What is intermolecular forces?

Intermolecular forces is define as the interaction between atoms or molecules in a substance that is called intermolecular forces. Generally, stronger intermolecular forces occur in polar molecules. strongest intermolecular forces such as hydrogen bonding. the strongest intermolecular forces occur only in polar molecules.

For example

NH3 (Ammonia)

You know that, there are three main different types of intermolecular forces exist in nh3 molecules. such as,

Hydrogen bonding, Dipole dipole interaction, London dispersion forces. these three intermolecular forces are present in ammonia molecules.

lets know in details,

first off all, we discuss about hydrogen bonding, hydrogen bond is known as strongest intermolecular forces. these bonds are present between ammonia.


Hydrogen bonding

Hydrogen bonding occur in ammonia molecules.

Reason is this that, if you look at the structure of ammonia molecules, hydrogen are directly attached with high electronegative atom such as, nitrogen (N). If any molecules bound to highly electronegative elements then they generate hydrogen bonds between two molecules such as, N-H, H-O, and H-F then it makes hydrogen bond between molecules. Due to large difference of electronegativity. and the negative charge is appear on nitrogen and positive charge is appear on hydrogen. due to this both atoms are attract each other. and due to this attraction hydrogen bonds are generated between molecules.

The difference in electronegativity between two atoms., such as, N and H. the value of electronegative of nitrogen is 3.0 and the value electronegative of hydrogen is 2.2. it mean nitrogen has highly electronegative atoms compare with hydrogen. the difference of electronegativity between atoms is (0.8). Therefore, the large difference in electronegativity between the N atom and H atom, N-O, N-F atoms leads to highly polar covalent bond. so, you can say that, polar molecules generated hydrogen bonding.

Hydrogen atom are directly attached with high electronegative atom. Such as, N, O, F. and element has one loan pair electron. This molecules is called highly polarized molecules. in this case, partial positive charge appear on hydrogen and partial negative chare appear on nitrogen. there are two highly polarized molecules. and both are attract each other. partial positive charge of hydrogen are attracted with partial negative charge of other molecules.

As a result attraction forces is produced between them. this type of forces is called hydrogen bonding. hydrogen bonding is also called intermolecular forces between two molecules. Hydrogen bonds also occur between hydrogen fluoride molecules. and atmos are bound to highly electronegative elements. and it has available loan pair electron. therefore, it is more possibility to make hydrogen bonding.

What are the strongest intermolecular forces?

The strongest intermolecular forces generally, occur in dipole dipole interaction and the dipole dipole interaction occur in polar molecules because polar molecules have two poles (one is positive and another is negative). that is the reason, the dipole dipole interaction is possible and it gives strongest intermolecular forces such as hydrogen bonding.

For examples

1 H2O (Water molecules)

Yes, it is true the strongest intermolecular forces (hydrogen bonding) occur in water molecules.

Lets know in details

Yes, there are three types of intermolecular forces occur in water molecules, such as hydrogen bonding, dipole – induced dipole forces and London dispersion forces.

The negative O atom are attract the positive H atoms in a adjacent molecules. As a result, dipole dipole interaction is done and hydrogen bonding are formed.

So, we can day that the strongest intermolecular forces is dipole dipole interaction.

You, know that, water molecules does have a dipole moments because oxygen is more electronegative then hydrogen.

Water molecules ate polar dipoles because the unequal sharing of electrons between the atoms and the unsymmetrical shape of the molecules. this mean,

Water molecules has two poles

A positive charge on the hydrogen pole (one side).

A negative charge on the oxygen pole (another side).

You know, there are two O-H bonds are in water molecules, because oxygen is more electronegative atom then hydrogen. the OH bonds is polar are formed. this is called covalent bonds.

A water molecules consist of two bonding pairs and two loan pairs.

2. CH3OH (Methanol molecules)

Yes, it is true strongest intermolecular forcess occur between two methanol molecules. such as, hydrogen bonding, dipole dipole forces, London dispersion forces.

Actually, hydrogen bonding is present between two methanol molecules because oxygen is directly attached to hydrogen and due to this hydrogen bonding form. this forces is called strong intermolecular forces and it occur between oxygen and hydrogen. You know that oxygen is highly electronegativity atoms compare with hydrogen.due to this, oxygen has partial negative charge whereas hydrogen has partial positive charge. According to this, both atoms are attracted each other. As a results hydrogen bonding occur between this two methanol molecule. and in case of ethanol molecules there same types of intermolecular occur between two ethanol molecules. The intermolecular forces of ethanol are, hydrogen bonding, dipole dipole forces. and i meant to say that the ethanol intermolecular forces are hydrogen bonding, dipole dipole interaction. this mean, the same intermolecular forces occur between, two methanol or ethanol molecules.

Dipole-dipole interaction occur in methanol because it creat dipole moment between molecules due to the presence of the electronegative oxygen atom.

