Textbook - Periodic Classification of Elements Questions in English

(N/A) Only one triad of Dobereiner's triads exists in the columns of Newlands' octaves. The triad formed by the elements $Li$, $Na$, and $K$ of Dobereiner's triads also occurred in the columns of Newlands' octaves.
Dobereiner's triads:
$\begin{matrix} Li & Ca & Cl \\ Na & Sr & Br \\ K & Ba & I \end{matrix}$
Newlands' octaves:

$H$	$Li$	$Be$	$B$	$C$	$N$	$O$
$F$	$Na$	$Mg$	$Al$	$Si$	$P$	$S$
$Cl$	$K$	$Ca$	$Cr$	$Ti$	$Mn$	$Fe$
$Co$ and $Ni$	$Cu$	$Zn$	$Y$	$In$	$As$	$Se$
$Br$	$Rb$	$Sr$	$Ce$ and $La$	$Zr$	-	-

(A) The main limitation of Dobereiner's classification was that he could not arrange all the elements known at that time into groups of triads based on their chemical properties.
Only a limited number of elements could be grouped into triads,making the system insufficient for the classification of all elements.

(D) Limitations of Newlands' Law of Octaves:
$(i)$ It was not applicable throughout the entire arrangement. It was applicable only up to calcium. The properties of the elements listed after calcium did not show resemblance to the properties of the elements above them.
$(ii)$ Elements discovered after Newlands' time did not follow the Law of Octaves.
$(iii)$ The position of cobalt and nickel in the same group as fluorine $(F)$ and chlorine $(Cl)$,which have different properties,could not be explained.
$(iv)$ The placement of iron far away from cobalt and nickel,despite iron having similar properties to them,could not be explained.

(A) $K$ is in group $I$. Therefore,the oxide formula is $K_2O$.
$C$ is in group $IV$. Therefore,the oxide formula is $CO_2$.
$Al$ is in group $III$. Therefore,the oxide formula is $Al_2O_3$.
$Si$ is in group $IV$. Therefore,the oxide formula is $SiO_2$.
$Ba$ is in group $II$. Therefore,the oxide formula is $BaO$.

(N/A) Mendeleev predicted the existence of several elements that had not been discovered at that time. He named them Eka-boron,Eka-aluminium,and Eka-silicon. These were later discovered and named as Scandium $(Sc)$,Gallium $(Ga)$,and Germanium $(Ge)$ respectively. Therefore,besides Gallium,the other two elements are Scandium and Germanium.

(B) $Mendeleev$'s periodic table was based on the observation that the properties of elements are a periodic function of their atomic masses.
This means that if elements are arranged in the increasing order of their atomic masses,then their properties get repeated after regular intervals.
He also considered the chemical properties of elements,specifically the formation of hydrides and oxides,to classify them.

(N/A) Noble gases are chemically inert elements because they have a stable electronic configuration with a complete octet (or duplet in the case of Helium).
Their chemical properties are significantly different from all other elements in the periodic table.
Due to their unique stability and lack of reactivity,they are placed in a separate group,known as Group $18$.

(N/A) Mendeleev was unable to assign a fixed position to hydrogen and isotopes in his periodic table.
In Mendeleev's periodic table,the increase in atomic mass of the elements was not always regular from one element to the next.
It was believed that a more fundamental property than atomic mass could explain periodic properties in a better manner.
Henry Moseley demonstrated that the atomic number of an element is a more fundamental property than its atomic mass for explaining periodic properties.
By arranging elements in the increasing order of their atomic numbers,the Modern Periodic Table successfully resolved the anomalies found in Mendeleev's Periodic Table.

(N/A) Calcium $(Ca)$ and strontium $(Sr)$ are expected to show chemical reactions similar to magnesium $(Mg)$.
This is because the number of valence electrons $(2)$ is the same in all these three elements.
Since chemical properties of elements are determined by their valence electrons,elements with the same number of valence electrons exhibit similar chemical reactions.

