Forces of AttractionForces of Attraction

IntroductionIntroduction

Atoms aggregate to form molecules and Atoms aggregate to form molecules and latticelattice

Molecules aggregate to form condensed Molecules aggregate to form condensed phases of mattephases of matte

Aggregation of atoms, appositively Aggregation of atoms, appositively charged ions and molecules is a charged ions and molecules is a

consequence ofconsequence of

Electrical forces exerted on the electrons Electrical forces exerted on the electrons of one particle by the nucleus (or nuclei) of of one particle by the nucleus (or nuclei) of the otherthe other

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Two broad categories of forces of Two broad categories of forces of attractionattraction

Intramolecular- forces that exist within Intramolecular- forces that exist within molecules or fundamental/formula unitsmolecules or fundamental/formula units

(forces that hold atoms or ions in a (forces that hold atoms or ions in a compound)compound)

Intermolecular- forces of attraction that Intermolecular- forces of attraction that exist between the molecules in a exist between the molecules in a compoundcompound

Intramolecular ForcesIntramolecular Forces

Three typesThree types

1.1. Ionic Ionic

2.2. CovalentCovalent

3.3. metallicmetallic

Ionic or Electrovalent BondIonic or Electrovalent Bond

Electrostatic force of attraction between Electrostatic force of attraction between ions of opposite chargeions of opposite charge

Ions are formed from atoms as a result of Ions are formed from atoms as a result of electron transfer from one atom to anotherelectron transfer from one atom to another

Formed as a result of a large difference in Formed as a result of a large difference in electronegativity of atomselectronegativity of atoms

Formed between metals and non-metalsFormed between metals and non-metals

Electronegativity- the ability of an atom Electronegativity- the ability of an atom to attract (pull) electrons to itself.to attract (pull) electrons to itself.

Electrostatic force depends on the charge Electrostatic force depends on the charge on the ions.on the ions.

PropertiesProperties

Crystalline solids- rigidity and strengthCrystalline solids- rigidity and strength

High melting and boiling pointsHigh melting and boiling points

Conduct electricity in molten and aqueous Conduct electricity in molten and aqueous statestate

They are hardThey are hard

They are brittleThey are brittle

Soluble in polar solvents such as water Soluble in polar solvents such as water (solute-solvent interactions)(solute-solvent interactions)

Covalent BondsCovalent Bonds

Formed between atoms with a small difference Formed between atoms with a small difference in electronegativityin electronegativity

Formed by the overlapping of atomic orbital.Formed by the overlapping of atomic orbital.

Molecular orbital resultMolecular orbital result

Electrons are shared between nuclei of the two Electrons are shared between nuclei of the two atomsatoms

The attraction between the shared electrons and The attraction between the shared electrons and the nuclei that holds the molecule togetherthe nuclei that holds the molecule together

Two types of bonds are formed Two types of bonds are formed

1.1. Either sigma bondsEither sigma bonds

2.2. Or pi bondsOr pi bonds

Sigma bondsSigma bonds

Three possible ways for a sigma bond to Three possible ways for a sigma bond to be formedbe formed

1.1. Overlapping of two S-orbitalOverlapping of two S-orbital

2.2. Overlapping of an S and a P-orbitalOverlapping of an S and a P-orbital

3.3. Head to head overlapping of two P-Head to head overlapping of two P-orbitalorbital

Pi bondsPi bonds

The side to side overlapping of two P The side to side overlapping of two P orbital.orbital.

Electrons in this bond are delocalizedElectrons in this bond are delocalized

The electron density is above and below The electron density is above and below the plane of the sigma bond.the plane of the sigma bond.

These bonds make a compound reactive These bonds make a compound reactive

example in alkenes with the c-c double example in alkenes with the c-c double bond.bond.

Properties of Covalent CompoundsProperties of Covalent Compounds

Liquids and gases at room temperatureLiquids and gases at room temperature

Relatively low boiling point.Relatively low boiling point.

Do not conduct electricityDo not conduct electricity

Insoluble in polar solventInsoluble in polar solvent

Soluble in non-polar solventSoluble in non-polar solvent

Dative (Coordinate) covalent BondDative (Coordinate) covalent Bond

One atom donates both electrons to form One atom donates both electrons to form a covalent bonda covalent bond

Recall- in a normal covalent bond each Recall- in a normal covalent bond each atom donates an electron to be shared.atom donates an electron to be shared.

The atom donating the electrons must The atom donating the electrons must have at least one lone pair of the have at least one lone pair of the electrons.electrons.

The other atom must have an available The other atom must have an available empty orbital to accommodate this empty orbital to accommodate this electron pairelectron pair

example, boron trifluoride, aluminium example, boron trifluoride, aluminium trichloride.trichloride.

can bond with say ammonia.can bond with say ammonia.

Metallic BondsMetallic Bonds

Positive ions surrounded by a sea of Positive ions surrounded by a sea of mobile (delocalized) electrons.mobile (delocalized) electrons.

Strong electrostatic force of attraction Strong electrostatic force of attraction binds the system togetherbinds the system together

Attraction between valence electrons and Attraction between valence electrons and metal ionmetal ion

What influences the strength of the What influences the strength of the bond?bond?

