21 Chemistry -- Chemical Bonding and Shapes of Molecules

Why do compounds having hydrogen bonding have high melting and boiling points?

Why do compounds having hydrogen bonding have high melting and boiling points?

2 Answers

The compounds having hydrogen bonding show abnormally high melting and boiling points. The high melting and boiling point of the compound containing hydrogen bonds is due to the fact that some extra energy is needed to break these bonds.

· The unusually high boiling point of hydrogen fluoride among the halogen acid is due to the existence of hydrogen bonding.

· H₂O is a liquid whereas H₂S, H₂Se and H₂Te are all gases at ordinary temperature. In water, hydrogen bonding causes linkages in the water molecules which result in the boiling point of water is more than that of the other compounds.

· Ammonia has a higher boiling point than PH₃ because there is hydrogen bonding in NH₃ but not in PH₃.

· Ethanol has a higher boiling point than diethyl ether because there is hydrogen bonding in the ethanol.

Compounds with hydrogen bonding tend to have higher melting and boiling points because the hydrogen bonding leads to stronger intermolecular forces. Intermolecular forces are the attractive forces between molecules, and they affect the physical properties of a substance, including melting and boiling points.

Hydrogen bonding is a particularly strong type of intermolecular force that occurs when a hydrogen atom is bonded to a highly electronegative atom such as nitrogen, oxygen, or fluorine. The electronegative atom attracts electrons in the bond towards itself, creating a partial negative charge on the electronegative atom and a partial positive charge on the hydrogen atom. These partial charges create a dipole, and the dipoles of neighboring molecules can attract each other through hydrogen bonding.

The hydrogen bonds are much stronger than the typical van der Waals forces, which are the intermolecular forces between non-polar molecules. This leads to a higher amount of energy required to break these bonds, which results in higher melting and boiling points for compounds with hydrogen bonding.

For example, water (H2O) has a boiling point of 100°C, which is much higher than the boiling point of a similar molecule like hydrogen sulfide (H2S), which has no hydrogen bonding and boils at -60°C. Similarly, ammonia (NH3) has a boiling point of -33°C, while its non-hydrogen bonded counterpart, phosphine (PH3), boils at -87°C. The difference in boiling points is due to the presence or absence of hydrogen bonding.

Which orbital is non directional?

S orbitalis non directional in nature.
They are non directional because they are spherical in shape and probability of finding electrons at a particular distance from the nucleus is same in all directions.

Why is benzene molecule non polar whereas chlorobenzene is polar? Give reason.

In benzene molecule, carbon and carbon bond can't have polarity because there is not any electronegativity difference and the carbon hydrogen is also not much polar because the electronegativity difference is almost zero and also the small pull due to small difference in Electronegativity is balanced due to even pull from all directions.

In chlorobenzene the electronegativity difference between carbon and chlorine is very high so, it is polar.

(to compare polarity first check electronegativity...

Draw the orbital picture of following molecules: Methane (CH4)

Carbon has two half-filled orbitals in ground state (1s², 2s², 2px¹2py¹, 2pz⁰). It has four half-filled orbitals in excited state since one electron is promoted from 2s to empty 2p orbital during chemical combination (1s², 2s², 2px¹2py¹, 2pz⁰)

Now one 2s and three 2p orbitals undergo sp3 hybridization to form four sp3 hybrid orbitals of equivalent energy and identical shape and size which takes tetrahedral geometry with bond angle 109.28º.

Each half filled sp³hybrid orbital of carbon atom...

Draw the orbital structure of Ethane

Each carbon has four half-filled orbitals in excited state since one electron is promoted from 2s to empty 2p orbital during chemical combination. Now, one 2s and three 2p orbitals undergo sp3 hybridization to form four sp3 hybrid orbitals of equivalent energy and identical shape which take tetrahedral geometry with bond angle 109.28.

One half filled sp3 hybrid orbital of one carbon atom overlaps with half-filled sp3 orbital of another carbon atom head-to-head forming a carbon-to-carbon sigma...

Draw the orbital picture of Ethene

Each carbon has two half-filled orbitals in ground state (1s², 2s², 2px¹2py^1,2pz⁰). It has four half-filled orbitals in excited state since one electron is promoted from 2s to empty 2p orbital during chemical combination (1s², 2s², 2px¹2py^1,2pz⁰).

Now, one 2s and two 2p orbitals undergo sp²hybridization to form three sp²hybrid orbitals of equivalent energy and identical shape and size which take trigonal planar geometry with bond angle 120º. Unhybridized 2pz half-filled orbital remains...

