Periodic Classification of Elements
Q1. Rearrange the columns 2 and 3 so as to match with the column 1.
| I | II | III |
|---|---|---|
| Triad | Lightest and negatively charged particle in all the atoms | Mendeleev |
| Octave | Concentrated mass and positive charge | Thomson |
| Atomic number | Average of the first and the third atomic mass | Newlands |
| Period | Properties of the eighth element similar to the first | Rutherford |
| Nucleus | Positive charge on the nucleus | Dobereiner |
| Electron | Sequential change in molecular formulae | Moseley |
Solution:-
| I | II | III |
|---|---|---|
| Triad | Average of the first and the third atomic mass | Dobereiner |
| Octave | Properties of the eighth element similar to the first | Newlands |
| Atomic number | Positive charge on the nucleus | Mendeleev |
| Period | Sequential change in molecular formulae | Moseley |
| Nucleus | Concentrated mass and positive charge | Rutherford |
| Electron | Lightest and negatively charged particle in all the atoms | Thomson |
Q2.Choose the correct option and rewrite the statement.
1.The number of electrons in the outermost shell of alkali metals is......
(i) 1 (ii) 2 (iii) 3 (iv) 7
The correct answer is (i) 1
2. Alkaline earth metals have valency 2. This means that their position in the modern periodic table is in .....
(i) Group 2 (ii) Group16 (iii) Period 2 (iv) d-block
The correct answer is (i) Group 2
3. Molecular formula of the chloride of an element X is XCl. This compound is a solid having high melting point. Which of the following elements be present in the same group as X.
(i) Na (ii) Mg (iii) Al (iv) Si
The correct answer is (i) Na
4. In which block of the modern periodic table are the nonmetals found?
(i) s-block (ii) p-block (iii) d-block (iv) f-block
The correct answer is (ii) p-block
Q3. An element has its electron configuration as 2,8,2. Now answer the following questions.
a. What is the atomic number of this element?
Ans:-The atomic number of this element is 12.
b. What is the group of this element?
Ans:-The group of this element is Group 2 (alkaline earth metals).
c. To which period does this element belong?
Ans:-This element belongs to Period 3.
d. With which of the following elements would this element resemble? (Atomic numbers are given in the brackets)
N (7), Be (4) , Ar (18), Cl (17)
Ans:-This element would resemble Be (4) in terms of valence electron configuration.
Q4. Write down the electronic configuration of the following elements from the given atomic numbers. Answer the following question with explanation.
1. 3Li, 14Si, 2He, 11Na, 15P Which of these elements belong to be period 3?
Ans:-The electronic configurations of the given elements are as follows:
a. Li (atomic number 3): 1s² 2s¹
b. Si (atomic number 14): 1s² 2s² 2p⁶ 3s² 3p²
c. He (atomic number 2): 1s²
d. Na (atomic number 11): 1s² 2s² 2p⁶ 3s¹
e. P (atomic number 15): 1s² 2s² 2p⁶ 3s² 3p³
Na, Si, and P are elements belonging to period 3.
2. 1H, 7N, 20Ca, 16S, 4Be, 18Ar Which of these elements belong to the second group?
H (atomic number 1): 1s¹
N (atomic number 7): 1s² 2s² 2p³
Ca (atomic number 20): 1s² 2s² 2p⁶ 3s² 3p⁶ 4s²
S (atomic number 16): 1s² 2s² 2p⁶ 3s² 3p⁴
Be (atomic number 4): 1s² 2s²
Ar (atomic number 18): 1s² 2s² 2p⁶ 3s² 3p⁶
Ca and Be belong to the second group (Group 2).
3. 7N, 6C, 8O, 5B, 13Al Which is the most electronegative element among these?
7N (nitrogen): 1s² 2s² 2p³
6C (carbon): 1s² 2s² 2p²
8O (oxygen): 1s² 2s² 2p⁴
5B (boron): 1s² 2s² 2p¹
13Al (aluminum): 1s² 2s² 2p⁶ 3s² 3p¹
oxygen (O) is the most electronegative element.
4. 4Be, 6C, 8O, 5B, 13A1 Which is the most electropositive element among these?