Availability of electronsAvailability of electrons

-- More available delocalized electrons, the More available delocalized electrons, the stronger the electrostatic attraction, the stronger the electrostatic attraction, the stronger the metallic bond.stronger the metallic bond.

Size of the charge on metal ionSize of the charge on metal ion

- Larger charge size, stronger the metallic Larger charge size, stronger the metallic bond. Explain.bond. Explain.

example Al and Naexample Al and Na

hard metal and soft metalhard metal and soft metal

Properties of metalsProperties of metals

Hardness- Hardness refers to the ability of Hardness- Hardness refers to the ability of a metal to resist abrasion, penetration, a metal to resist abrasion, penetration, cutting action, or permanent distortion cutting action, or permanent distortion

Brittleness- Brittleness is the property of a Brittleness- Brittleness is the property of a metal that allows little bending or metal that allows little bending or deformation without shattering deformation without shattering

Malleability- A metal that can be Malleability- A metal that can be hammered, rolled, or pressed into various hammered, rolled, or pressed into various shapes without cracking or breaking or shapes without cracking or breaking or other detrimental effects is said to be other detrimental effects is said to be malleable. malleable.

Ductility- Ductility is the property of a metal Ductility- Ductility is the property of a metal that permits it to be permanently drawn, that permits it to be permanently drawn, bent, or twisted into various shapes bent, or twisted into various shapes without breaking without breaking

Elasticity- Elasticity is that property that Elasticity- Elasticity is that property that enables a metal to return to its original enables a metal to return to its original shape when the force that causes the shape when the force that causes the change of shape is removed. change of shape is removed.

ToughnessToughness

DensityDensity

Fusibility Fusibility

Conductivity- Conductivity is the property Conductivity- Conductivity is the property that enables a metal to carry heat or that enables a metal to carry heat or electricity electricity

Contraction Contraction

ExpansionExpansion

Polar Covalent Bonds and Dipole Polar Covalent Bonds and Dipole MomentsMoments

Polar bonds- formed between atoms of Polar bonds- formed between atoms of different electronegativity (EN)different electronegativity (EN)- example, chlorine-carbon bond- example, chlorine-carbon bond * chlorine is more EN than carbon* chlorine is more EN than carbon * chlorine attracts the shared electron pair * chlorine attracts the shared electron pair

to itself.to itself. * C-Cl bond is polarized (delta negative * C-Cl bond is polarized (delta negative and delta positiveand delta positive

Polarized bonds have dipole moment.Polarized bonds have dipole moment.

Dipole- Dipole- separation of charge within separation of charge within moleculesmolecules

Intermolecular ForcesIntermolecular Forces

What are the forces between one What are the forces between one chlorine molecule and another?chlorine molecule and another?

Intermolecular forces-Intermolecular forces- forces between forces between molecules or ions and influence their molecules or ions and influence their properties.properties.

Molecular polarityMolecular polarity gives rise to the forces gives rise to the forces of attraction between moleculesof attraction between molecules

characteristicscharacteristics

These forces are electrical – result from These forces are electrical – result from mutual attraction or mutual repulsion.mutual attraction or mutual repulsion.

Generally very weak forces of attractionGenerally very weak forces of attraction

Responsible for the states of matterResponsible for the states of matter

Characteristic FeaturesCharacteristic Features

Attractions exerted by one molecule of a Attractions exerted by one molecule of a molecular substance on another, such as molecular substance on another, such as the force of attraction between water the force of attraction between water molecules in ice. molecules in ice.

Attractions between molecules of one Attractions between molecules of one substance and molecules of another, as substance and molecules of another, as when two liquids are mixed, or a molecular when two liquids are mixed, or a molecular solid such as sugar is dissolved in a liquid. solid such as sugar is dissolved in a liquid.

Attractions between atoms of the noble Attractions between atoms of the noble gas elements, helium through radon.gas elements, helium through radon.

Attraction between molecules of one Attraction between molecules of one substance and ions of another, as when substance and ions of another, as when an ionic compound dissolves in a liquid. an ionic compound dissolves in a liquid.

Types of I.M.FTypes of I.M.F

Ion-dipoleIon-dipole

Dipole-dipoleDipole-dipole

London dispersion forcesLondon dispersion forces

Hydrogen bondsHydrogen bonds

Ion-Dipole ForcesIon-Dipole Forces

Result from electrical interactions between Result from electrical interactions between an ion and the partial charges on a polar an ion and the partial charges on a polar molecule.molecule.

Dipolar molecule- a substance with both a Dipolar molecule- a substance with both a positive and negative endspositive and negative ends

In the presence of ions dipolar molecules In the presence of ions dipolar molecules orient themselves with positive end of orient themselves with positive end of dipole near the anion and negative end dipole near the anion and negative end near cationnear cation

Magnitude of interaction depends on Magnitude of interaction depends on charge.charge.

example: NaCl in water (ionic substance in example: NaCl in water (ionic substance in dipolar water molecules).dipolar water molecules).

