Mendeleev's Periodic Table Questions in English

(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.

(B) Mendeleev's Periodic Law states that the properties of elements are a periodic function of their atomic masses.
Therefore,Mendeleev arranged the elements in the periodic table in the order of increasing atomic masses.

(C) Mendeleev predicted the existence of several elements that had not been discovered at that time.
He named them by prefixing a Sanskrit numeral 'Eka' (one) to the name of the preceding element in the same group.
For example,he named 'Eka-boron' (Scandium),'Eka-aluminium' (Gallium),and 'Eka-silicon' (Germanium).
Therefore,Germanium is the element that was discovered later and placed in the gap left by Mendeleev.

(C) Eka-aluminium is the name given by Mendeleev to the element Gallium $(Ga)$.
Gallium belongs to Group $13$ of the periodic table.
Elements in Group $13$ have a valency of $3$.
Oxygen has a valency of $2$.
When an element $E$ with valency $3$ reacts with oxygen (valency $2$),the formula of the oxide is formed by crossing the valencies.
Thus,the formula becomes $E_2O_3$.

(B) Mendeleev's primary criterion for arranging elements was to group elements with similar chemical properties together in the same column or group.
Even though cobalt $(58.93 \ amu)$ has a higher atomic mass than nickel $(58.71 \ amu)$,Mendeleev placed cobalt before nickel because cobalt shows chemical properties similar to rhodium and iridium,while nickel shows properties similar to palladium and platinum.
Therefore,to maintain the periodicity of properties,he prioritized chemical similarity over the strict increasing order of atomic masses.

(A) Mendeleev predicted the existence of several elements that were not discovered at that time.
He named the element below silicon as Eka-silicon,which was later identified as Germanium $(Ge)$. Since silicon is in group $14$,its chloride is $SiCl_4$. Therefore,the formula for the chloride of Eka-silicon is $GeCl_4$.
He named the element below aluminium as Eka-aluminium,which was later identified as Gallium $(Ga)$. Since aluminium is in group $13$,its chloride is $AlCl_3$. Therefore,the formula for the chloride of Eka-aluminium is $GaCl_3$.
Thus,the formulae are $GeCl_4$ and $GaCl_3$.

(A) The element that replaced Eka-silicon is Germanium $(Ge)$ and the element that replaced Eka-aluminium is Gallium $(Ga)$.
$(b)$ In the Modern Periodic Table,Germanium $(Ge)$ belongs to Group $14$ and Period $4$. Gallium $(Ga)$ belongs to Group $13$ and Period $4$.

(A) Mendeleev's Eka-silicon is known as Germanium $(Ge)$,which is a metalloid. Eka-aluminium is known as Gallium $(Ga)$,which is a metal.
$(b)$ Gallium $(Ga)$ belongs to Group $13$ of the periodic table,so it has $3$ valence electrons. Germanium $(Ge)$ belongs to Group $14$ of the periodic table,so it has $4$ valence electrons.

(A) The group of elements that could be placed in Mendeleev's Periodic Table without disturbing the original order is the Noble gases.
Reason:
$1$. Mendeleev's periodic law states that the properties of elements are a periodic function of their atomic masses.
$2$. Noble gases are chemically inert and possess very low reactivity due to their stable electronic configuration.
$3$. Because they do not react with other elements,they could be placed in a separate group (Group $0$ or $VIII$) without requiring any changes to the positions of the existing elements in the table.

(N/A) Mendeleev examined the relationship between the atomic masses of elements and their physical and chemical properties.
Among chemical properties,he concentrated on the compounds formed by elements with oxygen and hydrogen (oxides and hydrides).
He selected these two elements because they are very reactive and formed compounds with most elements.
He wrote down the properties of each element on separate cards and grouped together elements with similar properties.
He observed that most of the elements got arranged in the periodic table in the order of increasing atomic masses.
Based on this,he formulated the Periodic Law,which states that the properties of elements are a periodic function of their atomic masses.