4Be (beryllium): 1s² 2s²
6C (carbon): 1s² 2s² 2p²
8O (oxygen): 1s² 2s² 2p⁴
5B (boron): 1s² 2s² 2p¹
13Al (aluminum): 1s² 2s² 2p⁶ 3s² 3p¹
Al is the most electropositive element
5. 11Na, 15P, 17C1, 14Si, 12Mg Which of these has largest atoms?
11Na (Sodium): 1s² 2s² 2p⁶ 3s¹
15P (Phosphorus): 1s² 2s² 2p⁶ 3s² 3p³
17Cl (Chlorine): 1s² 2s² 2p⁶ 3s² 3p⁵
14Si (Silicon): 1s² 2s² 2p⁶ 3s² 3p²
12Mg (Magnesium): 1s² 2s² 2p⁶ 3s²
Based on the electronic configurations, the element with the largest atomic size is 11Na (Sodium).
6. 19K, 3Li, 11Na, 4Be Which of these atoms has smallest atomic radius?
19K: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹
3Li: 1s² 2s¹
11Na: 1s² 2s² 2p⁶ 3s¹
4Be: 1s² 2s²
4Be has smallest atomic radius
7. 13A1, 14Si, 11Na, 12Mg, 16S Which of the above elements has the highest metallic character?
13Al (aluminum): [Ne] 3s² 3p¹
14Si (silicon): [Ne] 3s² 3p²
11Na (sodium): [Ne] 3s¹
12Mg (magnesium): [Ne] 3s²
16S (sulfur): [Ne] 3s² 3p⁴
sodium has the highest metallic character among the listed elements.
8. 6C, 3Li, 9F, 7N, 8O Which of the above elements has the highest nonmetallic character?
6C (carbon): 1s² 2s² 2p²
3Li (lithium): 1s² 2s¹
9F (fluorine): 1s² 2s² 2p⁵
7N (nitrogen): 1s² 2s² 2p³
8O (oxygen): 1s² 2s² 2p⁴
fluorine has the highest nonmetallic character among the listed elements.
Q5. Write the name and symbol of the element from the description.
A. The atom having the smallest size.
Ans:-The atom with the smallest size is hydrogen (H).
B. The atom having the smallest atomic mass.
Ans:- The element with the smallest atomic mass is hydrogen (H).
C. The most electronegative atom.
Ans:-The most electronegative atom is fluorine (F).
D. The noble gas with the smallest atomic radius.
Ans:- The noble gas with the smallest atomic radius is helium (He).
E. The most reactive nonmetal.
Ans:- The most reactive nonmetal is fluorine (F).
Q6. Write short notes.
A. Mendeleev’s periodic law.
Ans:- According to Mendeleev's periodic law, the characteristics of elements repeat periodically based on their atomic masses. He discovered that elements with similar properties tended to occur at regular intervals by arranging the elements in order of increasing atomic mass. As a result, the periodic table was created, which divides elements into groups and periods based on the traits they have in common. As we move across periods and down groups, the periodic table makes it simple to recognise and comprehend trends in properties like atomic radius, electronegativity, and chemical reactivity.
B. Structure of the modern periodic table.
Ans :- The modern periodic table is a systematic arrangement of elements based on their atomic number, electron configuration, and recurring chemical properties. It is divided into periods (horizontal rows) and groups (vertical columns) that help organize and classify the elements.
There are seven periods in the periodic table, numbered from 1 to 7. Each period represents a different energy level or shell in which the electrons of the elements are arranged. There are 18 groups in the periodic table, labeled from 1 to 18. Elements within the same group share similar chemical properties due to the same number of valence electrons. The periodic table is divided into blocks based on the type of subshell being filled by electrons. These blocks are s-block, p-block, d-block, and f-block.
The d-block elements, located in groups 3-12, are called transition elements. They possess characteristic properties, such as variable oxidation states and the formation of colorful compounds.
C. Position of isotopes in the Mendeleev’s and the modern periodic table.
Ans:- In Mendeleev's periodic table, there were no specific places designated for isotopes. The table was primarily organized based on the elements' atomic masses and chemical properties. Isotopes, being variants of an element with different atomic masses, were not given separate positions in the periodic table. This was due to the fact that Mendeleev's focus was on arranging elements based on their chemical properties and similarities rather than explicitly accounting for isotopic variations.