Dipole-Dipole forces-Dipole-Dipole forces- Intermolecular Intermolecular forces that operate between neutral forces that operate between neutral molecules having molecular dipole molecules having molecular dipole moments are called dipole-dipole forces moments are called dipole-dipole forces

Result from interactions among dipoles on Result from interactions among dipoles on neighbouring molecules.neighbouring molecules.

The more polar the substance the , the The more polar the substance the , the greater the strength of its dipole-dipole greater the strength of its dipole-dipole interactions.interactions.

The stronger the I.M.F that must be The stronger the I.M.F that must be overcome for a substance to boil or melt.overcome for a substance to boil or melt.

Permanent DipolePermanent Dipole

Inductive Forces and DispersionInductive Forces and Dispersion

InductiveInductive forces arise from the forces arise from the distortiondistortion of the charge cloud induced by the of the charge cloud induced by the presence of another molecule nearby. presence of another molecule nearby.

Distortion arises from the electric field Distortion arises from the electric field produced by the charge distribution of the produced by the charge distribution of the nearby molecule. nearby molecule.

These forces are These forces are always attractivealways attractive but but shorter ranged than electrostatic forces. shorter ranged than electrostatic forces.

If a charged molecule (ion) induces a If a charged molecule (ion) induces a dipole moment in a nearby neutral dipole moment in a nearby neutral molecule, the two molecules will stick molecule, the two molecules will stick together, even though the neutral together, even though the neutral molecule was initially round and molecule was initially round and unchargeduncharged

Dipole-Induced DipoleDipole-Induced Dipole

What would happen if HCl is mixed with What would happen if HCl is mixed with argon, which has no dipole moment?argon, which has no dipole moment?

- The electrons on an argon atom are - The electrons on an argon atom are distributed homogeneously around the distributed homogeneously around the nucleus of the atom.nucleus of the atom.

- Electrons are in constant motion. - Electrons are in constant motion.

Argon close to a polar HCl molecule, the Argon close to a polar HCl molecule, the electrons can shift to one side of the electrons can shift to one side of the nucleus to produce a very small dipole nucleus to produce a very small dipole moment that lasts for only an instant. moment that lasts for only an instant.

Distorting the distribution of electrons Distorting the distribution of electrons around the argon atom, the polar HCl around the argon atom, the polar HCl molecule induces a small dipole moment molecule induces a small dipole moment on this atom.on this atom.

A weak dipole-induced dipole force of A weak dipole-induced dipole force of attraction between the HCl molecule and attraction between the HCl molecule and the Ar atom is createdthe Ar atom is created

Dipole-Induced DipoleDipole-Induced Dipole

Induced Dipole- Induced DipoleInduced Dipole- Induced Dipole

Some atoms are perfectly symmetrical. Some atoms are perfectly symmetrical.

No dipole existNo dipole exist

Some forces must existSome forces must exist

Atoms and Molecules such as; the noble Atoms and Molecules such as; the noble gases, the halogens etc.gases, the halogens etc.

Electrons are in constant motion.Electrons are in constant motion.

Example: Helium atomExample: Helium atom

Movement of the electrons around the Movement of the electrons around the nuclei of a pair of neighboring helium nuclei of a pair of neighboring helium atoms can become synchronized so that atoms can become synchronized so that each atom simultaneously obtains an each atom simultaneously obtains an induced dipole moment. induced dipole moment.

There are fluctuations in electron density There are fluctuations in electron density occurring constantly.occurring constantly.

Creating an induced dipole-induced dipole Creating an induced dipole-induced dipole force of attraction between pairs of atoms. force of attraction between pairs of atoms.

This force is relatively weak in helium.This force is relatively weak in helium.

Atoms or molecules become more Atoms or molecules become more polarizable as they become larger polarizable as they become larger because there are more electrons to be because there are more electrons to be polarized. polarized.

Induced Dipole- Induced DipoleInduced Dipole- Induced Dipole

Hydrogen BondingHydrogen Bonding

Hydrogen Bonding-Hydrogen Bonding- a special kind of a special kind of dipole-dipole force that occurs when a dipole-dipole force that occurs when a hydrogen atom is bonded to one of the hydrogen atom is bonded to one of the very electronegative atoms, F, O, or N. very electronegative atoms, F, O, or N.

Electronegative atom must have at least a Electronegative atom must have at least a lone pair of electronslone pair of electrons

Hydrogen BondingHydrogen Bonding

Combination of forcesCombination of forces

- normal covalent bond- normal covalent bond

- dipole-dipole interaction- dipole-dipole interaction

Hydrogen BondingHydrogen Bonding

The H-F, H-O, and H-N bonds are very The H-F, H-O, and H-N bonds are very polar, because the electronegative atom polar, because the electronegative atom draws the bonding electron pair strongly to draws the bonding electron pair strongly to itself. This leaves the hydrogen nucleus itself. This leaves the hydrogen nucleus exposed exposed

Hydrogen Bonding in waterHydrogen Bonding in water

Summary I.M.FSummary I.M.F

Summary of Forces of AttractionSummary of Forces of Attraction

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