Draw the orbit structure of Ethyne

Each carbon has two half-filled orbitals in ground state (1s², 2s², 2p_x¹2p_y¹, 2p_z⁰). It has four unpaired

electrons in excited state since one electron is promoted from 2s to empty 2p orbital during chemical reaction

(1s², 2s², 2p_x¹2p_y¹, 2p_z⁰).. i. e.

Now, one 2s and one 2p orbitals undergo sp hybridization to form two sp hybrid orbitals of equivalent energy and identical shape and size which take linear geometry with bond angle 180º. Unhybridized 2p_yand 2p_zorbitals remain perpendicular to...

What is the main cause of chemical combination? List the assumptions of electronic theory of valancy.

Atoms of elements other than noble gas have unstable electronic configuration (outermost shell is incomplete). They can lose, gain or share electrons and are chemically active.
The tendency of atoms of various elements to acquire stable configuration of the nearest noble gasis the cause of chemical combination.

The postulates of Electronic Valence Theory are:

The valence electrons take part in the formation of a covalent bond.
Atoms with 8 electrons in their valence shell are most stable....

Define the following terms: a). Electronic theory of valency b). core electrons c). Octet rule d). octet e). duplet f). Valency g). chemical bond ...

a) Electronic theory of valency: It is a theory explaining the combining capacity of an element based on the number of electrons present in the valence (outermost or ultimate) shell of an atom of an element.

b) Core electrons: All the electrons present in other than the ultimate shell of an atom of an element are called core electrons.

c) Octet rule: An octet rule is defined as a general rule according to which elements tend to have eight electrons in their valence shell in order to attain a...

The ionic bond between Na+ and Cl- resulting ionic molecule NaCl is stable. Why?

NaCl is ionic compounds so it is soluble in polar solvent. Water is a polar solvents, therefore, it can rupture the ionic bond between positive (Na⁺)and negative ( Cl^-) ions of the NaCl as a result of ion- dipole interaction. In other words, the ions of the NaCl gets hydrated.

The attractive force which binds oppositely charged ions acts equally in all directions in case of the ionic compounds. Therefore, ionic compounds are non- directional in nature.

Write the conditions for electrovalency? List the general properties of electrovalent bond.

Following are the conditions for electrovalency:

Combination of Metal and Non-metal
Metal should have low Ionization Energy
Non-metal should have high Electron Affinity
Large size of cations and Small size of anions

Following are some of the properties of Electrovalent compounds:

In room temperature, they are generally solids.
Usually, they have high Boiling point and high Melting point.
They are good conductors of electricity in their molten or fused state due to the presence of free ions.
...

Ionic compounds usually have high melting and boiling points, Why?

Ionic compounds are formed by the transfer of electrons between two atoms that creates charge in them. The compounds are held together by strong electrostatic forces of attraction between oppositely charged ions. These compounds have high melting points and high boiling pointsbecause of the large amounts of energy needed to break the many strong bonds.

Why does NaCl dissolve in water ? And why are the ionic bonds non directional?

At the molecular level, salt dissolves in water due to the fact that both water and salt compounds are polar, with positive and negative charges on opposite sides in the molecule.

The positively-charged side of the water molecules are attracted to the negatively-charged chloride ions and the negatively-charged side of the water molecules are attracted to the positively-charged sodium ions.

Also, ionic bonds are non directional in nature since they are arranged in a lattice structure where every...

Draw the Lewis structure of : a). KNO3 b). P2O3

a). KNO3

b). P2O3

Sodium chloride is a better conductor of electricity in a molten condition than in the solid state . Why?

Sodium Chloride conducts electricity due to free ions. In solid state, the ions are strongly bonded to the oppositely charged ions to form compact molecules, probhibiting their free movement. However, in molten state, these ions are free to move and can easily conduct electricity.

Define covalent bond and covalency . Write the conditions for covalency .

Covalent bond is defined as the bond existing between two atoms formed by the mutual sharing of electrons by the both atoms.

Covalency is the meausre of number of valence electrons that can be actively shared by an atom in forming a covalent bond.

The conditions for forming a covalent bond are as follows:

Combining elements should have same or comparable values of Electronegativity
Elements must have enough electrons in their valence shell (usually 5,6, or 7) in order to form a stable compound...

Draw a dot and cross diagram and displayed formulae for: i). CH4 ii). H2O iii). NH3 iv). C2H2

1. CH₄

2. H₂O

-------->

3. NH₃

------>

Why covalent compounds have low melting and boiling points? And why covalent bond is directional in character?

Covalent compouns are linked together by covalent force of attraction due to which there exists less force of attraction between the binding molecules. As a result, less energy is required to break this bond. As a result, they have low melting and boiling point.

Covalent bonds are directional in nature because they are formed due to the overlapping of orbitals of two or more atoms that arrange each other in a way to maintain minimum repulsion and ensure maximum stability.