(N/A) Lithium $(Li)$,sodium $(Na)$,and potassium $(K)$ have a single electron in their outermost shells.
$(b)$ Magnesium $(Mg)$ and calcium $(Ca)$ have two electrons in their outermost shells.
$(c)$ Neon $(Ne)$,argon $(Ar)$,and xenon $(Xe)$ have filled outermost shells.

(N/A) Yes. The atoms of all three elements—$lithium$,$sodium$,and $potassium$—have one electron in their outermost shells. This similarity in their electronic configuration (all belong to Group $1$) is the reason they exhibit similar chemical properties,such as reacting with water to release hydrogen gas.

(C) Both helium $(He)$ and neon $(Ne)$ are noble gases.
Their atoms have completely filled outermost shells.
Helium has a stable duplet in its $K$ shell ($2$ electrons),while neon has a stable octet in its $L$ shell ($8$ electrons).
This stable electronic configuration makes them chemically unreactive or inert.

(A) The first ten elements of the Modern Periodic Table are Hydrogen $(H)$,Helium $(He)$,Lithium $(Li)$,Beryllium $(Be)$,Boron $(B)$,Carbon $(C)$,Nitrogen $(N)$,Oxygen $(O)$,Fluorine $(F)$,and Neon $(Ne)$.
Among these,Lithium $(Li)$ and Beryllium $(Be)$ are classified as metals,while the others are non-metals or metalloids.

(D) Metallic character increases as we move from right to left across a period and decreases as we move from top to bottom down a group.
Among the given elements,$Be$ (Beryllium) is located in Group $2$ and Period $2$.
$Ga$,$Ge$,$As$,and $Se$ are located in Period $4$.
Since $Be$ is in the second period and is an alkaline earth metal located at the far left compared to the other elements listed,it exhibits the highest metallic character.

(C) The correct answer is $C$.
When moving from left to right across the periods of the periodic table,the effective nuclear charge increases and the atomic size decreases.
This makes it harder for atoms to lose electrons,meaning their metallic character decreases and non-metallic character increases.
Therefore,the statement that 'atoms lose their electrons more easily' is incorrect.

(D) The formula $XCl_2$ indicates that the element $X$ has a valency of $2$ (since chlorine has a valency of $1$). Elements that form chlorides with the formula $XCl_2$ are typically alkaline earth metals belonging to Group $2$ of the Periodic Table. Among the given options,$Mg$ (Magnesium) belongs to Group $2$. Therefore,$X$ would most likely be in the same group as $Mg$.

(N/A) Neon $(Ne)$ has two shells,$K$ and $L$,both of which are completely filled with electrons ($2$ electrons in $K$ shell and $8$ electrons in $L$ shell,total $10$ electrons).
$(b)$ Magnesium $(Mg)$ has the electronic configuration $2, 8, 2$ (total $12$ electrons).

(N/A) Silicon $(Si)$ has a total of three shells,with four electrons in its valence shell ($2$ electrons in $K$ shell,$8$ electrons in $L$ shell,and $4$ electrons in $M$ shell).
$(b)$ Boron $(B)$ has a total of two shells,with three electrons in its valence shell ($2$ electrons in $K$ shell and $3$ electrons in $L$ shell).
$(c)$ Carbon $(C)$ has twice as many electrons in its second shell as in its first shell ($2$ electrons in $K$ shell and $4$ electrons in $L$ shell).

(A) All elements in the same group (column) of the Periodic Table exhibit similar chemical properties because they have the same number of valence electrons.
Boron $(B)$ belongs to Group $13$ and has $3$ valence electrons.
Therefore,all elements in this column share the same number of valence electrons $(3)$ and consequently possess a valency of $3$.

(B) All elements in the same column (group) as fluorine belong to Group $17$ (the halogens).
Elements in the same group have the same number of valence electrons.
Fluorine has $7$ valence electrons,so all elements in this group also have $7$ valence electrons.
Consequently,they all exhibit similar chemical properties and have a valency of $1$.

