Q: Which of the following hydrides is electron deficient?

\left (BH_{3} \right ) is the chemical formula for the Boron atom. It is surrounded by 6 electrons, so it is electron deficient due to its incomplete octet. B-atom in diborane is sp^{3} hybridized. B_{2}H_{6} molecule has a total of 8 covalent bonds but only 12 electrons i.e. 6 pairs. So, it has two electron pairs less than the maximum required number for bonding, which makes it electron deficient. The answer is option D.

Q: What is hydride? How many types of hydrides are there? Explain example.

Hydrides The binary compounds of dihydrogen with oredr elements except noble gases are called HydridesThere are following types of hydrides:1. Covalent of Molecular Hydride: Dehydrogen forms molecular hydrides with most of the p- block elements. They consist of discrete covalent molecules with are held together by weak Vander Waal's forces of attraction. They have low melting and boiling point. They are volatile in naturee.g., CH_4, NH_3, H_2O and HF .These are of three types on the basis of relative number of electrons and bonds in their Lewis structure: \bullet Electron deficient hydride: Electrons of group 13 will electrons deficient hydride. They act as Lewis acids, e.g. B_2H_6 \bullet Electrons-precise hydride: All elements group 14 from electrons presise hydrides e.g, CH_4 \bullet Electrons hydride: Elements of group 15-17 from such compounds. They act as Lewis bases e.g NH_3 2. Ionic or Saline hydride: These are stoichiometic compounds of hydrogen formed with most of the s- block elements. i.e., alkali and alkaline earth metals. These hydride are crystalline, non volatile and non-conducting solid state. They have high melting and boiling points.e.e., NaH, BeH_2, MgH_2 etc.3. Metallic or Interstitial hydrides: These hydrides are formed by the reaction of dihydrogen with d- block and f- block elements. Due to small size dihydrogen in these hydride, hydrogen occupies interstices in the metal lattice producing distribution without any charge in its type. So these are known as interstitial hydrides. These are non-stoichiometric being deficient in hydrogen.e.g., scH_2, LaH_2, T_2H_2, CrH_3 etc.

Q: Among CaH_2, NH_3, NaH and B_2H_6 , which are covalent hydrides?

NH_3 and B_2H_6 are the covalent hydrides and CaH_2 and NaH are the ionic hydride. N and B form covalent hydride as they have high electronegativity and small size.

Q: What do you understand by the term non-stoichiometric hydrides? Do you expect this type of the hydrides to be formed by alkali metals? Justify your answer.

In non stoichiometric hydrides, the ratio of the metal to hydrogen is fractional and does not correspond to actual formula. Their composition varies with temperature and pressure. \displaystyle TiH_x (x=1.8\ to\ 2) and \displaystyle ZrH_x(x=1.30\ to\ 1.75) are examples of non stoichiometric hydrides. d and f block elements form such types of hydrides.Alkali metals readily lose their valence electron and act as strong reducing agents. The electrons lost by alkali metals are gained by H to form ionic hydrides in which the ratio of alkali metals to hydrogen is fixed. Hence, alkali metals form only stioichiometric hydrides.

Q: Ionic hydride reacts with water to give:

Ionic hydrides give basic solution when reacts with water. e.g. LiH+{ H }_{ 2 }O\longrightarrow \underset{base}{LiOH}+{ H }_{ 2 }\uparrow

Q: Metal hydrides are ionic, covalent or molecular in nature. Among LiH,\ NaH,\ KH,\ RbH and CsH , the correct order of increasing ionic character is:

According to Fajan’s rule, as the size of cation increases, the polarisation of anion decreases; the percentage covalent character decreases and the percentage ionic character increases.And as we move down the group, the size of elements increases .Thus, the order of atomic radii of the alkali metals is Li < Na< K< Rb< Cs .Thus, order of increasing percentage ionic character in alkali metal hydrides will be: LiH< NaH<KH< RbH<CsH

Q: What are electrons deficient and electron rich compounds of hydrogen? Give examples.

The hydrides which have tendency to accept electrons in order to make octet. Group 13 hydrides(compounds of hydrogen), mainly hydrides of Aluminium and Barium are called electron deficient hydrides. For example: BH_{3} Electron rich hydride is the type of hydride in which the number of electrons present are more than the number of electron required to make the octet. The hydrides of group 15 are electron rich. For example: NH_{3}

Question 1

Which of the following hydrides is electron-precise hydride?

Accepted Answer

Methane  CH_4  is electron-precise hydride.Diborane  B_2H_6  is electron-deficient hydrideAmmonia  NH_3  and water  H_2O  are electron-rich hydrides.Elements of group 14 form electron-precise (having required number of electrons to write the Lewis structure ) form precise hydrides.