Q7. Write scientific reasons.
A. Atomic radius goes on decreasing while going from left to right in a period.
Ans:- As the atomic number of the elements rises, the number of protons and electrons in the atoms rises as well (the extra electrons being added to the same shell), and this causes the atomic radius to continue decreasing while moving from left to right in a period. The electrons are drawn inward towards the nucleus as a result of a strong positive charge on the nucleus, which reduces the size of an atom.
B. Metallic character goes on decreasing while going from left to right in a period.
Ans:- The increasing nuclear charge, which is the result of the increasing number of protons in the nucleus, leads to a stronger attraction between the nucleus and the valence electrons. This increased attraction makes it more difficult for the atoms to lose electrons and exhibit metallic behavior. As a result, elements on the left side of a period (which have fewer protons and a weaker nuclear charge) are more likely to lose electrons and display metallic properties, while elements on the right side (with higher nuclear charge) have a stronger hold on their valence electrons and exhibit more nonmetallic behavior. This trend contributes to the overall decrease in metallic character while moving from left to right in a period.
C. Atomic radius goes on increasing down a group.
Ans:- As we move from top to bottom in a group of the periodic table, a new shell of electrons is added to the atoms at each step. The addition of a new energy level increases the distance between the nucleus and the outermost electrons. This results in an increase in the atomic radius of the atoms in the group.
D. Elements belonging to the same group have the same valency.
Ans:- Elements belonging to the same group have the same valency because they have the same number of valence electrons. Valence electrons determine an element's ability to form chemical bonds, and elements in the same group have similar electronic configurations with the same number of valence electrons. This similarity in valence electron count leads to similar chemical behavior and the same valency among elements in the group.
E. The third period contains only eight elements even through the electron capacity of the third shell is 18 .
Ans:- The third period contains only eight elements despite the electron capacity of the third shell being 18 because the third period follows the rule of filling the 2s and 2p orbitals. The 2s orbital can accommodate a maximum of 2 electrons, and the 2p orbitals can accommodate a maximum of 6 electrons. Therefore, in the third period, after filling the 2s and 2p orbitals with 8 electrons, the remaining orbitals are not energetically favorable for filling in that period. As a result, the third period consists of only eight elements.
Q8. Write the names from the description.
A. The period with electrons in the shells K, L and M.
Ans:- The period with electrons in the shells K, L, and M is the third period of the periodic table.
B. The group with valency zero.
Ans:-The group with valency zero is indeed known as the noble group or noble gases.
C. The family of nonmetals having valency one.
Ans:-The family of nonmetals having valency one is known as the halogens.
D. The family of metals having valency one.
Ans:-The family of metals having valency one is known as the alkali metals.
E. The family of metals having valency two.
Ans:- The family of metals having valency two is known as the alkaline earth metals.
F. The metalloids in the second and third periods.
Ans:-The metalloids in the second period are Boron (B) and in the third period is Silicon (Si).
G. Nonmetals in the third period.
Ans:-The nonmetals in the third period include sulfur (S) and chlorine (Cl).
H. Two elements having valency 4.
Ans:-The two elements having valency 4 are carbon (C) and silicon (Si).
Find out the applications of all the inert gases, prepare a chart and display it in the class.
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| Inert Gas | Applications |
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| Helium | - Filling balloons and airships |
| | - Cooling agent in cryogenics |
| | - Gas chromatography |
| | - Welding and leak detection |
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| Neon | - Neon signs and lighting |
| | - Advertising displays |
| | - High-voltage indicators |
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| Argon | - Shielding gas in welding |
| | - Lighting (incandescent and fluorescent)|
| | - Blanket gas in metallurgical processes|
| | - Insulation in double-pane windows |
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| Krypton | - Lighting (halogen bulbs, flashlights)|
| | - Laser technology |
| | - High-speed photography |
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| Xenon | - Lighting (high-intensity discharge lamps)|
| | - Strobe lights and flash photography |
| | - Medical imaging (Xenon CT) |
| | - Ion propulsion systems (spacecraft) |
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| Radon | - Radiotherapy for cancer treatment |
| | - Geological surveys for gas and oil |
| | - Research in materials science |
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