(N/A) Mendeleev's Periodic Law states that the physical and chemical properties of elements are a periodic function of their atomic masses.

(N/A) Mendeleev predicted the existence of several elements that had not been discovered at the time he proposed his periodic table. He named them $Eka-boron$,$Eka-aluminium$,and $Eka-silicon$. Later,these elements were discovered and named as follows:
$1$. $Eka-boron$ was discovered as $Scandium$ $(Sc)$.
$2$. $Eka-aluminium$ was discovered as $Gallium$ $(Ga)$.
$3$. $Eka-silicon$ was discovered as $Germanium$ $(Ge)$.
Therefore,any two of these,such as $Gallium$ and $Germanium$,are correct answers.

(N/A) The anomalies of Mendeleev's periodic table that were resolved by the modern periodic law are as follows:
$(i)$ Position of Hydrogen: Mendeleev could not assign a fixed position to hydrogen because it shows properties of both alkali metals and halogens. The modern periodic law places it based on atomic number.
$(ii)$ Position of Isotopes: Isotopes have the same atomic number but different atomic masses. Mendeleev's table was based on atomic mass,leading to confusion. The modern periodic law,based on atomic number,places all isotopes of an element in the same position.
$(iii)$ Anomalous Pairs: In Mendeleev's table,some elements with higher atomic masses were placed before elements with lower atomic masses (e.g.,Cobalt and Nickel). The modern periodic law,based on atomic number,correctly places these elements in increasing order of their atomic numbers.

(N/A) Classification of elements helps in:
$(i)$ Systematic study of the properties of elements.
$(ii)$ Making it easier to understand and remember the properties of elements.
$(b)$ The two criteria used by Mendeleev were:
$(i)$ Increasing order of atomic mass.
$(ii)$ Similarity in the chemical properties of the elements.
$(c)$ Mendeleev left gaps in his periodic table for elements that were yet to be discovered,such as gallium and germanium.
$(d)$ There was no mention of noble gases like helium,neon,and argon because they were not known at that time and were discovered much later.
$(e)$ According to Mendeleev's periodic table,$Cl-35$ and $Cl-37$ should be placed in different positions because the basis of classification was the increasing order of atomic masses. However,since their chemical properties are identical,they are placed in the same position in the modern periodic table,which is based on atomic number.

(C) When Dmitri Mendeleev started his work on the classification of elements,there were $63$ elements known to science.
He used these $63$ elements to formulate his Periodic Law,which states that the properties of elements are a periodic function of their atomic masses.

(C) Eka-aluminium was the name given by Mendeleev to the element Gallium $(Ga)$.
Gallium belongs to Group $13$ of the periodic table,similar to Aluminium $(Al)$.
Elements in Group $13$ have a valency of $3$.
When an element $E$ with a valency of $3$ reacts with Oxygen (which has a valency of $2$),it forms an oxide with the formula $E_2O_3$ according to the criss-cross method of chemical formula writing.
Therefore,Eka-aluminium forms an oxide of the type $E_2O_3$.

(B) Mendeleev predicted the existence of several elements that had not been discovered at that time.
He named them by prefixing a Sanskrit numeral 'Eka' to the name of the preceding element in the same group.
For example,he named 'Eka-silicon' to the element that was discovered later and named 'Germanium'.
Therefore,Germanium is the element that found a place in the periodic table later.

(TRUE) The statement is True. Mendeleev's periodic law states that the properties of elements are a periodic function of their atomic masses. He arranged the elements in increasing order of their atomic masses and observed that elements with similar physical and chemical properties repeat after regular intervals.

(FALSE) The statement is False. It was Henry Moseley,not Dmitri Ivanovich Mendeleev,who demonstrated in $1913$ that the atomic number of an element is a more fundamental property than its atomic mass. Mendeleev's periodic law was based on atomic mass.