Chapter 2:- Periodic Classification of Element
Chapter 3:- Chemical Reaction and Equation
Chapter 4:- Effect of Electric Current
Chapter 5 :- Heat
Chapter 6 Refraction of Light
Chapter 7:- Lenses
Chapter 8 :- Metallurgy
Chapter 9 Carbon Compound
Chapter 10 :- Space Mission
Textbook Exercise
1. Rearrange the columns 2 and 3 so as to match with the column 1.
| Column 1 | Column 2 | Column 3 |
|---|---|---|
| i. Triad ii. Octave iii. Atomic number iv. Period v. Nucleus vi. Electron |
a. Lightest and negatively charged particle in all the atoms b. Concentrated mass and positive charge c. Average of the first and the third atomic mass d. Properties of the eighth element similar to the first e. Positive charge on the nucleus f. Sequential change in molecular formulae |
1.Mendeleev
2. Thomson
3. Newlands
4. Rutherford
5. Dobereiner
. Moseley
|
Answer:-
| Column I | Column II | Column III |
|---|---|---|
| i. Triad | c. Average of the first and the third atomic mass | 5. Dobereiner |
| ii. Octave | d. Properties of the eight-element similar to the first. | 3. Newlands |
| iii. Atomic Number | e. Positive charge on the nucleus. | 6. Moseley |
| iv. Period | f. Sequential change in molecular formulae | 1. Mendeleev |
| v. Nucleus | b. Concentrated mass and positive charge | 4. Rutherford |
| vi. Electron | a. Lightest and negatively charged particle in all the atoms | 2. Thomson |
2. Choose the correct option and rewrite the statement.
a. The number of electrons in the outermost shell of alkali metals is……
(i) 1 (ii) 2 (iii) 3 (iv) 7.
Answer:- 1
b. 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
Answer:- Group 2
c. 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
Answer:- Na
d. In which block of the modern periodic table are the nonmetals found?
(i) s-block (ii) p-block (iii) d-block (iv) f-block
Answer:- P block
3. An element has its electron configuration as 2,8,2. Now answer the following questions.
a. What is the atomic number of this element?
Answer:- The atomic number of element is 12
b. What is the group of this element?
Answer:- The group of this element is 2
c. To which period does this element belong?
Answer:- Element belong to third period
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)
Answer:- The element would resemble Beryllium
4. Write down the electronic configuration of the following elements from the given atomic numbers. Answer the following question with explanation.
a. 3Li, 14Si, 2He, 11Na, 15P Which of these elements belong to be period 3?
Answer:-
3Li, 14Si, 2He, 11Na, 15P
Electronic configuration of the following elements is:
3Li = 2,1
14Si = 2,8,4
2He = 2
11Na = 2,8,1
15P = 2,8,5
14Si, 11Na, 15P belong to the third period because according to their electronic configuration, each element contains three shells i.e. K,L,M.
b. 1H, 7N, 20Ca, 16S, 4Be, 18Ar Which of these elements
belong to the second group?
Answer:-
1H, 7N, 20Ca, 16S, 4Be, 18Ar
Electronic configuration of the following elements is:
1H = 1
7N = 2,5
20Ca = 2,8,8,2
16S = 2,8,6
4Be = 2,2
18Ar = 2,8,8
20Ca, 4Be belong to second group because these elements have 2 electrons in its outermost shell.
c. 7N, 6C, 8O, 5B, 13A1 Which is the most electronegative element among these?
Answer:-
7N, 6C, 8O, 5B, 13Al
Electronic configuration of the following elements is:
7N =2,5
6C = 2,4
8O = 2,6
5B = 2,3
13Al = 2,8,3
8O is the most electronegative element among these because electronegativity increases as we move from left to right in a period of the periodic table.
d. 4Be, 6C, 8O, 5B, 13A1 Which is the most electropositive element among these?
Answer:-
4Be, 6C, 8O, 5B, 13Al
Electronic configuration of the following elements is:
4Be = 2,2
6C = 2,4
8O = 2,6
5B = 2,3
13Al = 2,8,3
13Al is the most electropositive element among these because 4Be, 6C, 8O, 5B belong to same period, but 13Al belong to next period. According to the trend, electropositive character of an elements increases as we move from top to bottom in a group of the periodic table. This happens as the tendency of an atom to lose electrons increases due to decrease in nuclear charge and increase in numbers of shell.
e. 11Na, 15P, 17C1, 14Si, 12Mg Which of these has largest atoms?
Answer:-
11Na, 15P, 17Cl, 14Si, 12Mg
Electronic configuration of the following elements is:
11Na = 2,8,1
15P = 2,8,5
17Cl = 2,8,7
14Si = 2,8,4
12Mg = 2,8,2
11Na has largest size among these because according to the trend, atomic radius decreases as we move from left to right in a period of the periodic table. The atomic number of elements increases which means the number of protons and electrons in the atoms increases. Due to large positive charge on the nucleus, the electrons are pulled closer to the nucleus and the size of atom decreases.
f. 19K, 3Li, 11Na, 4Be Which of these atoms has smallest atomic radius?