(B) The atomic number is the sum of the electrons in all shells: $2 + 8 + 7 = 17$. Thus,the atomic number is $17$.
$(b)$ Elements with the same number of valence electrons exhibit similar chemical properties. The given element has $7$ valence electrons. Among the choices,$F(9)$ has an electronic configuration of $2, 7$,meaning it also has $7$ valence electrons. Therefore,it is chemically similar to $F(9)$.

$A$ is a non-metal because it belongs to Group $17$, which consists of halogens, and all halogens are non-metals.
$(b)$ $C$ is less reactive than $A$. In Group $17$ (halogens), the reactivity of elements decreases as we move down the group because the atomic size increases and the tendency to gain an electron decreases.

(N/A) will be smaller in size than $B$. As we move from left to right across a period,the nuclear charge increases,which pulls the electrons closer to the nucleus,resulting in a decrease in atomic size.
$(b)$ $A$ will form an anion. Since $A$ belongs to Group $17$,it has $7$ valence electrons and needs one more electron to complete its octet,thus it gains an electron to form a negatively charged ion (anion).

(A) The electronic configurations of Nitrogen $(N)$ and Phosphorus $(P)$ are as follows:

Element	Electronic Configuration $(K, L, M)$
Nitrogen $(Z=7)$	$2, 5$
Phosphorus $(Z=15)$	$2, 8, 5$

Nitrogen is more electronegative than phosphorus.
Reasoning:
$1$. Electronegativity is the tendency of an atom to attract a shared pair of electrons towards itself.
$2$. As we move down a group in the Periodic Table,the number of electron shells increases.
$3$. In Nitrogen,the valence electrons are in the $L$ shell (closer to the nucleus),whereas in Phosphorus,they are in the $M$ shell (further from the nucleus).
$4$. Due to the increased distance from the nucleus and increased shielding effect,the effective nuclear charge experienced by the valence electrons decreases as we move down the group.
$5$. Consequently,the ability to attract electrons decreases,making Nitrogen more electronegative than Phosphorus.

(N/A) The position of an element in the Modern Periodic Table is determined by its electronic configuration:
$1$. The number of valence electrons determines the group number. Elements with the same number of valence electrons are placed in the same group (column).
$2$. The number of shells occupied by electrons determines the period number. Elements in the same period have the same number of electron shells.
$3$. As we move across a period,the number of valence electrons increases by one,while the number of shells remains constant.

(A) Calcium $(Ca)$ has an atomic number of $20$ and its electronic configuration is $2, 8, 8, 2$. It belongs to Group $2$ of the periodic table.
Elements in the same group have the same number of valence electrons and exhibit similar chemical properties.
- Atomic number $12$ (Magnesium,$Mg$): Electronic configuration $2, 8, 2$. It has $2$ valence electrons and belongs to Group $2$.
- Atomic number $38$ (Strontium,$Sr$): Electronic configuration $2, 8, 18, 8, 2$. It has $2$ valence electrons and belongs to Group $2$.
Therefore,elements with atomic numbers $12$ and $38$ have physical and chemical properties resembling calcium.

(N/A)

Mendeleev's Periodic Table	Modern Periodic Table
$1$. Elements are arranged in the increasing order of their atomic masses.	$1$. Elements are arranged in the increasing order of their atomic numbers.
$2$. There are a total of $7$ groups and $6$ periods.	$2$. There are a total of $18$ groups and $7$ periods.
$3$. Elements with similar properties were placed in the same group.	$3$. Elements with the same number of valence electrons are placed in the same group.
$4$. The position of hydrogen was ambiguous.	$4$. Hydrogen is placed in group $1$ above alkali metals.
$5$. No clear distinction between metals and non-metals.	$5$. Metals are on the left and non-metals are on the right.