Question 2

Elements of which of the following groups do not form hydrides?

Accepted Answer

The region of the periodic table from the group  7  to  9  is referred to as the hydride gap as they do not form hydrides. Examples of such elements are Mn, Fe, Co, Ru etc. These elements do not form hydrides on account of low affinity for hydrogen in their normal oxidation states. Hence, option C is correct.

Question 3

Arrange the following.(i)  CaH_2 ,  BeH_2  and  TiH_2  in order of increasing electrical conductance.(ii)  LiH, NaH  and  CsH  in order of increasing ionic character.(iii)  H-H, D-D  and  F-F  in order of increasing bond dissociation enthalpy.(iv)  NaH, MgH_2  and  H_2O  in order of increasing reducing property.

Accepted Answer

(i) Ionic compounds conduct electricity whereas covalent compounds does not. \displaystyle BeH_2   is a covalent hydride and does not conduct electricity.  \displaystyle CaH_2   is an ionic hydride and conducts electricity in molten state.  \displaystyle TiH_2   is metallic in nature and conducts electricity at room temperature.Hence, the increasing order of electrical conductivity is  \displaystyle BeH_2<CaH_2<TiH_2  .(ii) The ionic character of bond depends on electronegativity difference between two atoms. When the electronegativity difference is larger, the ionic character is smaller. On moving down the group of alkali metals, the electronegativity decreases from Li to Cs. Hence the ionic character increases in the order  \displaystyle LiH < NaH < CsH  .(iii) Bond dissociation energy depends on bond strength. Bond strength depends on the attractive and repulsion forces present in a molecule.Due to higher nuclear mass of  \displaystyle D_2  , the attraction between nucleus and bond pair in D-D is stronger than in H-H. This results in greater bond strength and higher bond dissociation enthalpy. Thus, the bond dissociation enthalpy of  \displaystyle D-D   is higher than that of  \displaystyle H-H  .The bond dissociation enthalpy of F-F is minimum as the repulsion between the bond pair and lone pairs of F is strong. Hence, the increasing order of bond dissociation enthalpy is  \displaystyle F-F < H-H < D-D  .(iv) NaH is an ionic hydride and can easily donate its electrons. It is most reducing.  \displaystyle MgH_2   and  \displaystyle H_2O   are covalent hydrides.  \displaystyle H_2O   has lower reducing power than  \displaystyle MgH_2   as its bond dissociation energy is higher. Hence, the increasing order of the reducing property is  \displaystyle H_2O < MgH_2 < NaH  .

Question 4

Which of the following hydrides is electron deficient?

Accepted Answer

\left (BH_{3} \right )  is the chemical formula for the
Boron atom. It is surrounded by 6 electrons, so it is electron deficient due to
its incomplete octet. B-atom in diborane is  sp^{3}  hybridized.  B_{2}H_{6} 
molecule has a total of 8 covalent bonds but only 12 electrons i.e. 6 pairs. So, it
has two electron pairs less than the maximum required number for bonding, which
makes it electron deficient.

The answer is option D.

Question 5

What is hydride? How many types of hydrides are there? Explain example.

Accepted Answer

Hydrides The binary compounds of dihydrogen with oredr elements except noble gases are called HydridesThere are following types of hydrides:1. Covalent of Molecular Hydride: Dehydrogen forms molecular hydrides with most of the  p- block elements. They consist of discrete covalent molecules with are held together by weak Vander Waal's forces of attraction. They have low melting and boiling point. They are volatile in naturee.g.,  CH_4, NH_3, H_2O  and  HF .These are of three types on the basis of relative number of electrons and bonds in their Lewis structure: \bullet  Electron deficient hydride: Electrons of group  13  will electrons deficient hydride. They act as Lewis acids, e.g.  B_2H_6 \bullet  Electrons-precise hydride: All elements group  14  from electrons presise hydrides e.g,  CH_4 \bullet  Electrons hydride: Elements of group  15-17  from such compounds. They act as Lewis bases e.g  NH_3 2. Ionic or Saline hydride: These are stoichiometic compounds of hydrogen formed with most of the  s- block elements. i.e., alkali and alkaline earth metals. These hydride are crystalline, non volatile and non-conducting solid state. They have high melting and boiling points.e.e.,  NaH, BeH_2, MgH_2  etc.3. Metallic or Interstitial hydrides: These hydrides are formed by the reaction of dihydrogen with  d- block and  f- block elements. Due to small size dihydrogen in these hydride, hydrogen occupies interstices in the metal lattice producing distribution without any charge in its type. So these are known as interstitial hydrides. These are non-stoichiometric being deficient in hydrogen.e.g.,  scH_2, LaH_2, T_2H_2, CrH_3  etc.

Question 6

Among  CaH_2, NH_3, NaH  and  B_2H_6 , which are covalent hydrides?

