Punjab State Board PSEB 10th Class Science Book Solutions Chapter 5 Periodic Classification of Elements Textbook Exercise Questions and Answers.
PSEB Solutions for Class 10 Science Chapter 5 Periodic Classification of Elements
PSEB 10th Class Science Guide Periodic Classification of Elements Textbook Questions and Answers
Question 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.
(а) 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:
(c) The atoms lose their electrons more easily.
Question 2.
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
Answer:
(b) Mg
Question 3.
Which element has :
(а) two shells, both of which are completely filled with electrons?
Answer:
Neon
(b) the electronic configuration 2, 8, 2?
Answer:
Magnesium
(c) a total of three shells, with four electrons in its valence shell?
Answer:
Silicon
(d) a total of two shells, with three electrons in its valence shell?
Answer:
Boron
(e) twice as many electrons in its second shell as in its first shell?
Answer:
Carbon.
Question 4.
(a) What property do all elements in the same column of the periodic table as Boron have in common?
Answer:
All elements of this column have 3 electrons in their valence shell like Boron.
(b) What property do all elements in the same column of the periodic table as Fluorine have in common?
Answer:
All elements of this column have 7 electrons in their valence shell like fluorine.
Question 5.
An atom has electronic configuration 2, 8, 7.
(а) What is the atomic number of this element?
Answer:
17
(b) To which of the following element would it be chemically similar? (atomic numbers are given in parenthesis).
N (7), F (9), P (15), Ar (18).
Answer:
F (9) (2, 7)
Question 6.
The position of three elements A, B and C in the periodic table are as shown below :
(а) State whether A is a metal or non-metal.
Answer:
A is non-metal.
(b) State whether C is more reactive or less reactive than A.
Answer:
C is less reactive than A.
(c) Will C be larger or smaller in size than B.
Answer:
C has smaller size than B.
(d) Which type of ion, cation or anion, will be formed by element A?
Answer:
Anion, A-.
Question 7.
Nitrogen (atomic number 7) and phosphorus (atomic number 15) belong to group 15 of the periodic table. Write the electronic configurations of these two elements. Which of these will be more electronegative? Why?
Answer:
| K | L | M | |
| N7 has electronic configuration | 2 | 5 | |
| P15 has electronic configuration | 2 | 8 | 7 |
Nitrogen is more electronegative than Phosphorus due to smaller size.
Question 8.
How does the electronic configuration of an atom relate to its position in the Modern Periodic Table?
Answer:
By knowing the electronic configuration of an element, we can know its period number from the number of shells present in its atom and from number of electrons in the valence shell of its atoms we can know its group number, e.g. let us consider the case of sodium atom.
Atomic number of sodium = 11
Its electronic configuration = 2, 8, 1 (K) (L) (M)
∴ Number of shells = 3
∴ Sodium belongs to 3rd period.
Also sodium atom has one electron in its valence shell.
∴ It is present in first group.
∴ Sodium lies in the first group and third period of Modern Periodic Table.
Question 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 numbers 12 and 38 because they have two electrons in their valence shells like calcium (2, 8, 8, 2).
Question 10.
Compare and contrast the arrangement of elements in Mendeleev’s Periodic table and the Modern Periodic table.
Answer:
Similarities :
- In both the elements are arranged in groups and periods.
- In both similar elements are placed in same group.
- Both the classification make the study of elements simple and systematic.
Differences :
| Mendeleev’s Periodic Table | Modern Periodic Table |
| 1. The elements are arranged in order of increasing mass numbers. | 1. The elements are arranged in order of increasing atomic numbers. |
| 2. It has 8 vertical columns called groups. | 2. It contains eighteen vertical columns called groups. |
| 3. Groups like group VIII ‘have been divided into sub groups A and B. | 3. Each group is an independent group. |
| 4. Inert gases are not included in this table. | 4. Inert gases are included in this periodic table. |
Science Guide for Class 10 PSEB Periodic Classification of Elements InText Questions and Answers
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 columns of Newlands’ octaves. These are:
| H | Li | Be |
| F | Na | Mg |
| Cl | K | Ca |
Question 2.
What were the limitations of Dobereiner’s classification?
Answer:
- Dobereiner could find only three triads from the elements known at that time.
- It is applicable only to a few elements.
Question 3.
What were the limitations of Newlands’ law of octaves?
Answer:
- It is applicable upto calcium only.
- Sometimes two elements were put in the same slot.
- After the discovery of noble gas, law of octave is not valid.
Question 4.
Use Mendeleev’s periodic table to predict the formulae for the oxides of following elements :
K, C, Al, Si, Ba.
Answer:
K2O, CO2, Al2O3, SiO2, BaO.
Question 5.
Besides Gallium, which other elements have since been discovered to fill the gaps left by Mendeleev in his periodic table? (any two)
Answer:
Scandium and Germanium.
Question 6.
What were the criteria used by Mendeleev in creating his periodic table?
Answer:
- The formulae of hydrides and oxides formed by an element wrere treated as one of the basic properties of an element for its classification.
- It is based upon Mendeleev’s periodic law which predicts that the properties of the elements are the periodic function of their atomic masses.
Question 7.
Why do you think the noble gases are placed in a separate group?
Answer:
These gases were discovered very late because they are very inert and placing them in a separate group, does not disturb the existing order put forward by Mendeleev.
Question 8.
How could Modern Periodic Table remove various anomalies of Mendeleev Periodic Table?
Answer:
- Isotopes of an elements occupy same position in the periodic table due to same atomic number.
- There is a logical separation of elements into subgroups.
- It is based upon the fundamental property of an element i.e. atomic number.
Question 9.
Name two elements you would expect to show same kind of chemical reactivity as magnesium. What is the basis for your choice?
Answer:
Calcium and Strontium because they have same number of valence electrons.
Question 10.
Name :
(а) three elements that have only a single electron in their outermost shells.
Answer:
Lithium, Sodium and Potassium.
(b) two elements that have two electrons in their outermost shells.
Answer:
Magnesium, Calcium.
(c) three elements with filled outermost shells.
Answer:
Neon, Argon, Krypton.
Question 11.
(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:
One electron in their valence shells and are metals.
(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:
Eight electrons in their valence shells.
Question 12.
In the modern periodic table, of the first ten elements, which are metals?
Answer:
Lithium and Beryllium.
Question 13.
By considering their position in the periodic table, which one of the following elements would you expect to have the most metallic characteristics?
Ga Ge As Se Be.
Answer:
Gallium.