Define : a). coordinate covalent bond b). coordinate compound c). coordinate bond

Coordinate covalent bond: A bond formed containing both coordinate and covalent bond is defined as coordinate covalent bond.

Coordinate covalent compound: A compound possesing both coordinate and covalent bond is defined as coordinate covalent compound.

Coordinate bond:A bond formed when an electron-rich atom donates one or more lone pair of electrons to the acceptor atom is defined as coordinate bond. In this type of bond, there is no mutual sharing of electrons. The atom which gives electrons...

Compare ionic , covalent and coordinate covalent bond.

Write the formula related to formal charge(F.C) of an atom? Give the Lewis structure of (NH4)SO4 .

The formal charge of an atom isthe difference between the number of valence electrons of that atom in the free state and the number of electrons given to that element in Lewis structure.

It is given by

Ammonium sulfate

Write the Lewis structure of: H2O2KNO3 HCO3-NH4+

H2O2

2. KNO3

3.HCO3-

4. NH₄-

Define resonance and resonating structures. Write the rules to indicate the phenomenon of resonance. Also write the characteristics of resonance.

Resonance isa way of describing delocalized electrons within certain molecules or polyatomic ions where the bonding cannot be expressed by a single Lewis formula.

A molecule or ion with such delocalized electrons is represented by several resonance structures. Resonance structures represent different ways of placing electrons on the atoms in a molecule's Lewis dot structure.

It is possible to write more than one equivalent resonance structure for a molecule or ion,the actual structure is the...

What does VSEPR theory explain? write its postulates.

The VSEPR theory explains that the approximate shape of the molecule can be predicted from the number of electron pairs in the valence shell of the central atom.

The postulates of the VSEPR theory are listed below:

In polyatomic molecules one of the constituent atoms is the central atom to which all other atoms are linked.
The total number of valence shell electron pairs (lone pair and bond pair) decides the shape of the molecule.
The electron pairs are oriented in a way that electrostatic...

State pauli exclusion principle. Describe valence bond theory with its postulates.

Wolfgang Pauli in 1925, put forward a principle that restrict some of the values of quantum numbers of electrons in an atom. Pauli's exclusion principle states," no two electrons in an atom can all the four quantum numbers same." In other word if three of the quantum numbers for two electrons in an atom are identical, the fourth quantum number for the two electrons should differ.

Heitler and London in 1927 developed valence bond theory based on quantum mechanical model of an atom. According to...

What is hybridization? Explain its types.

Hybridization is defined as the process of formation of degenerate hybrid orbitals by the inter-mixing of atomic orbitals of comparable energy levels. This concept was introduced to strengthen the Valence Bond Theory.

Following are the types of hybridization:

sp hybridization:

In this hybridization, one s-orbital and one p-orbital combine together to form two sp hybrid orbitals. Each hybrid orbital has 50% s-character and 50% p-character.

sp2 hybridization:

In this hybridization, one s-orbital and...

Compare sigma bond and pi bond.

Sigma bond is stronger than Pi bond.

Following are the major differences between pi bond and sigma bond:

Sigma Bond	Pi Bond
It is formed due to the head-on overlapping of combining orbitals.	It is formed due to the lateral or sideways overlapping of combining orbitals.
It is stronger than pi bond.	It is weaker than sigma bond.
Sigma bond can form independently.	Pi bond is formed only after the formation of sigma bond.
Free rotation is possible.	Free rotation is not possible.

What is bond length ? Explain factors affecting bond length.

Bond length is defined as the average distance between the nuclei of two bonded atoms in a molecule.

Bolnd length depends upon the Electronegativity difference of combining atoms, Atomic size of combining atoms, Nature of Hybridization and Type of bond.

Molecule with higher EN difference have shorter bond length.
Molecule whose constituent atoms are larger in size has larger bond length.
Molecules with sp hybridization have shorter bond lengths than those with sp2 and sp3 hybrization.
Multiple...

Define dipole moment. Explain factors affecting dipole moment.

Dipole moment is the product of magnitude of the charge (q) and the distance between the centre (d) of the charges is called dipole moment.

It is usually denoted byμ.

The factors affecting dipole moment are:

Polarity of molecule.
Magnitude of charge.
Geometry of molecule.

What is van der waal's forces(intermolecular forces). And what is van der waal's bond?

Intermolecular forces, often abbreviated to IMF, arethe attractive and repulsive forces that arise between the molecules of a substance. These forces mediate the interactions between individual molecules of a substance.

Van der Waals bondis weak intermolecular forces that are dependent on the distance between atoms or molecules.
It is the attraction between instantaneous dipole and induced dipole.

Define molecular solids. What is Hydrogen bond? Explain its type and also write its application

When the constituent particles of a solid are molecules, they are called molecular solids.

