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Practice each question, then open the answer or worked solution.
What is the basic theme of organisation in the periodic table?
Ans :
The primary idea of the periodic table's organisation is to organise elements into periods and groups based on their qualities. This arrangement simplifies and organises the study of elements and their compounds. Elements with comparable characteristics are grouped together in the periodic table.
Which important property did Mendeleev use to classify the elements in his periodic table and did he stick to that?
Ans :
In his periodic chart, Mendeleev organised the elements by atomic weight or mass. In order of increasing atomic weight, he divided the elements into periods and groups. He grouped elements that have comparable qualities together. He did not, however, keep this arrangement for long. He discovered that if the elements were ordered strictly in order of increasing atomic weights, several of them would not fit into this classification scheme.
As a result, in certain circumstances, he neglected the atomic weight order. The atomic weight of iodine, for example, is smaller than that of tellurium. Despite this, Mendeleev ranked tellurium (Group VI) ahead of iodine (Group VII) because the characteristics of iodine are so similar to fluorine, chlorine, and bromine.
What is the basic difference in approach between Mendeleev's Periodic Law and the Modern Periodic Law?
Ans:
Mendeleev's Periodic Law | Modern Periodic Law |
Based on atomic mass and chemical properties. | Based on atomic number and chemical properties. |
Arranged elements in increasing order of atomic mass. | Arranged elements in increasing order of atomic number. |
Left gaps for undiscovered elements and predicted their properties. | No provision for gaps; elements placed strictly according to atomic number. |
Isotopes are placed in the same slot based on average atomic mass. | Each isotope is considered as a separate entity and placed accordingly. |
Elements with similar chemical properties placed in the same group. | Similar chemical behaviour attributed to elements in the same group. |
Initially faced scepticism but gained acceptance over time. | Widely accepted and forms the basis of the modern periodic table. |
On the basis of quantum numbers, justify that the sixth period of the Periodic Table should have 32 elements.
Ans :
A period is the value of the primary quantum number $\left( n \right)$ for the outermost shells in the periodic table of the elements. The filling of the primary quantum number begins each period $\left( n \right).$ For the sixth period, the value of $\left( n \right)$ is 6. The azimuthal quantum number $\left( l \right)$ for $n = 6$ can be $0,1,2,{\text{3 or }}4.$ The Aufbau principle states that electrons are introduced to distinct orbitals in order of increasing energy. The $6d$ subshell has an even higher energy than the $7s$ subshell.
Only the $6s,4f,5d{\text{ and 6}}p$ subshells can be filled by electrons in the ${6^{th}}$ period. Now, the $6s$ has one orbital, the $4f$ has seven, the $5d$ has five, and the $6p$ has three. As a result, there are a total of sixteen orbitals available $\left( {1 + 7 + 5 + 3 = 16} \right).$ Each orbital can only hold two electrons, according to Pauli's exclusion principle. As a result, 16 orbitals can hold a maximum of 32 electrons. As a result, the periodic table's sixth period should have 32 elements.
In terms of period and group, where would you locate the element with \[Z = 114?\]
Ans :
The periodic table's ${7^{th}}$ period has elements with atomic values ranging from $Z = 87 - 114.$ As a result, the element with $Z = 114$ is found in the periodic table's ${7^{th}}$ period. The first two elements with $Z = 87$ and $Z = 88$ are $s$-block elements in the seventh period, while the next 14 elements with $Z = 90 - 103$ are $f$-block elements. $d$ – block elements are those with $Z = 89$ and $Z = 104 - 112,$ whereas $p$ – block elements are those with $Z = 113 - 118.$ As a result, in the ${7^{th}}$ period, the element with $Z = 114$ is the second $p$ – block element. As a result, the element with $Z = 114$ is found in the periodic table's ${7^{th}}$ period and ${4^{th}}$ group.
Write the atomic number of the element present in the third period and the seventeenth group of the Periodic Table.
Ans:
The first phase has two elements, while the second period has eight. The element with \[Z = 11,\] begins the third period. In the third period, there are now eight elements. As a result, the third period finishes with the element with \[Z = 18,\] i.e., the element in the third period's ${18^{th}}$ group. As a result, the element in the third period's ${17^{th}}$ group has the atomic number \[Z = 17.\]
Which element do you think would have been named by (i) Lawrence Berkeley Laboratory (ii) Seaborg’s Group?
Ans :
(i) Lawrencium $\left( {{\text{Lr}}} \right)$ has a $Z$ of 103 while, Berkelium $\left( {{\text{Bk}}} \right)$ has a $Z$ of 97.
(ii) Seaborgium $\left( {{\text{Sg}}} \right)$ has a $Z$ of 106.
Why do elements in the same group have similar physical and chemical properties?
Ans :
The quantity of valence electrons affects the physical and chemical properties of elements. The number of valence electrons in a group of elements is the same. As a result, physical and chemical properties of elements in the same group are comparable.
What does atomic radius and ionic radius really mean to you?
Ans :
The radius of an atom is known as its atomic radius. It is used to determine the size of an atom. If the element is a metal, the atomic radius is the metallic radius; if it is a nonmetal, the atomic radius is the covalent radius. The internuclear distance separating the metal cores in a metallic crystal is half the metallic radius. In solid copper, for example, the internuclear distance between two neighbouring copper atoms is ${\text{256 pm}}{\text{.}}$ As a result, the metallic radius of copper is calculated to be,
\[{\text{Metallic radius of copper}} = \dfrac{{256}}{2}\\ = {\text{128 pm}}\]
In a covalent molecule, the covalent radius is the distance between two atoms when they are connected by a single bond. The distance between two chlorine atoms in a chlorine molecule, for example, is ${\text{198 pm}}{\text{.}}$ Thus, the covalent radius of chlorine is,
\[{\text{Covalent radius of chlorine}} = \dfrac{{198}}{2} \\ = 99{\text{ pm}}\]
The radius of an ion is referred to as its ionic radius (cation or anion). The distances between the cations and anions in ionic crystals can be used to compute the ionic radii. Because a cation is generated by removing an electron from an atom, it has fewer electrons than the parent atom and hence has a higher effective nuclear charge. As a result, a cation is smaller than its parent. The ionic radius of ${\text{N}}{{\text{a}}^ + }$ is ${\text{95 pm,}}$ while the atomic radius of the ${\text{Na}}$ atom is ${\text{186 pm}}{\text{.}}$ An anion, on the other hand, is larger than its parent atom. This is due to the fact that an anion has the same nuclear charge as the parent atom but contains more electrons, resulting in higher electron repulsion and a drop in the effective nuclear charge. The ionic radius of the ${{\text{F}}^ - }$ ion, for example, is ${\text{136 pm,}}$ while the atomic radius of the ${\text{F}}$ atom is ${\text{64 pm}}{\text{.}}$
How does atomic radius vary in a period and in a group? How do you explain the variation?
Ans :
Across a period, the atomic radius decreases from left to right. Because the outer electrons are present in the same valence shell during a period and the atomic number increases from left to right across a period, the effective nuclear charge increases. As a result, electrons become more attracted to the nucleus.
The atomic radius, on the other hand, tends to rise as you progress through the groups. This is due to the fact that as the primary quantum number $\left( n \right)$ decreases, the distance between the nucleus and valence electrons rises.