The electronegative atom which is oxygen that create a permanent positive charge on the molecules and rest of the molecules are create partial negative charge that are easily create parmanent dipole within each of the methanol molecules with opposing charge. this type of interaction is called dipole-dipole interaction.

methanol are also generate london dispersion forces between two non polar molecules. the basic concepts is this that, the interaction between two non polar methanol molecules. it mean, one hydrogen atom of first methanol interacted with second hydrogen of second methanol molecules. But It generated very weak intermolecular forces. In other words, there is not any poles to interact each other. this is one type of interaction between two methanol molecules in which very weak intermolecular forces are generated. this weak interaction is know as London dispersion forces.

3. HCl

HCl are made “polar covalent bonds” when atoms share electrons between hydrogen and chloride. Polar covalent bonds atoms such as hydrogen and chloride. HCl is made covalent bonds not hydrogen bonds. Because covalent bonds made in the presence of sharing of electrons between hydrogen and chloride. hydrogen bonds are made if hydrogen are bound to strong electronegative elements such as, Nitrogen, oxygen, fluoride. but HCl intermolecular forces has dipole dipole interaction and London dispersion forces.

Cl is highly electronegative atoms compare with hydrogen. that why, partial negative charge are appear on Cl and partial positive charge appear on hydrogen. Due to this, both atoms interact each other and it generated dipole dipole forces and London dispersion forces. the hcl intermolecular forces are dipole dipole intraction, because it is a polar molecules. the dipole dipole interaction are more attracted on polar molecules. it is one type of strongest intermolecular forces of attraction. the intermolecular forces in hydrogen chloride are made as intermolecular hydrogen bonding. it is occur if H (hydrogen) is bound to strongly electronegative elements. nitrogen and oxygen is a one type of strongest electronegative elements. If it is bound to (N) nitrogen or (O) oxygen then it make hydrogen bonding otherwise it can’t be made hydrogen bonding.

dipole-dipole intraction, and LDF occur between HCl molecules. and Both intermolecular forces are exist between HCl. it occur specially in polar molecules.

What are the Strongest to Weakest Intermolecular forces?

Ion Dipole Forces – Ion dipole forces are the weakest intermolecular forces. But it is strongest compare with hydrogen bonding. Yes, it is absolutely true, ion dipole forces is much weakest compare with covalent bond and hydrogen bond.

When ion (Catonic Or iononic such as Cl) and dipole such as (hcl) interact each other. this interaction between ion and dipole is called ion dipole forces. due to this interaction weaker intermolecular forces are generated.

Lets know with examples

Take ion and Dipole

Ion – Cl

Dipole – HCl

When ion and dipole are interacted each other, then highly strongest intermolecular forces are generated between ion and dipole.

In case of ion dipole forces, Cl interacted with HCl it give strongest type of intermolecular forces, ion dipole forces is strongest intermolecular forces compare with hydrogen bonding. When Cl interacted with H because Cl has partial negative charge and hydrogen have partial positive charge then both Cl and Hydrogen are interact each other. Other reason is Cl is highly electronegativity atom compare with hydrogen.

Therefore, after interaction between Cl and H then it gives ion dipole forces. this forces is called strongest intermolecular forces.

Hydrogen bonding – Hydrogen bonds occur when hydrogen are attached with very electronegative atoms such as, nitrogen, oxygen. hydrogen bonding are created when if hydrogen make N-H bonds, N-O bonds or N-F bonds.

NH3 is best example of hydrogen bonding intermolecular forces.

NH3 – hydrogen bonding occur between nh3 molecules because if you look at the structure of nh3, hydrogen are directly attached with high electronegative atom such as nitrogen (N). we know that, if any molecules bound to highly electronegative elements such as, N, O, and F then it make hydrogen bonds between molecules due to large difference of electronegativity. it mean, nitrogen is highly electronegative atom compare with hydrogen.

If hydrogen attached with highly electronegative atoms such as, N, O, F. then this types of bonds is know as hydrogen bonding. these are the simple basic concepts for finding hydrogen bonding between molecules or atoms.

Dipole Dipole forces – Dipole-dipole intraction are attracted among polarized molecules. we know that polarized molecules has two poles partial positive pole and partial negative pole. therefore it is called dipole. dipole dipole intraction occur between two polarized molecules or between two polarized dipole.consider the one dipole, it has two pole partial positive pole and partial negative poles. consider another dipole it has also two poles, partial positive pole and partial negative poles, we has two dipoles. So, the negative pole of one molecules attracted the positive pole of another molecules. due to this attractive forces are produces. this attractive forces is called dipole dipole intraction.

Van der waals forces – Van dar waals forces is weakest type of intermolecular forces. You know that this type of intermolecular forces is much weaker then covalent bond, ionic bond even hydrogen bond. van der waals forces have bond energy 8 kj/moles. it is used to find the intermolecular forces. It is also called secondary forces.

Van der waals forces occur in between class of molecules. Such as,

Van der waals forces occur between 2 polar molecules and also between 2 non polar molecules.

Vander waals forces also occur between ion and polar and ion and non polar.

Van der waals forces molecule – molecule can be attracted. and ion – molecule can be attracted.

Strongest to weakest order of intermolecular forces

Dipole Dipole interaction > Dipole induced dipole forces > London dispersion forces.

Dipole – Dipole interaction

Dipole dipole interaction exist between two polar molecules. and it work between the two permanent dipoles which interact between the partial positive charge ion of a molecules and the partially negative charge ion of another molecules.


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