Accepted Answer

NH_3  and  B_2H_6  are the covalent hydrides and  CaH_2  and  NaH  are the ionic hydride. N  and  B  form covalent hydride as they have high electronegativity and small size.

Question 7

What do you understand by the term non-stoichiometric hydrides? Do you expect this type of the hydrides to be formed by alkali metals? Justify your answer.

Accepted Answer

In non stoichiometric hydrides, the ratio of the metal to hydrogen is fractional and does not correspond to actual formula. Their composition varies with temperature and pressure.  \displaystyle TiH_x (x=1.8\ to\ 2)   and  \displaystyle ZrH_x(x=1.30\ to\ 1.75)   are examples of non stoichiometric hydrides. d and f block elements form such types of hydrides.Alkali metals readily lose their valence electron and act as strong reducing agents. The electrons lost by alkali metals are gained by H to form ionic hydrides in which the ratio of alkali metals to hydrogen is fixed. Hence, alkali metals form only stioichiometric hydrides.

Question 8

Ionic hydride reacts with water to give:

Accepted Answer

Ionic hydrides give basic solution when reacts with water. e.g. LiH+{ H }_{ 2 }O\longrightarrow \underset{base}{LiOH}+{ H }_{ 2 }\uparrow

Question 9

Metal hydrides are ionic, covalent or molecular in nature. Among  LiH,\ NaH,\ KH,\ RbH  and   CsH , the correct order of increasing ionic character is:

Accepted Answer

According to Fajan’s rule, as the size of cation increases, the polarisation of anion decreases; the percentage covalent character decreases and the percentage ionic character increases.And as we move down the group, the size of elements increases .Thus, the order of  atomic radii of the alkali metals is  Li < Na< K< Rb< Cs .Thus, order of increasing percentage ionic character in alkali metal hydrides will be:         LiH< NaH<KH< RbH<CsH

Question 10

What are electrons deficient and electron rich compounds of hydrogen? Give examples.

Accepted Answer

The hydrides which have tendency to accept electrons in order to make octet. Group 13 hydrides(compounds of hydrogen), mainly hydrides of Aluminium and Barium are called electron deficient hydrides. For example:   BH_{3}   Electron rich hydride is the type of hydride in which the number of electrons present are more than the number of electron required to make the octet. The hydrides of group 15 are electron rich. For example:   NH_{3}

Revise with Concepts

Hydrides - Ionic, Covalent and Metallic

Learn with Videos

Quick Summary With Stories

Preparation and Characteristics of Ionic Hydrides

Uses of Ionic Hydrides

Covalent Hydrides and their Preparation

Properties of Covalent Hydrides

Metallic Hydrides

Important Questions

Which of the following hydrides is electron-precise hydride?

Elements of which of the following groups do not form hydrides?

Which of the following hydrides is electron deficient?

What is hydride? How many types of hydrides are there? Explain example.

Among $C a H_{2}, N H_{3}, N a H$ and $B_{2} H_{6}$ , which are covalent hydrides?

What do you understand by the term non-stoichiometric hydrides? Do you expect this type of the hydrides to be formed by alkali metals? Justify your answer.

Ionic hydride reacts with water to give:

Metal hydrides are ionic, covalent or molecular in nature. Among $L i H, N a H, K H, R b H$ and $C s H$ , the correct order of increasing ionic character is:

What are electrons deficient and electron rich compounds of hydrogen? Give examples.

Revise with Concepts

Hydrides - Ionic, Covalent and Metallic

Learn with Videos

Quick Summary With Stories

Preparation and Characteristics of Ionic Hydrides

Uses of Ionic Hydrides

Covalent Hydrides and their Preparation

Properties of Covalent Hydrides

Metallic Hydrides

Important Questions

Which of the following hydrides is electron-precise hydride?

Elements of which of the following groups do not form hydrides?

Which of the following hydrides is electron deficient?

What is hydride? How many types of hydrides are there? Explain example.

Among CaH2​,NH3​,NaH and B2​H6​, which are covalent hydrides?

What do you understand by the term non-stoichiometric hydrides? Do you expect this type of the hydrides to be formed by alkali metals? Justify your answer.

Ionic hydride reacts with water to give:

Metal hydrides are ionic, covalent or molecular in nature. Among LiH, NaH, KH, RbH and CsH, the correct order of increasing ionic character is:

What are electrons deficient and electron rich compounds of hydrogen? Give examples.

Among $C a H_{2}, N H_{3}, N a H$ and $B_{2} H_{6}$ , which are covalent hydrides?

Metal hydrides are ionic, covalent or molecular in nature. Among $L i H, N a H, K H, R b H$ and $C s H$ , the correct order of increasing ionic character is: