Question 1

What do you understand by (i) electron-deficient, (ii) electron-precise, and (iii) electron-rich compounds of hydrogen?

Accepted Answer

(i) Electron deficient compounds of hydrogen do not have sufficient number 
of electrons to form normal covalent bonds. Examples include hydrides of
 group 13 such as  \displaystyle BH_3, AlH_3   etc. They exist in 
polymeric forms such as  \displaystyle B_2H_6, Al_2H_6  . Thus, they 
make up their deficiency.(ii) Electron precise compounds of hydrogen contain sufficient valence 
electrons to form covalent bonds. Examples include group 14 hydrides 
 \displaystyle CH_4,SiH_4, GeH_4, SnH_4, PbH_4   etc. These compounds 
have tetrahedral shape.(iii) Electron rich compounds of hydrogen contain excess valence electrons to form covalent bonds.Examples include group 15 and group 17 hydrides such as  \displaystyle NH_3, PH_3, HCl, HBr   etc. These compounds contains lone pairs of electrons.

Question 2

Why is Hydrogen placed in group  I  of the modern periodic table ?

Accepted Answer

Hydrogen is placed in group  I  of the modern periodic table due to following reasons:- (1)  It shows outer electronic configuration similar to group  I  elements (i.e. 1s^{1} ). (2)  It readily looses its electron to form  H^{+}  ion which resembles the electropositive character of group  I  elements. (3)  It shows  +1  oxidation state like alkali i.e. group  I  elements. (4)  Hydrogen also acts as a strong reducing agent like alkali metals and also forms binary compounds with electronegative elements which resembles the group  I  elements.

Question 3

Which of the following explanation is best for not placing hydrogen with alkali metals or halogen?

Accepted Answer

The ionization energy of hydrogen is too high for group of alkali metals, but too low for halogen group.

Question 4

Among  NH_3 ,  H_2O  and  HF , which would you expect to have highest magnitude of  hydrogen bonding and why?

Accepted Answer

The electronegativity of  N, O  and  F  is much higher than the electronegativity of  H . Hence,  \displaystyle NH_3, H_2O   and   HF   forms hydrogen bonds.  F  is most electronegative and the magnitude of negative charge on  F  and positive charge on  H  is highest and thus, the  H  bonding is strongest in  HF .

Question 5

Hydrogen resembles halogens in many respects for which several factors are responsible. Of the following factors which one is the most important in this respect?

Accepted Answer

Hydrogen resembles halogens as it has similar tendency to gain a single electron to attain stable noble gas configuration. The electronic configuration of hydrogen is  1s^1 . It needs one more electron to attain stable electronic configuration of hellium, a noble gas. The electronic configuration of halogen is  ns^2np^5 . It needs one more 
electron to attain stable electronic configuration of a noble 
gas.

Question 6

Justify the position of hydrogen in the periodic table on the basis of its electronic configuration.

Accepted Answer

Hydrogen with atomic number 1 and electronic configuration  1s^1  is the first element in the periodic table. It resembles alkali metals as well as halogens. Hence, its position is anomalous. Some chemists argue that hydrogen should be placed along with alkali metals whereas other chemist argue that hydrogen should be placed with halogens.

Question 7

Electronic configuration of deuterium is _________.

Accepted Answer

Hydrogen has one proton and no neutron. Its atomic number is one and the electronic configuration is  1s^1 .Deuterium has one neutron and one proton. The mass number of deuterium is  2 . Its electronic configuration is the same as that of hydrogen,  1s^1  as it is an isotope of hydrogen.

Question 8

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Accepted Answer

Hydrogen resembles both alkali metals as well as halogens. This is because hydrogen-like alkali metals donate its' outer electron to form compounds like oxides, halides & sulfides. Also, it shares its' electron with another hydrogen atom to form a diatomic molecule.Answer: (A) Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.

Question 9

Hydrogen occupies a unique position in Modern Periodic Table.

Accepted Answer

Hydrogen has electron configuration of   1s^{1} .To become stable it can either accept to get helium configuration that is a stable configuration or it can even donate one electron. Hence it is very confusing where to place either in the metals group as it donates or in nonmetal group as it accepts an electron. Hence it occupies a unique position in the periodic table.

Question 10

Assertion (A): Hydrogen shows resemblance with alkali metals as well as halogens.Reason (R): Hydrogen exists in atomic form only at high temperature.

Accepted Answer

Hydrogen is having similarities with alkali metals and halogens in many properties because of only 1 valence electron.Hydrogen exists in atomic form at high temperatures. At normal it exists as a diatomic molecule. Both assertion and reason are true but the reason does not satisfy the assertion.Option B is correct.

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Important Questions

What do you understand by (i) electron-deficient, (ii) electron-precise, and (iii) electron-rich compounds of hydrogen?

Why is Hydrogen placed in group $I$ of the modern periodic table ?

Which of the following explanation is best for not placing hydrogen with alkali metals or halogen?

Among $N H_{3}$ , $H_{2} O$ and $H F$ , which would you expect to have highest magnitude of hydrogen bonding and why?

Hydrogen resembles halogens in many respects for which several factors are responsible. Of the following factors which one is the most important in this respect?

Justify the position of hydrogen in the periodic table on the basis of its electronic configuration.

Electronic configuration of deuterium is _________.

Hydrogen resembles both, alkali metals as well as halogens.

Hydrogen forms oxides, halides and sulphides, and exists as diatomic molecule.

Hydrogen occupies a unique position in Modern Periodic Table.

Assertion (A): Hydrogen shows resemblance with alkali metals as well as halogens.
Reason (R): Hydrogen exists in atomic form only at high temperature.

Revise with Concepts

Position of Hydrogen in the Periodic Table

Learn with Videos

Important Questions

What do you understand by (i) electron-deficient, (ii) electron-precise, and (iii) electron-rich compounds of hydrogen?

Why is Hydrogen placed in group I of the modern periodic table ?

Which of the following explanation is best for not placing hydrogen with alkali metals or halogen?

Among NH3​, H2​O and HF, which would you expect to have highest magnitude of hydrogen bonding and why?

Hydrogen resembles halogens in many respects for which several factors are responsible. Of the following factors which one is the most important in this respect?

Justify the position of hydrogen in the periodic table on the basis of its electronic configuration.

Electronic configuration of deuterium is _________.

Hydrogen resembles both, alkali metals as well as halogens.

Hydrogen forms oxides, halides and sulphides, and exists as diatomic molecule.

Hydrogen occupies a unique position in Modern Periodic Table.

Assertion (A): Hydrogen shows resemblance with alkali metals as well as halogens. Reason (R): Hydrogen exists in atomic form only at high temperature.

Why is Hydrogen placed in group $I$ of the modern periodic table ?

Among $N H_{3}$ , $H_{2} O$ and $H F$ , which would you expect to have highest magnitude of hydrogen bonding and why?

Assertion (A): Hydrogen shows resemblance with alkali metals as well as halogens.
Reason (R): Hydrogen exists in atomic form only at high temperature.