? Justify your answer.
Answer: (a) It is done so as to study the properties of elements conveniently.
(b) Increasing order of atomic mass and similarities in chemical properties (especially nature and formulae of oxide and hydride formed).
(c) These gaps were left for undiscovered elements.
(d) Noble gases were not invented at that time.
(e) They will be kept at same slot as they have same chemical properties.

Question. Name the element with atomic number 19.
a. In which group it is placed?
b. To which period does it belong to?
c. Write its electronic configuration.
Answer: The name of element is Potassium, K(19): 2, 8, 8, 1.
a. It belongs to group 1.
b. It belongs to 4th period.
c. Its electronic configuration is 2,8 8,1.

Question. The atomic number of an element is 20.
a. Write its electronic configuration and determine its valency.
b. Is it a metal or a non-metal?
c. Write formula of its chloride.
d. Is it more or less reactive than Mg(12)? Give reasons for your answer.
Answer: a. Ca(20): 2, 8 8, 2. Its valency is equal to 2.
b. It is a metal.
c. CaCl₂.
d. It is more reactive than Mg due to larger atomic size. It can lose electrons easily due to less effective nuclear charge.

Question. What is periodicity in properties of elements with reference to the Modern Periodic Table? Why do all the elements of the same group have similar properties?
How does the tendency of elements to gain electrons change as we move from left in a period? State the reason of this change.
Answer: The repetition of similar properties after a definite interval is called periodicity of properties.
Tendency to gain electrons increases along a period from left to right because atomic size decreases.

Question. (a) What are ‘groups’ and ‘periods’ in the ‘periodic table’?
(b) Two elements M and N belong to group I and II respectively and are in the same period of the periodic table. How do the following properties of M and N vary?
(i) Sizes of their atoms
(ii) Their metallic characters
(iii) Their valencies in forming oxides
(iv) Molecular formulae of their chlorides
Answer: (a) The vertical columns in the periodic table are called ‘groups’. The horizontal rows in the periodic table are called ‘periods’.
(b) (i) ‘M’ and ‘N’ belong to same period but group I and II. Therefore, ‘N’ will be smaller than ‘M’ as atomic size goes on decreasing from left to right.
(ii) ‘M’ is more metallic than ‘N’. Metallic character goes on decreasing from left to right as tendency to lose electrons decreases due to decrease in atomic size.
(iii) Their valencies are 1 and 2 respectively in forming oxides. Valency goes on increasing first and then decreases.
(iv) MCI, NCI₂ are molecular formulae of their chlorides.

Question. The atomic number of three elements are given below:
A(5), B(7), C(10)
Write the symbol of element which belongs to (a) group 13, (b) group 15 of the periodic table. State the period of periodic table to which these elements belong to. Give reason to your answer.
Answer: a. A(5): 2, 3 belong to group 13 because it has 3 valence electrons.
b. B(7): 2, 5 belong to group 15 because it has 5 valence electrons.
They i.e., A and B belong to second period because they have 2 shells.

Question. (a) How many periods are there in the Modern Periodic Table of elements?
(b) How do atomic radius, valency and metallic character vary down a group?
(c) How do the atomic size and metallic character of elements vary as we move from left to right in a period?
Answer: (a) There are 7 periods.
(b) Atomic radius goes on increasing down the group, valency remains same. Metallic character increases down the group.
(c) Atomic size decreases along a period from left to right. Metallic character decreases along a period from left to right.

Giving reasons, explain the following:
a. Element A is a non-metal.
b. Atoms of element C has a larger size than atoms of element A.
c. Element B has a valency of 1.
Answer: a. A is a non-metal because it can gain one electrons to form anion.
b. C has more number of shells i.e., it has 3 shells because it belongs to 3rd period whereas A has 2 shells as it belongs to 2nd period.
c. B can lose 1 electron to become stable, therefore its valency is equal to 1.

Question. Choose from the following:
4Be,9F,19K,20Ca
(a) The element having one electron in the outermost shell.
(b) Two elements of the same group.
Answer: (a) 19K has one valence electron.
(b) 4Beand 20Cabelong to the same group.

Question. a. Identify the elements among the following which will belong to the same group: H, He, Li, B, C.
b. State the group number of the recognised elements.
c. Name another one element belonging to the same group.
Answer: a. H and Li belong to the same group.
b. They belong to group 1.
c. Na (sodium) also belong to this group.