Answer:-
19K, 3Li, 11Na, 4Be
Electronic configuration of the following elements is:
19K = 2,8,8,1
3Li = 2,1
11Na = 2,8,1
4Be = 2,2
4Be has smallest atomic radius because 19K, 3Li, 11Na are present in same group 1 but Be is present in group 2. According to the trend, as we move from left to right atomic size of an atoms decreases. Due to large positive charge on the nucleus, the electrons are pulled closer to the nucleus and the size of atom decreases.
g. 13A1, 14Si, 11Na, 12Mg, 16S Which of the above elements has the highest metallic character?
Answer:_
13Al, 14Si, 11Na, 12Mg, 16S
Electronic configuration of the following elements is:
3Al = 2,8,3
14Si = 2,8,4
11Na = 2,8,1
12Mg = 2,8,2
16S = 2,8,6
11Na has the highest metallic character because metallic character of an elements decreases as we move from left to right in a modern periodic table. This happens as the tendency of an atom to lose electrons decreases due to gradual increase in the number of protons and nuclear charge.
h. 6C, 3Li, 9F, 7N, 😯 Which of the above elements has the highest nonmetallic character?
Answer:-
6C, 3Li, 9F, 7N, 8O
Electronic configuration of the following elements is:
6C = 2,4
3Li = 2,1
9F = 2,7
7N = 2,5
8O = 2,6
9F has the highest nonmetallic character because non-metallic character of an elements increases as we move from left to right in a period of the periodic table. This happens as the tendency of an atom to gain electrons increases due to increase in nuclear charge, the valence electrons are pulled in strongly by the nucleus and it becomes easier for an atom to gain electrons.
5. Write the name and symbol of the element from the description.
a. The atom having the smallest size.
Answer:-
The atom having the smallest size = Helium (He)
b. The atom having the smallest atomic mass.
Answer:-
The atom having the smallest atomic mass = Hydrogen (H)
c. The most electronegative atom.
Answer:-
The most electronegative atom is Fluorine (F) its electronegativity is 4
d. The noble gas with the smallest atomic radius.
Answer:- The noble gas with the smallest atomic radius in Helium
e. The most reactive nonmetal.
Answer:_
The most reactive nonmetal is Fluorine (F)
6. Write short notes.
a. Mendeleev’s periodic law.
Answer:_
Mendeleev’s periodic table was a significant contribution to the field of chemistry, as it provided a systematic way of organizing and understanding the elements. Some of the key features of Mendeleev’s periodic table are:
It was based on Mendeleev’s Periodic Law, which stated that the physical and chemical properties of elements are a periodic function of their atomic masses.
Elements were classified according to their atomic masses and arranged in increasing order of their atomic masses.
The periodic table was divided into horizontal rows called periods and vertical columns called groups. Elements with similar properties were placed in the same group.
Mendeleev left gaps in the periodic table for undiscovered elements and predicted their properties.
Despite its many strengths, Mendeleev’s periodic table had some limitations, including:
The position of isotopes could not be explained, as they have the same atomic number but different atomic masses.
The wrong order of atomic masses of some elements could not be explained.
The position of Hydrogen could not be assigned in a periodic table, as it has properties that are both similar and dissimilar to those of other elements.
Despite these limitations, Mendeleev’s periodic table was a groundbreaking achievement in the field of chemistry and laid the foundation for the development of modern periodic tables.
b. Structure of the modern periodic table.
Answer:-
The modern periodic table is based on the modern periodic law, which states that the chemical and physical properties of elements are a periodic function of their atomic numbers. Some of the key features of the modern periodic table are:
The vertical columns in the periodic table are called groups, and there are 18 groups in total. Elements in the same group have similar chemical and physical properties due to their similar electron configurations.
The horizontal rows in the periodic table are called periods, and there are 7 periods in total. Elements in the same period have the same number of electron shells.
The periodic table is divided into four main blocks: s-block, p-block, d-block, and f-block. The elements in the s-block and p-block are called main group elements, while the elements in the d-block and f-block are called transition and inner transition elements, respectively.
The s-block contains the alkali metals (group 1) and alkaline earth metals (group 2), which are highly reactive due to their low ionization energies.
The p-block contains the nonmetals, metalloids, and some metals. Group 18 contains the noble gases, which are chemically inert due to their full valence electron shells.
The d-block contains the transition elements, which have partially filled d orbitals and exhibit a wide range of oxidation states.
The f-block contains the inner transition elements, which have partially filled f orbitals and exhibit similar chemical properties due to their similar electron configurations.
Overall, the modern periodic table provides a systematic and organized way to understand the properties and behavior of the elements.
c. Position of isotopes in the Mendeleev’s and the modern periodic table.