They are held together by either:

Van der Waal's forces
Dipole-dipole interaction
Hydrogen bonding

Hydrogen bond is the bond that exists between a hydrogen of a molecule (which is bonded with a strong electronegative atom) with another highly electronegative atom.

It may be between within a molecule, molecules of same species, or molecules of different species.

Types of hydrogen bonds are:

- Intermolecular...

Define metallic bond and write its properties.

The simultaneous electrostatic attraction between rhe kernels and the mobile electrons which holds the kernels together is called metallic bond.

It is a weak bond.

Electrons here are delocalized.

It causes metals to display the following characteristics.

1. Electrical Conductivity

2. Thermal conductivity

3. Luster

4. Malleable and ductile

Name the type of bonds which are present in ice.

The type of bond present in ice are:1. Covalent bond2. Hydrogen bond

H2O has higher boiling point than HF, though HF is more polar than H2O. Explain.

Water has a higher boiling point than HF, even though HF is more polar thanH₂O. This is because in HF, each molecule can be hydrogen bonded to two othsrs wherease in water, each molecule can be hydrogen bonded to four others. Therefore, even though HF forms some what stronger bond than water. The total strength of two hudrogen bonds to a water molecule exceeds the total strength of two hydrogen bondsin an HF molecule.

Define hybridization and explain why was it introduced?

Hybridization may be defined as the phenomenon of combining of orbitals of an atom of nearly equal energies, giving rise to entirely new orbitals equal in number to the mixing orbitals having same energy and identical shapes.

By valence bond theory, only half filled orbitals can take part in bonding.

Hybridization was introducedto explain molecular structure when the valence bond theory failed to correctly predict them.

Taking example of a CH₄molecule,

without hybridization concept, the orbitals...

2. Explain O-hydroxy Benz aldehyde and P-hydroxy Benz aldehyde, which is more soluble in water and why?

P-hydroxy benzaldehyde is more soluble in water than o-Hydroxy benzaldehyde, because P-Hydroxy benzaldehydecan form hydrogen bonds with water molecules resulting in enhanced solubility.

Lone pairs of electrons present on an atom in any molecule affect its geometry. Explain with an example.

If the central atom of a molecule has lone pairs along with bond pair of electrons, the ideal geometry is distorted to give different bond angles than expected to obtain minimum repulsion. This is because lone pair occupies more space around the central atom than the bond pair; since the lone pair is attracted by one atom only while bond pair is shared between two nuclei.Hence, repulsion of electron pairs around the central atom is in the order ofl.p--l.p > l.p--b.p. > b.p--b.p

For...

Discuss the formation of KCl and CCl4molecules on the basis of electronic theory of valency. Give any two characteristics of ionic and covalent bond.

Ans:The Electronic theory of valency states that atoms of elements(which are not noble gases) tend to acquire the nearest noble gas configuration by either transfer or sharing of electrons.
KCl is an ionic molecule formed as:19K= 2,8,8,1 17Cl = 2,8,7

Potassium donates the extra valence electron and attains stable configuration of Argon, and Positive charge. Chlorine accepts the electron and also attains the stable configuration of Argon and a negative charge.

Formation of CCl4

6C=2,4 17Cl = 2,8,7...

What are the factors which result on the effective hydrogen bonding? Give one example each of intermolecular and intramolecular hydrogen bonding.

Hydrogen bonding isa special type of dipole-dipole attraction between molecules. It results from the attractive force between a hydrogen atom(covalently bonded to a very E.N. atom such as a N, O, or F atom) and another very electronegative atom( N,O or F).
The factors for effective hydrogen bonding are:1. Electronegativity of the atom must be high.2. Atomic size of the E.N. atom must be small. So, only F,O and N are able to make H-bond.
Intermolecular hydrogen bonding:
-Water (HO)

-Alcohol (R-OH)...

What is resonance? Are the resonance structures be the actual structure of molecules? Draw resonance structure of ozone (O) and Sulphur trioxide (SO).

Resonance isa way of describing delocalized electrons within certain molecules or polyatomic ions where the bonding cannot be expressed by a single Lewis formula. A molecule or ion with such delocalized electrons is represented by several resonance structures.

When it is possible to write more than one equivalent resonance structure for a molecule or ion,the actual structure is the average of the resonance structures.Butresonance structures represent different ways of placing electrons on the...

Ammonia has higher boiling point than phosphine. Give reason.

It is due to inter-molecular hydrogen bond.

Nitrogen present in ammonia is capable of forming hydrogen bonding with neighboring ammonia molecules which increases their intermolecular force of attraction. As a result, higher amount of heat energy needs to be supplied to break this bond. So, it has a higher boiling point.

However, hydrogen bonding cannot be imagined in Phosphine.