Question. Examine elements of the third period: Na, Mg, Al, Si, P, S, Cl and Ar Answer the following:
a. Choose (i) Metals, (ii) Non-metals out of these elements.
b. On which side of periodic table we find
(i) metals
(ii) non-metals.
c. Name metalloids out of the elements given above.
Where are they located in the periodic table?
Answer: a. (i) Na, Mg, A1 are metals.
(ii) P, S, Cl, Ar are non-metals.
b. (i) Metals are placed on the left hand side and middle part of the periodic table.
(ii) Non-metals are placed on the right hand side of periodic table.
c. Silicon is a metalloid. They are located between metals and non-metals at the border line in a zigzag manner.

Question. As we move across a period in the periodic table, what is gradation in the following properties: (a) Atomic size, (b) Atomic number, (c) Electronegativity?
Answer: a. Atomic size goes on decreasing across the period from left to right.
b. Atomic number goes on increasing along the period from left to right.
c. Electronegativity goes on increasing along a period from left to right.

Question. Justify the following with suitable reasons:
a. Cations are smaller than the corresponding atoms.
b. Size of atom increases as we move down the group.
c. Atomic size decreases as we move across a period.
Answer: a. Cations are formed by loss of electrons, therefore effective nuclear charge increases, size of atom decreases.
b. It is because number of shells goes on increasing down the group.
c. It is because effective nuclear charge increases along a period.

Question. Given below are some elements of the modern periodic table:
4Be, 9F, 14Si, 19K, 20Ca
a. Select the element that has one electron in the outermost shell and write its electronic configuration.
b. Select two elements that belong to the same group. Give reason for your answer.
c. Select two elements that belong to the same period. Which one of these two has bigger atomic size?
Answer: a. 19K: 2, 8, 8, 1
b. 4Be, 20Ca belong to the same group because both have same number of valence electrons.
Be: 2, 2; Ca: 2, 8, 8, 2
c. 4Be, 9F belong to the same period. 4Be has bigger atomic size than 9F.

Question. a. Predict which of the following will form anions and which will form cations.
(i) Na, (ii) Al, (iii) Cl, (iv) O
b Name two elements that are inert.
Answer: a. Cl and O will form anions i.e., Cl- and O2- Na and A1 will form cations i.e., Na+ and Al3 +.
b. He and Ne are inert elements.

Question. State Mendeleev’s periodic law. Write two achievements of Mendeleev’s periodic table.
Answer: Properties of elements are a periodic function of their atomic mass.
Achievements:
a. It could arrange all the elements discovered at that time.
b. It left some gaps for the elements to be discovered and helped in their discovery by predicting their properties.

Question. Explain the basic character of oxides of elements down the group and across the period.
Answer: Basic character of oxides increases down the group because metallic character increases.
Basic character of oxides decreases along the period from left to right because non¬metallic character increases, metallic character decreases.

Question. An element has atomic number 13.
a. What is the group and period number to which this element belongs to?
b. Is the element a metal or a non-metal? 
Answer: a. It belongs to group 13, 3rd period because it has 3 valence electrons and 3 shells.
b. It is a metal because it can lose 3 electrons to become stable.

Question. Atoms of seven elements A, B, C, D, E, F and G have a different number of electronic shells but have the same number of electrons in their outermost shells. The elements A and C combine with chlorine to form an acid and common salt respectively. The oxide of element A is liquid at room temperature and is a neutral substance, while the oxides of the remaining six elements are basic in nature. Based on the above information, answer the following questions: What could the element A be?
(i) Will elements A to G belong to the same period or same group of the periodic table?
(iii) Write the formula of the compound formed by the reaction of the element A with oxygen,
(iv) Show the formation of the compound by a combination of element C with chlorine with the help of electronic structure.
(v) What would be the ratio of number of combining atoms in a compound formed by the combination of element A with carbon?
(vi)Which one of the given elements is likely to have the smallest atomic radius?
Answer: (i)’A’ is hydrogen because its oxide H2O is liquid at room temperature .
(ii) A to G belong to same group of the periodic table as these have same number of valence electrons. img

Question. How many groups and periods are there in the Modern Periodic Table? How do the atomic size and metallic character of elements vary as we move
a. down a group and b. from left to right in a period?
Answer: There are 7 periods in Modern Periodic Table.
Valency first increases and then decreases. Metallic character decreases along a period from left to right.
There is no change in valency down the group.
Atomic size increases down the group.

Question. a. Define the following terms (i) Valency, (ii) Atomic size
b. How do the valency and the atomic size of the elements vary while going from left to right along a period in the modern periodic table?
Answer: a. (i) Valency: It is the number of electrons lost or gained or shared by an atom.
(ii) Atomic size: It is the distance between centre of the nucleus and outermost shell of an atom.
b. Valency first increases till middle and then decreases. Atomic size decreases from left to right along a period.