Answer:-
Isotopes have different atomic masses but the same atomic number, indicating that they have the same number of protons but different numbers of neutrons. In Mendeleev’s periodic table, isotopes were not given separate positions based on their atomic masses because they have similar chemical properties. This was a drawback of Mendeleev’s periodic table as he could not explain the position of isotopes.
In the modern periodic table, elements are arranged in increasing order of their atomic number, so isotopes of an element are placed in the same position in the periodic table. The position of isotopes is determined by their atomic number rather than their atomic mass. This means that all isotopes of hydrogen are placed in the same position based on their atomic number, rather than being placed at different positions based on their atomic masses.
7. Write scientific reasons.
a. Atomic radius goes on decreasing while going from left to right in a period.
Answer:-
The atomic radius is defined as half the distance between the nuclei of two identical atoms that are bonded together. The scientific reason for the decrease in atomic radius as we move from left to right across a period in the periodic table is due to the increase in the effective nuclear charge.
The effective nuclear charge is the net positive charge experienced by an electron in an atom. It is calculated by subtracting the number of core electrons (inner-shell electrons) from the total number of protons in the nucleus. As we move from left to right in a period, the number of protons in the nucleus increases while the number of core electrons remains the same. This causes an increase in the effective nuclear charge.
As the effective nuclear charge increases, the attractive force between the nucleus and the electrons in the outermost shell increases. This pulls the outermost electrons closer to the nucleus, making the atomic radius smaller. Thus, the atomic radius decreases as we move from left to right in a period.
b. Metallic character goes on decreasing while going from left to right in a period.
Answer:-
The metallic character of an element is related to its ability to lose electrons easily and form cations. The tendency to lose electrons depends on the effective nuclear charge (Zeff) experienced by the valence electrons and the distance between the valence electrons and the nucleus.
As we move from left to right in a period, the number of valence electrons remains the same, but the effective nuclear charge increases due to the increasing atomic number. This is because the number of protons in the nucleus increases, which attracts the valence electrons more strongly towards the nucleus, thereby increasing the Zeff. This makes it harder for the valence electrons to be removed from the atom, which decreases the metallic character of the elements.
Additionally, as we move from left to right in a period, the size of the atoms decreases due to the increasing Zeff. This decreases the distance between the valence electrons and the nucleus, which makes it harder for the valence electrons to be removed. This also contributes to the decreasing metallic character of the elements.
Therefore, due to the combined effect of increasing Zeff and decreasing atomic size, the metallic character of elements goes on decreasing while going from left to right in a period.
c. Atomic radius goes on increasing down a group.
Answer:-
The atomic radius of an atom is defined as the distance between the nucleus of the atom and its outermost electrons. When we move down a group, the number of occupied electron shells increases. This happens because as we move down a group, the number of energy levels (or shells) occupied by electrons increases.
Since the distance between the outermost electrons and the nucleus increases as more energy levels are added, the atomic radius increases as we move down a group. This increase in atomic radius down a group is due to the fact that the electrons occupy energy levels that are further away from the nucleus, which causes the size of the atom to increase.
d. Elements belonging to the same group have the same valency.
Answer:-
Elements belonging to the same group in the periodic table have the same valency or valence electron configuration. This is because elements in the same group have the same number of valence electrons in their outermost shell, which determines the chemical behavior of the elements. For example, all elements in group 1 (alkali metals) have one valence electron, and all elements in group 17 (halogens) have seven valence electrons. This similarity in the number of valence electrons results in similar chemical behavior, including similar reactivity and similar tendency to form ions with the same charge. Therefore, the valency of elements in the same group is the same.
e. The third period contains only eight elements even through the electron capacity of the third shell is 18 .
Answer:-
The third period of the periodic table contains only eight elements (sodium, magnesium, aluminum, silicon, phosphorus, sulfur, chlorine, and argon) even though the electron capacity of the third shell is 18. This is because the third shell is not completely filled by any of the elements in the third period. The first two elements (sodium and magnesium) have their valence electrons in the second shell, while the next six elements (aluminum through chlorine) have their valence electrons in the third shell. Argon, the last element in the third period, has a completely filled third shell with eight valence electrons. Therefore, the third period contains only elements with valence electrons in the second and third shells, and the remaining ten elements with valence electrons in the fourth and higher shells are found in the fourth and subsequent periods of the periodic table.
8. Write the names from the description.
a. The period with electrons in the shells K, L and M.
Answer:-
Third Period
b. The group with valency zero.
Answer:-
18 group element ( Noble Group)
c. The family of nonmetals having valency one.
Answer:-
Halogen Family
d. The family of metals having valency one.
Answer:-
Alkali Metal
e. The family of metals having valency two.
Answer:-
Alkaline Earth Metal
f. The metalloids in the second and third periods.
Answer:_
Boron( Second Period), Silicon ( Third Period)
g. Nonmetals in the third period.
Answer:-
Phosphorus, Sulphur, Chlorine and Argon
h. Two elements having valency 4.
Answer:-
Carbon and Silicon